Calculate the number of business days between two dates

Question

In C   how can I calculate the number of business  or weekdays  days between two dates

User · Answer

I just improved  Alexander and  Slauma answer to support a business week as a parameter  for cases where saturday is a business day  or even cases where there is just a couple of days of the week that are considered business days        lt summary gt      Calculate the number of business days between two dates  considering       - Days of the week that are not considered business days       - Holidays between these two dates       lt  summary gt       lt param name  fDay  gt First day of the desired  span   lt  param gt       lt param name  lDay  gt Last day of the desired  span   lt  param gt       lt param name  BusinessDaysOfWeek  gt Days of the week that are considered to be business days  if NULL considers monday  tuesday  wednesday  thursday and friday as business days of the week  lt  param gt       lt param name  Holidays  gt Holidays  if NULL  considers no holiday  lt  param gt       lt returns gt Number of business days during the  span  lt  returns gt  public static int BusinessDaysUntil this DateTime fDay  DateTime lDay  DayOfWeek   BusinessDaysOfWeek   null  DateTime   Holidays   null        if  BusinessDaysOfWeek    null          BusinessDaysOfWeek   new DayOfWeek     DayOfWeek Monday  DayOfWeek Tuesday  DayOfWeek Wednesday  DayOfWeek Thursday  DayOfWeek Friday        if  Holidays    null          Holidays   new DateTime             fDay   fDay Date      lDay   lDay Date       if  fDay  gt  lDay          throw new ArgumentException  Incorrect last day     lDay        int bDays    lDay - fDay  Days   1      int fullWeekCount   bDays   7      int fullWeekCountMult   7 - WeekDays Length          Find out if there are weekends during the time exceedng the full weeks     if  bDays  gt   fullWeekCount   7                 int fDayOfWeek    int fDay DayOfWeek          int lDayOfWeek    int lDay DayOfWeek           if  fDayOfWeek  gt  lDayOfWeek              lDayOfWeek    7              If they are the same  we already covered it right before the Holiday subtraction         if  lDayOfWeek    fDayOfWeek                            Here we need to see if any of the days between are considered business days             for  int i   fDayOfWeek  i  lt   lDayOfWeek  i                    if   WeekDays Contains  DayOfWeek  i  gt  6   i - 7   i                        bDays -  1                           Subtract the days that are not in WeekDays   during the full weeks in the interval     bDays -   fullWeekCount   fullWeekCountMult           Subtract the number of bank holidays during the time interval     bDays   bDays - Holidays Select x   gt  x Date  Count x   gt  fDay  lt   x  amp  amp  x  lt   lDay        return bDays

User · Answer

Define an Extension Method on DateTime like so   public static class DateTimeExtensions       public static bool IsWorkingDay this DateTime date                return date DayOfWeek    DayOfWeek Saturday              amp  amp  date DayOfWeek    DayOfWeek Sunday            Then  use is within a Where clause to filter a broader list of dates   var allDates   GetDates       method which returns a list of dates     filter dates by working day s   var countOfWorkDays   allDates       Where day   gt  day IsWorkingDay          Count

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public enum NonWorkingDays   SaturdaySunday   0  FridaySaturday   1            public int getBusinessDates DateTime dateSt  DateTime dateNd  NonWorkingDays nonWorkingDays   NonWorkingDays SaturdaySunday                        List lt DateTime gt  datelist   new List lt DateTime gt                 while  dateSt Date  lt  dateNd Date                                datelist Add  dateSt   dateSt AddDays 1                               if  nonWorkingDays    NonWorkingDays SaturdaySunday                                return datelist Count d   gt  d DayOfWeek    DayOfWeek Saturday  amp  amp                         d DayOfWeek    DayOfWeek Friday                             else                               return datelist Count d   gt  d DayOfWeek    DayOfWeek Friday  amp  amp                         d DayOfWeek    DayOfWeek Saturday

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Ok  I think it s time to post the right answer  public static double GetBusinessDays DateTime startD  DateTime endD        double calcBusinessDays           1     endD - startD  TotalDays   5 -          startD DayOfWeek - endD DayOfWeek    2    7       if  endD DayOfWeek    DayOfWeek Saturday  calcBusinessDays--      if  startD DayOfWeek    DayOfWeek Sunday  calcBusinessDays--       return calcBusinessDays     Original Source  http   alecpojidaev wordpress com 2009 10 29 work-days-calculation-with-c

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I think none of the above answers are actually correct  None of them solves all the special cases such as when the dates starts and ends on the middle of a weekend  when the date starts on a Friday and ends on next Monday  etc  On top of that  they all round the calculations to whole days  so if the start date is in the middle of a saturday for example  it will substract a whole day from the working days  giving wrong results     Anyway  here is my solution that is quite efficient and simple and works for all cases  The trick is just to find the previous Monday for start and end dates  and then do a small compensation when start and end happens during the weekend   public double WorkDays DateTime startDate  DateTime endDate           double weekendDays           double days   endDate Subtract startDate  TotalDays           if days lt 0  return 0           DateTime startMonday   startDate AddDays DayOfWeek Monday - startDate DayOfWeek  Date          DateTime endMonday   endDate AddDays DayOfWeek Monday - endDate DayOfWeek  Date           weekendDays     endMonday Subtract startMonday  TotalDays    7    2              compute fractionary part of weekend days         double diffStart   startDate Subtract startMonday  TotalDays - 5          double diffEnd   endDate Subtract endMonday  TotalDays - 5              compensate weekenddays         if diffStart gt 0  weekendDays -  diffStart          if diffEnd gt 0  weekendDays    diffEnd           return days - weekendDays

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Well this has been beaten to death     However I m still going to provide another answer because I needed something a bit different  This solution is different in that it returns a Business TimeSpan between the start and end  and you can set the business hours of the day  and add holidays  So you can use it to calculate if it happens within a day  across days  over weekends  and even holidays  And you can get just the business days or not by just getting what you need from the returned TimeSpan object  And the way it uses lists of days  you can see how very easy it would be to add the list of non-work days if it s not the typical Sat and Sun  And I tested for a year  and it seems super fast   I just hope the pasting of the code is accurate  But I know it works   public static TimeSpan GetBusinessTimespanBetween      DateTime start  DateTime end      TimeSpan workdayStartTime  TimeSpan workdayEndTime      List lt DateTime gt  holidays   null        if  end  lt  start          throw new ArgumentException  start datetime must be before end datetime             Just create an empty list for easier coding      if  holidays    null  holidays   new List lt DateTime gt          if  holidays Where x   gt  x TimeOfDay Ticks  gt  0  Any            throw new ArgumentException  holidays can not have a TimeOfDay  only the Date          var nonWorkDays   new List lt DayOfWeek gt      DayOfWeek Saturday  DayOfWeek Sunday         var startTime   start TimeOfDay          If the start time is before the starting hours  set it to the starting hour      if  startTime  lt  workdayStartTime  startTime   workdayStartTime       var timeBeforeEndOfWorkDay   workdayEndTime - startTime          If it s after the end of the day  then this time lapse doesn t count      if  timeBeforeEndOfWorkDay TotalSeconds  lt  0  timeBeforeEndOfWorkDay   new TimeSpan           If start is during a non work day  it doesn t count      if  nonWorkDays Contains start DayOfWeek   timeBeforeEndOfWorkDay   new TimeSpan        else if  holidays Contains start Date   timeBeforeEndOfWorkDay   new TimeSpan         var endTime   end TimeOfDay          If the end time is after the ending hours  set it to the ending hour      if  endTime  gt  workdayEndTime  endTime   workdayEndTime       var timeAfterStartOfWorkDay   endTime - workdayStartTime          If it s before the start of the day  then this time lapse doesn t count      if  timeAfterStartOfWorkDay TotalSeconds  lt  0  timeAfterStartOfWorkDay   new TimeSpan           If end is during a non work day  it doesn t count      if  nonWorkDays Contains end DayOfWeek   timeAfterStartOfWorkDay   new TimeSpan        else if  holidays Contains end Date   timeAfterStartOfWorkDay   new TimeSpan            Easy scenario if the times are during the day day      if  start Date CompareTo end Date     0                if  nonWorkDays Contains start DayOfWeek   return new TimeSpan            else if  holidays Contains start Date   return new TimeSpan            return endTime - startTime            else               var timeBetween   end - start          var daysBetween    int Math Floor timeBetween TotalDays           var dailyWorkSeconds    int Math Floor  workdayEndTime - workdayStartTime  TotalSeconds            var businessDaysBetween   0              Now the fun begins with calculating the actual Business days          if  daysBetween  gt  0                        var nextStartDay   start AddDays 1  Date              var dayBeforeEnd   end AddDays -1  Date              for  DateTime d   nextStartDay  d  lt   dayBeforeEnd  d   d AddDays 1                                 if  nonWorkDays Contains d DayOfWeek   continue                  else if  holidays Contains d Date   continue                  businessDaysBetween                                     var dailyWorkSecondsToAdd   dailyWorkSeconds   businessDaysBetween           var output   timeBeforeEndOfWorkDay   timeAfterStartOfWorkDay          output   output   new TimeSpan 0  0  dailyWorkSecondsToAdd            return output            And here is test code  Note that you just have to put this function in a class called DateHelper for the test code to work    TestMethod  public void TestGetBusinessTimespanBetween         var workdayStart   new TimeSpan 8  0  0       var workdayEnd   new TimeSpan 17  0  0        var holidays   new List lt DateTime gt                  new DateTime 2018  1  15      a Monday         new DateTime 2018  2  15     a Thursday             var testdata   new                 new                       expectedMinutes   0              start   new DateTime 2016  10  19  9  50  0               end   new DateTime 2016  10  19  9  50  0                     new                       expectedMinutes   10              start   new DateTime 2016  10  19  9  50  0               end   new DateTime 2016  10  19  10  0  0                     new                       expectedMinutes   5              start   new DateTime 2016  10  19  7  50  0               end   new DateTime 2016  10  19  8  5  0                     new                       expectedMinutes   5              start   new DateTime 2016  10  19  16  55  0               end   new DateTime 2016  10  19  17  5  0                     new                       expectedMinutes   15              start   new DateTime 2016  10  19  16  50  0               end   new DateTime 2016  10  20  8  5  0                     new                       expectedMinutes   10              start   new DateTime 2016  10  19  16  50  0               end   new DateTime 2016  10  20  7  55  0                     new                       expectedMinutes   5              start   new DateTime 2016  10  19  17  10  0               end   new DateTime 2016  10  20  8  5  0                     new                       expectedMinutes   0              start   new DateTime 2016  10  19  17  10  0               end   new DateTime 2016  10  20  7  5  0                     new                       expectedMinutes   545              start   new DateTime 2016  10  19  12  10  0               end   new DateTime 2016  10  20  12  15  0                        Spanning multiple weekdays         new                       expectedMinutes   835              start   new DateTime 2016  10  19  12  10  0               end   new DateTime 2016  10  21  8  5  0                        Spanning multiple weekdays         new                       expectedMinutes   1375              start   new DateTime 2016  10  18  12  10  0               end   new DateTime 2016  10  21  8  5  0                        Spanning from a Thursday to a Tuesday  5 mins short of complete day          new                       expectedMinutes   1615              start   new DateTime 2016  10  20  12  10  0               end   new DateTime 2016  10  25  12  5  0                        Spanning from a Thursday to a Tuesday  5 mins beyond complete day          new                       expectedMinutes   1625              start   new DateTime 2016  10  20  12  10  0               end   new DateTime 2016  10  25  12  15  0                        Spanning from a Friday to a Monday  5 mins beyond complete day          new                       expectedMinutes   545              start   new DateTime 2016  10  21  12  10  0               end   new DateTime 2016  10  24  12  15  0                        Spanning from a Friday to a Monday  5 mins short complete day          new                       expectedMinutes   535              start   new DateTime 2016  10  21  12  10  0               end   new DateTime 2016  10  24  12  5  0                        Spanning from a Saturday to a Monday  5 mins short complete day          new                       expectedMinutes   245              start   new DateTime 2016  10  22  12  10  0               end   new DateTime 2016  10  24  12  5  0                        Spanning from a Saturday to a Sunday  5 mins beyond complete day          new                       expectedMinutes   0              start   new DateTime 2016  10  22  12  10  0               end   new DateTime 2016  10  23  12  15  0                        Times within the same Saturday          new                       expectedMinutes   0              start   new DateTime 2016  10  22  12  10  0               end   new DateTime 2016  10  23  12  15  0                        Spanning from a Saturday to the Sunday next week          new                       expectedMinutes   2700              start   new DateTime 2016  10  22  12  10  0               end   new DateTime 2016  10  30  12  15  0                        Spanning a year          new                       expectedMinutes   143355              start   new DateTime 2016  10  22  12  10  0               end   new DateTime 2017  10  30  12  15  0                        Spanning a year with 2 holidays          new                       expectedMinutes   142815              start   new DateTime 2017  10  22  12  10  0               end   new DateTime 2018  10  30  12  15  0                         foreach  var item in testdata                Assert AreEqual item expectedMinutes              DateHelper GetBusinessTimespanBetween                  item start  item end                  workdayStart  workdayEnd                  holidays                   TotalMinutes

User · Answer

You just have to iterate through each day in the time range and subtract a day from the counter if its a Saturday or a Sunday       private float SubtractWeekend DateTime start  DateTime end            float totaldays    end Date - start Date  Days          var iterationVal   totalDays          for  int i   0  i  lt   iterationVal  i                  int dayVal    int start Date AddDays i  DayOfWeek              if dayVal    6    dayVal    0                       saturday or sunday                 totalDays--                                  return totalDays

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This solution avoids iteration  works for both  ve and -ve weekday differences and includes a unit test suite to regression against the slower method of counting weekdays  I ve also include a concise method to add weekdays also works in the same non-iterative way    Unit tests cover a few thousand date combinations in order to exhaustively test all start end weekday combinations with both small and large date ranges   Important  We make the assumption that we are counting days by excluding the start date and including the end date  This is important when counting weekdays as the specific start end days that you include exclude affect the result  This also ensures that the difference between two equal days is always zero and that we only include full working days as typically you want the answer to be correct for any time on the current start date  often today  and include the full end date  e g  a due date      NOTE  This code needs an additional adjustment for holidays but in keeping with the above assumption  this code must exclude holidays on the start date   Add weekdays   private static readonly int     addOffset           0  1  2  3  4      0  1  2  3  4      Su  0      0  1  2  3  4      M   1      0  1  2  3  6      Tu  2      0  1  4  5  6      W   3      0  1  4  5  6      Th  4      0  3  4  5  6      F   5      0  2  3  4  5      Sa  6     public static DateTime AddWeekdays this DateTime date  int weekdays        int extraDays   weekdays   5      int addDays   weekdays  gt   0            weekdays   5    7    addOffset  int date DayOfWeek  extraDays             weekdays   5    7 -  addOffset 6 -  int date DayOfWeek  -extraDays       return date AddDays addDays       Compute weekday difference   static readonly int     diffOffset           Su M  Tu W  Th F  Sa      0  1  2  3  4  5  5      Su      4  0  1  2  3  4  4      M       3  4  0  1  2  3  3      Tu      2  3  4  0  1  2  2      W       1  2  3  4  0  1  1      Th      0  1  2  3  4  0  0      F       0  1  2  3  4  5  0      Sa     public static int GetWeekdaysDiff this DateTime dtStart  DateTime dtEnd        int daysDiff    int  dtEnd - dtStart  TotalDays      return daysDiff  gt   0           5    daysDiff   7     diffOffset  int  dtStart DayOfWeek   int  dtEnd DayOfWeek            5    daysDiff   7  -  diffOffset 6 -  int  dtStart DayOfWeek  6 -  int  dtEnd DayOfWeek       I found that most other solutions on stack overflow were either slow  iterative  or overly complex and many were just plain incorrect   Moral of the story is     Don t trust it unless you ve exhaustively tested it    Unit tests based on NUnit Combinatorial testing and ShouldBe NUnit extension    TestFixture  public class DateTimeExtensionsTests            lt summary gt          Exclude start date  Include end date          lt  summary gt           lt param name  dtStart  gt  lt  param gt           lt param name  dtEnd  gt  lt  param gt           lt returns gt  lt  returns gt      private IEnumerable lt DateTime gt  GetDateRange DateTime dtStart  DateTime dtEnd                Console WriteLine   dtStart  0 yy-MMM-dd ddd   dtEnd  1 yy-MMM-dd ddd    dtStart  dtEnd            TimeSpan diff   dtEnd - dtStart          Console WriteLine diff            if  dtStart  lt   dtEnd                        for  DateTime dt   dtStart AddDays 1   dt  lt   dtEnd  dt   dt AddDays 1                                 Console WriteLine   dt  0 yy-MMM-dd ddd    dt                   yield return dt                                  else                       for  DateTime dt   dtStart AddDays -1   dt  gt   dtEnd  dt   dt AddDays -1                                 Console WriteLine   dt  0 yy-MMM-dd ddd    dt                   yield return dt                                      Test  Combinatorial      public void TestGetWeekdaysDiff           Values 1  2  3  4  5  6  7  8  9  10  11  12  13  14  20  30           int startDay           Values 1  2  3  4  5  6  7  8  9  10  11  12  13  14  20  30           int endDay           Values 7           int startMonth           Values 7           int endMonth                   Arrange         DateTime dtStart   new DateTime 2016  startMonth  startDay           DateTime dtEnd   new DateTime 2016  endMonth  endDay            int nDays   GetDateRange dtStart  dtEnd               Count dt   gt  dt DayOfWeek    DayOfWeek Saturday  amp  amp  dt DayOfWeek    DayOfWeek Sunday            if  dtEnd  lt  dtStart  nDays   -nDays           Console WriteLine   countBusDays  0    nDays               Act   Assert         dtStart GetWeekdaysDiff dtEnd  ShouldBe nDays               Test  Combinatorial      public void TestAddWeekdays           Values 1  2  3  4  5  6  7  8  9  10  11  12  13  14  20  30           int startDay           Values 0  1  2  3  4  5  6  7  8  9  10  11  12  13  14  20  30           int weekdays                DateTime dtStart   new DateTime 2016  7  startDay           DateTime dtEnd1   dtStart AddWeekdays weekdays          ADD         dtStart GetWeekdaysDiff dtEnd1  ShouldBe weekdays              DateTime dtEnd2   dtStart AddWeekdays -weekdays         SUBTRACT         dtStart GetWeekdaysDiff dtEnd2  ShouldBe -weekdays

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Yet another approach for calculating business days  not considering holidays  but taking into account the time of day returning a fractional amount of days   public static double GetBusinessDays DateTime startD  DateTime endD        while  IsWeekend startD           startD   startD Date AddDays 1        while  IsWeekend endD           endD   endD Date AddDays -1        var bussDays    endD - startD  TotalDays -          2     int  endD - startD  TotalDays   7   -          startD DayOfWeek  gt  endD DayOfWeek   2   0        return bussDays     public static bool IsWeekend DateTime d        return d DayOfWeek    DayOfWeek Saturday    d DayOfWeek    DayOfWeek Sunday      You can fiddle with it here  https   rextester com ASHRS53997

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Here is an approach if you are using MVC  I have also calculated national holidays or any festive days to be excluded by fetching it from holidayscalendar which you will need to make one           foreach  DateTime day in EachDay model                         bool key   false              foreach  LeaveModel ln in holidaycalendar                                if  day Date    ln Date  amp  amp  day DayOfWeek    DayOfWeek Saturday  amp  amp  day DayOfWeek    DayOfWeek Sunday                                        key   true  break                                              if  day DayOfWeek    DayOfWeek Saturday    day DayOfWeek    DayOfWeek Sunday                                key   true                            if  key    true                                leavecount                              Leavemodel is a list here

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I know this question is already solved  but I thought I could provide a more straightforward-looking answer that may help other visitors in the future   Here s my take at it   public int GetWorkingDays DateTime from  DateTime to        var dayDifference    int to Subtract from  TotalDays      return Enumerable          Range 1  dayDifference           Select x   gt  from AddDays x            Count x   gt  x DayOfWeek    DayOfWeek Saturday  amp  amp  x DayOfWeek    DayOfWeek Sunday       This was my original submission   public int GetWorkingDays DateTime from  DateTime to        var totalDays   0      for  var date   from  date  lt  to  date   date AddDays 1                 if  date DayOfWeek    DayOfWeek Saturday              amp  amp  date DayOfWeek    DayOfWeek Sunday              totalDays               return totalDays

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int BusinessDayDifference DateTime Date1  DateTime Date2                int Sign   1          if  Date2  gt  Date1                        Sign   -1              DateTime TempDate   Date1              Date1   Date2              Date2   TempDate                    int BusDayDiff    int  Date1 Date - Date2 Date  TotalDays          if  Date1 DayOfWeek    DayOfWeek Saturday              BusDayDiff -  1          if  Date2 DayOfWeek    DayOfWeek Sunday              BusDayDiff -  1          int Week1   GetWeekNum Date1           int Week2   GetWeekNum Date2           int WeekDiff   Week1 - Week2          BusDayDiff -  WeekDiff   2          foreach  DateTime Holiday in Holidays              if  Date1  gt   Holiday  amp  amp  Date2  lt   Holiday                  BusDayDiff--          BusDayDiff    Sign          return BusDayDiff             private int GetWeekNum DateTime Date                return  int  Date AddDays - int Date DayOfWeek  Ticks   TimeSpan TicksPerDay   7

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So I had a similar task except I had to calculate business days left  from date should not be more than to date   and end date should skip to next business day  To make it more understandable readable  I did this in the following steps  Updated toDate to the next business day if it is on weekend   Find out the number of complete weeks between dates  and for each complete week consider 5 days in running total   Now days left are only different of from and to weekdays  it won t be more than 6 days   so wrote a small loop to get it  skip Saturday and Sunday   public static int GetBusinessDaysLeft DateTime fromDate  DateTime toDate            Validate that startDate should be less than endDate      if  fromDate  gt   toDate  return 0          Move end date to Monday if on weekends      if  toDate DayOfWeek    DayOfWeek Saturday    toDate DayOfWeek    DayOfWeek Sunday           while  toDate DayOfWeek    DayOfWeek Monday               toDate   toDate AddDays  1           Consider 5 days per complete week in between start and end dates      int remainder  quotient   Math DivRem  toDate - fromDate  Days  7  out remainder        var daysDiff   quotient   5        var curDay   fromDate       while  curDay DayOfWeek    toDate DayOfWeek                  curDay   curDay AddDays 1            if  curDay DayOfWeek    DayOfWeek Saturday    curDay DayOfWeek    DayOfWeek Sunday               continue            daysDiff    1              return daysDiff

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Here is the function which we can use to calculate business days between two date  I m not using holiday list as it can vary accross country region    If we want to use it anyway we can take third argument as list of holiday and before incrementing count we should check that list does not contains d  public static int GetBussinessDaysBetweenTwoDates DateTime StartDate    DateTime EndDate                if  StartDate  gt  EndDate              return -1           int bd   0           for  DateTime d   StartDate  d  lt  EndDate  d   d AddDays 1                         if  d DayOfWeek    DayOfWeek Saturday  amp  amp  d DayOfWeek    DayOfWeek Sunday                  bd                       return bd

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Here s another example you can choose the weekend dates as well    public int GetBuisnessDays DateTime StartDate  DateTime EndDate                int counter   0           if  StartDate Date    EndDate Date                        if  StartDate DayOfWeek    DayOfWeek Saturday  amp  amp  StartDate DayOfWeek    DayOfWeek Friday                  return 1              return 0                     while  StartDate  lt   EndDate                        if  StartDate DayOfWeek    DayOfWeek Saturday  amp  amp  StartDate DayOfWeek    DayOfWeek Friday                    counter              StartDate   StartDate AddDays 1                      return counter

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using System   namespace ConsoleApplication1       class Program               static void Main string   args                        DateTime start   new DateTime 2014  1  1               DateTime stop   new DateTime 2014  12  31                int totalWorkingDays   GetNumberOfWorkingDays start  stop                Console WriteLine  There are  0  working days    totalWorkingDays                      private static int GetNumberOfWorkingDays DateTime start  DateTime stop                        TimeSpan interval   stop - start               int totalWeek   interval Days   7              int totalWorkingDays   5   totalWeek               int remainingDays   interval Days   7                for  int i   0  i  lt   remainingDays  i                                  DayOfWeek test    DayOfWeek    int start DayOfWeek   i    7                   if  test  gt   DayOfWeek Monday  amp  amp  test  lt   DayOfWeek Friday                      totalWorkingDays                               return totalWorkingDays

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I ll just share my solution  It worked for me  maybe I just don t notice know that theres a bug  I started by getting the first incomplete week if there s any  a complete week was from sunday for saturday  so if the  int  now DayOfWeek was not 0 Sunday   the first week was incomplete   I just subtract 1 to first weeks count for the first week s saturday then add it to new count   Then I get the last incomplete week  then subtract 1 for it s sunday then add to new count   Then finally  the number of complete weeks multiply by 5 weekdays  was added to new count   public int RemoveNonWorkingDays int numberOfDays                int workingDays   0               int firstWeek   7 -  int  now DayOfWeek               if firstWeek  lt  7                    if firstWeek  gt  numberOfDays                      return numberOfDays                   workingDays    firstWeek-1                  numberOfDays -  firstWeek                              int lastWeek   numberOfDays   7               if lastWeek  gt  0                    numberOfDays -  lastWeek                  workingDays    lastWeek - 1                              workingDays     numberOfDays 7  5               return workingDays

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I was having trouble finding a solid TSQL version of this code  Below is essentially a conversion of the C  code here with addition of the Holiday table which should be used to pre-calculate holidays   CREATE TABLE dbo Holiday       HolidayDt       DATE NOT NULL      Name            NVARCHAR 50  NOT NULL      IsWeekday       BIT NOT NULL      CONSTRAINT PK Holiday PRIMARY KEY  HolidayDt    GO CREATE INDEX IDX Holiday ON Holiday  HolidayDt  IsWeekday   GO  CREATE function dbo GetBusinessDays         FirstDay  datetime        LastDay   datetime    RETURNS INT  AS BEGIN     DECLARE  BusinessDays INT   FullWeekCount INT      SELECT   FirstDay   CONVERT DATETIME CONVERT DATE  FirstDay                LastDay   CONVERT DATETIME CONVERT DATE  LastDay        IF  FirstDay  gt   LastDay         RETURN NULL       SELECT  BusinessDays   DATEDIFF DAY   FirstDay   LastDay    1      SELECT  FullWeekCount    BusinessDays   7       -- find out if there are weekends during the time exceedng the full weeks     IF  BusinessDays  gt    FullWeekCount   7      BEGIN     -- we are here to find out if there is a 1-day or 2-days weekend     -- in the time interval remaining after subtracting the complete weeks         DECLARE  firstDayOfWeek INT   lastDayOfWeek INT          SELECT  firstDayOfWeek   DATEPART DW   FirstDay    lastDayOfWeek   DATEPART DW   LastDay            IF  lastDayOfWeek  lt   firstDayOfWeek                 SELECT  lastDayOfWeek    lastDayOfWeek   7           IF  firstDayOfWeek  lt   6              BEGIN                 IF   lastDayOfWeek  gt   7  --Both Saturday and Sunday are in the remaining time interval                     BEGIN                          SELECT  BusinessDays    BusinessDays - 2                     END                 ELSE IF  lastDayOfWeek gt  6 --Only Saturday is in the remaining time interval                     BEGIN                         SELECT  BusinessDays    BusinessDays - 1                     END              END         ELSE IF  firstDayOfWeek  lt   7 AND  lastDayOfWeek  gt  7 -- Only Sunday is in the remaining time interval         BEGIN              SELECT  BusinessDays    BusinessDays - 1         END     END      -- subtract the weekends during the full weeks in the interval     DECLARE  Holidays INT      SELECT   Holidays   COUNT         FROM    Holiday      WHERE   HolidayDt BETWEEN  FirstDay AND  LastDay      AND     IsWeekday   CAST 1 AS BIT       SELECT  BusinessDays    BusinessDays -   FullWeekCount    FullWeekCount  -- -  Holidays      RETURN  BusinessDays END

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Here is an helper function I wrote for that task  it also returns the count of weekends via the out parameter   if you wish you can customize the  weekend  days in run time for countries that use different weekend days or to include holidays trough the weekendDays   optional parameter    public static int GetNetworkDays DateTime startDate  DateTime endDate out int totalWeekenDays  DayOfWeek   weekendDays   null        if  startDate  gt   endDate                throw new Exception  start date can not be greater then or equel to end date               DayOfWeek   weekends   new DayOfWeek     DayOfWeek Sunday  DayOfWeek Saturday        if  weekendDays    null                weekends   weekendDays             var totaldays    endDate - startDate  TotalDays   1     add one to include the first day to     var counter   0      var workdaysCounter   0      var weekendsCounter   0       for  int i   0  i  lt  totaldays  i                   if  weekends Contains startDate AddDays counter  DayOfWeek                         weekendsCounter                      else                       workdaysCounter                       counter               totalWeekenDays   weekendsCounter      return workdaysCounter

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I used the following code to also take in to account bank holidays   public class WorkingDays       public List lt DateTime gt  GetHolidays                 var client   new WebClient            var json   client DownloadString  https   www gov uk bank-holidays json            var js   new JavaScriptSerializer            var holidays   js Deserialize  lt Dictionary lt string  Holidays gt  gt  json           return holidays  england-and-wales   events Select d   gt  d date  ToList               public int GetWorkingDays DateTime from  DateTime to                var totalDays   0          var holidays   GetHolidays            for  var date   from AddDays 1   date  lt   to  date   date AddDays 1                         if  date DayOfWeek    DayOfWeek Saturday                  amp  amp  date DayOfWeek    DayOfWeek Sunday                  amp  amp   holidays Contains date                   totalDays                       return totalDays           public class Holidays       public string division   get  set        public List lt Event gt  events   get  set       public class Event       public DateTime date   get  set        public string notes   get  set        public string title   get  set        And Unit Tests    TestClass  public class WorkingDays        TestMethod      public void SameDayIsZero                 var service   new WorkingDays             var from   new DateTime 2013  8  12            Assert AreEqual 0  service GetWorkingDays from  from                 TestMethod      public void CalculateDaysInWorkingWeek                 var service   new WorkingDays             var from   new DateTime 2013  8  12           var to   new DateTime 2013  8  16            Assert AreEqual 4  service GetWorkingDays from  to    Mon - Fri   4             Assert AreEqual 1  service GetWorkingDays from  new DateTime 2013  8  13     Mon - Tues   1                TestMethod      public void NotIncludeWeekends                 var service   new WorkingDays             var from   new DateTime 2013  8  9           var to   new DateTime 2013  8  16            Assert AreEqual 5  service GetWorkingDays from  to    Fri - Fri   5             Assert AreEqual 2  service GetWorkingDays from  new DateTime 2013  8  13     Fri - Tues   2            Assert AreEqual 1  service GetWorkingDays from  new DateTime 2013  8  12     Fri - Mon   1                TestMethod      public void AccountForHolidays                 var service   new WorkingDays             var from   new DateTime 2013  8  23            Assert AreEqual 0  service GetWorkingDays from  new DateTime 2013  8  26     Fri - Mon   0             Assert AreEqual 1  service GetWorkingDays from  new DateTime 2013  8  27     Fri - Tues   1

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Here is one very simple solution for this problem  We have starting date  end date and  for loop  for encreasing the day and calculating to see if it s a workday or a weekend by converting to string DayOfWeek   class Program       static void Main string   args                DateTime day   new DateTime            Console Write  Inser your end date  example  01 30 2015               DateTime endDate   DateTime Parse Console ReadLine             int numberOfDays   0          for  day   DateTime Now Date  day Date  lt  endDate Date  day   day Date AddDays 1                         string dayToString   Convert ToString day DayOfWeek               if  dayToString     Saturday   amp  amp  dayToString     Sunday   numberOfDays                      Console WriteLine  Number of working days  not including local holidays  between two dates is   numberOfDays

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This is a generic solution    startdayvalue is day number of start date   weekendday 1 is day numner of week end   day number - MON - 1  TUE - 2      SAT - 6  SUN -7   difference is difference between two dates    Example   Start Date   4 April  2013  End Date   14 April  2013  Difference   10  startdayvalue   4  weekendday 1   7  if SUNDAY is a weekend for you    This will give you number of holidays   No of business day    Difference   1  - holiday1      if  startdayvalue  gt  weekendday 1                 if  difference  gt    7 - startdayvalue    weekendday 1                         holiday1    difference -   7 - startdayvalue    weekendday 1     7              holiday1   holiday1   1                    else                       holiday1   0                      else if  startdayvalue  lt  weekendday 1                 if  difference  gt   weekendday 1 - startdayvalue                         holiday1    difference -  weekendday 1 - startdayvalue     7              holiday1   holiday1   1                    else if  difference     weekendday 1 - startdayvalue                         holiday1   1                    else                       holiday1   0                      else               holiday1   difference   7          holiday1   holiday1   1

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I ve had such a task before and I ve got the solution  I would avoid enumerating all days in between when it s avoidable  which is the case here  I don t even mention creating a bunch of DateTime instances  as I saw in one of the answers above  This is really waste of processing power  Especially in the real world situation  when you have to examine time intervals of several months  See my code  with comments  below            lt summary gt          Calculates number of business days  taking into account           - weekends  Saturdays and Sundays           - bank holidays in the middle of the week          lt  summary gt           lt param name  firstDay  gt First day in the time interval lt  param gt           lt param name  lastDay  gt Last day in the time interval lt  param gt           lt param name  bankHolidays  gt List of bank holidays excluding weekends lt  param gt           lt returns gt Number of business days during the  span  lt  returns gt      public static int BusinessDaysUntil this DateTime firstDay  DateTime lastDay  params DateTime   bankHolidays                firstDay   firstDay Date          lastDay   lastDay Date          if  firstDay  gt  lastDay              throw new ArgumentException  Incorrect last day     lastDay            TimeSpan span   lastDay - firstDay          int businessDays   span Days   1          int fullWeekCount   businessDays   7             find out if there are weekends during the time exceedng the full weeks         if  businessDays  gt  fullWeekCount 7                           we are here to find out if there is a 1-day or 2-days weekend                in the time interval remaining after subtracting the complete weeks             int firstDayOfWeek    int  firstDay DayOfWeek              int lastDayOfWeek    int  lastDay DayOfWeek              if  lastDayOfWeek  lt  firstDayOfWeek                  lastDayOfWeek    7              if  firstDayOfWeek  lt   6                                if  lastDayOfWeek  gt   7    Both Saturday and Sunday are in the remaining time interval                     businessDays -  2                  else if  lastDayOfWeek  gt   6    Only Saturday is in the remaining time interval                     businessDays -  1                            else if  firstDayOfWeek  lt   7  amp  amp  lastDayOfWeek  gt   7    Only Sunday is in the remaining time interval                 businessDays -  1                        subtract the weekends during the full weeks in the interval         businessDays -  fullWeekCount   fullWeekCount              subtract the number of bank holidays during the time interval         foreach  DateTime bankHoliday in bankHolidays                        DateTime bh   bankHoliday Date              if  firstDay  lt   bh  amp  amp  bh  lt   lastDay                  --businessDays                     return businessDays            Edit by Slauma  August 2011  Great answer  There is little bug though  I take the freedom to edit this answer since the answerer is absent since 2009   The code above assumes that DayOfWeek Sunday has the value 7 which is not the case  The value is actually 0  It leads to a wrong calculation if for example firstDay and lastDay are both the same Sunday  The method returns 1 in this case but it should be 0   Easiest fix for this bug  Replace in the code above the lines where firstDayOfWeek and lastDayOfWeek are declared by the following   int firstDayOfWeek   firstDay DayOfWeek    DayOfWeek Sunday        7    int firstDay DayOfWeek  int lastDayOfWeek   lastDay DayOfWeek    DayOfWeek Sunday       7    int lastDay DayOfWeek    Now the result is    Friday to Friday -  1 Saturday to Saturday -  0 Sunday to Sunday -  0 Friday to Saturday -  1 Friday to Sunday -  1 Friday to Monday -  2 Saturday to Monday -  1 Sunday to Monday -  1 Monday to Monday -  1

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Here s yet another idea - this method allows to specify any working week and holidays   The idea here is that we find the core of the date range from the first first working day of the week to the last weekend day of the week   This enables us to calculate the whole weeks easily  without iterating over all of the dates    All we need to do then is to add the working days that fall before the start and end of this core range   public static int CalculateWorkingDays      DateTime startDate       DateTime endDate       IList lt DateTime gt  holidays       DayOfWeek firstDayOfWeek      DayOfWeek lastDayOfWeek           Make sure the defined working days run contiguously     if  lastDayOfWeek  lt  firstDayOfWeek                throw new Exception  Last day of week cannot fall before first day of week                   Create a list of the days of the week that make-up the weekend by working back        from the firstDayOfWeek and forward from lastDayOfWeek to get the start and end        the weekend     var weekendStart   lastDayOfWeek    DayOfWeek Saturday   DayOfWeek Sunday   lastDayOfWeek   1      var weekendEnd   firstDayOfWeek    DayOfWeek Sunday   DayOfWeek Saturday   firstDayOfWeek - 1      var weekendDays   new List lt DayOfWeek gt          var w   weekendStart      do           weekendDays Add w           if  w    weekendEnd  break          w    w    DayOfWeek Saturday    DayOfWeek Sunday   w   1        while  true            Force simple dates - no time     startDate   startDate Date      endDate   endDate Date          Ensure a progessive date range     if  endDate  lt  startDate                var t   startDate          startDate   endDate          endDate   t                setup some working variables and constants     const int daysInWeek   7               yeah - really      var actualStartDate   startDate        this will end up on startOfWeek boundary     var actualEndDate   endDate            this will end up on weekendEnd boundary     int workingDaysInWeek   daysInWeek - weekendDays Count       int workingDays   0            the result we are trying to find     int leadingDays   0            the number of working days leading up to the firstDayOfWeek boundary     int trailingDays   0           the number of working days counting back to the weekendEnd boundary         Calculate leading working days        if we aren t on the firstDayOfWeek we need to step forward to the nearest     if  startDate DayOfWeek    firstDayOfWeek                var d   startDate          do               if  d DayOfWeek    firstDayOfWeek    d  gt   endDate                                actualStartDate   d                  break                              if   weekendDays Contains d DayOfWeek                                 leadingDays                              d   d AddDays 1             while true                 Calculate trailing working days        if we aren t on the weekendEnd we step back to the nearest     if  endDate  gt   actualStartDate  amp  amp  endDate DayOfWeek    weekendEnd                var d   endDate          do               if  d DayOfWeek    weekendEnd    d  lt  actualStartDate                                actualEndDate   d                  break                              if   weekendDays Contains d DayOfWeek                                 trailingDays                              d   d AddDays -1             while true                 Calculate the inclusive number of days between the actualStartDate and the actualEndDate     var coreDays    actualEndDate - actualStartDate  Days   1      var noWeeks    coreDays   daysInWeek          add together leading  core and trailing days     workingDays     noWeeks   workingDaysInWeek      workingDays    leadingDays      workingDays    trailingDays          Finally remove any holidays that fall within the range      if  holidays    null                workingDays -  holidays Count h   gt  h  gt   startDate  amp  amp   h  lt   endDate               return workingDays

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Based on the comment marked as answer and patch recommended   as well as -  This version wants to convert the Days to Business-Hours     Considers Same day hours as well         lt summary gt          Calculates number of business days  taking into account           - weekends  Saturdays and Sundays           - bank holidays in the middle of the week          lt  summary gt           lt param name  firstDay  gt First day in the time interval lt  param gt           lt param name  lastDay  gt Last day in the time interval lt  param gt           lt param name  bankHolidays  gt List of bank holidays excluding weekends lt  param gt           lt returns gt Number of business hours during the  span  lt  returns gt      public static int BusinessHoursUntil DateTime firstDay  DateTime lastDay  params DateTime   bankHolidays                var original firstDay   firstDay          var original lastDay   lastDay          firstDay   firstDay Date          lastDay   lastDay Date          if  firstDay  gt  lastDay              return -1       throw new ArgumentException  Incorrect last day     lastDay            TimeSpan span   lastDay - firstDay          int businessDays   span Days   1          int fullWeekCount   businessDays   7             find out if there are weekends during the time exceedng the full weeks         if  businessDays  gt  fullWeekCount   7                           we are here to find out if there is a 1-day or 2-days weekend                in the time interval remaining after subtracting the complete weeks             int firstDayOfWeek   firstDay DayOfWeek    DayOfWeek Sunday   7    int firstDay DayOfWeek              int lastDayOfWeek   lastDay DayOfWeek    DayOfWeek Sunday   7    int lastDay DayOfWeek               if  lastDayOfWeek  lt  firstDayOfWeek                  lastDayOfWeek    7              if  firstDayOfWeek  lt   6                                if  lastDayOfWeek  gt   7    Both Saturday and Sunday are in the remaining time interval                     businessDays -  2                  else if  lastDayOfWeek  gt   6    Only Saturday is in the remaining time interval                     businessDays -  1                            else if  firstDayOfWeek  lt   7  amp  amp  lastDayOfWeek  gt   7    Only Sunday is in the remaining time interval                 businessDays -  1                        subtract the weekends during the full weeks in the interval         businessDays -  fullWeekCount   fullWeekCount           if  bankHolidays    null  amp  amp  bankHolidays Any                             subtract the number of bank holidays during the time interval             foreach  DateTime bankHoliday in bankHolidays                                DateTime bh   bankHoliday Date                  if  firstDay  lt   bh  amp  amp  bh  lt   lastDay                      --businessDays                                   int total business hours   0          if  firstDay Date    lastDay Date             If on the same day  go granular with Hours from the Orginial  Day values             total business hours    int  original lastDay - original firstDay  TotalHours                    else            Convert Business-Days to TotalHours             total business hours    int  firstDay AddDays businessDays  AddHours firstDay Hour  - firstDay  TotalHours                    return total business hours

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I searched a lot for a  easy to digest  algorithm to calculate the working days between 2 dates  and also to exclude the national holidays  and finally I decide to go with this approach   public static int NumberOfWorkingDaysBetween2Dates DateTime start DateTime due IEnumerable lt DateTime gt  holidays                        var dic   new Dictionary lt DateTime  DayOfWeek gt                 var totalDays    due - start  Days              for  int i   0  i  lt  totalDays   1  i                                  if   holidays Any x   gt  x    start AddDays i                        dic Add start AddDays i   start AddDays i  DayOfWeek                              return dic Where x   gt  x Value    DayOfWeek Saturday  amp  amp  x Value    DayOfWeek Sunday  Count                 Basically I wanted to go with each date and evaluate my conditions    Is not Saturday  Is not Sunday  Is not national holiday   but also I wanted to avoid iterating dates    By running and measuring the time need it to evaluate 1 full year  I go the following result    static void Main string   args                        var start   new DateTime 2017  1  1               var due   new DateTime 2017  12  31                var sw   Stopwatch StartNew                var days   NumberOfWorkingDaysBetween2Dates start  due NationalHolidays                 sw Stop                 Console WriteLine   Total working days    days  --- time   sw Elapsed                 Console ReadLine                    result is                Total working days   249-- - time  00 00 00 0269087             Edit  a new method more simple    public static int ToBusinessWorkingDays this DateTime start  DateTime due  DateTime   holidays                        return Enumerable Range 0   due - start  Days                               Select a   gt  start AddDays a                                Where a   gt  a DayOfWeek    DayOfWeek Sunday                               Where a   gt  a DayOfWeek    DayOfWeek Saturday                               Count a   gt   holidays Any x   gt  x    a

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Check this  1  https   github com yatishbalaji moment-working-days readme  2  https   www npmjs com package moment-working-days  It allows you to calculate working days  considering sequence of date s   You can customize the week off days  and also declare custom dates for holidays  eg  public holidays  to exclude them from being counted as working day s

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Works and without loops  This method doesn t use any loops and is actually quite simple  It expands the date range to full weeks since we know that each week has 5 business days  It then uses a lookup table to find the number of business days to subtract from the start and end to get the right result  I ve expanded out the calculation to help show what s going on  but the whole thing could be condensed into a single line if needed   Anyway  this works for me and so I thought I d post it here in case it might help others  Happy coding    Calculation    t   Total number of days between dates  1 if min   max   a   b   Extra days needed to expand total to full weeks  k   1 4 is number of weekdays per week  i e    t   7    5 c   Number of weekdays to subtract from the total  m   A lookup table used to find the value of  c  for each day of the week   Culture  Code assumes a Monday to Friday work week  For other cultures  such as Sunday to Thursday  you ll need to offset the dates prior to calculation    Method  public int Weekdays DateTime min  DateTime max                    if  min Date  gt  max Date  throw new Exception  Invalid date span            var t    max AddDays 1  Date - min Date  TotalDays          var a    int  min DayOfWeek          var b   6 -  int  max DayOfWeek          var k   1 4          var m   new int   0  0  1  2  3  4  5            var c   m a    m b           return  int   t   a   b    k  - c

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I came up with the following solution  var dateStart   new DateTime 2019 01 10   var dateEnd   new DateTime 2019 01 31    var timeBetween    dateEnd - dateStart  TotalDays   1  int numberOf7DayWeeks    int  timeBetween   7   int numberOfWeekendDays   numberOf7DayWeeks   2  int workingDays   int   timeBetween - numberOfWeekendDays    if dateStart DayOfWeek    DayOfWeek Saturday    dateEnd DayOfWeek    DayOfWeek Sunday       workingDays - 2           if dateStart DayOfWeek    DayOfWeek Sunday    dateEnd DayOfWeek    DayOfWeek Saturday       workingDays - 1

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Since I can t comment  There is one more issue with the accepted solution where bank holidays are subtracted even when they are situated in the weekend  Seeing how other input is checked  it is only fitting that this is as well   The foreach should therefore be          subtract the number of bank holidays during the time interval     foreach  DateTime bankHoliday in bankHolidays                DateTime bh   bankHoliday Date              Do not subtract bank holidays when they fall in the weekend to avoid double subtraction         if  bh DayOfWeek    DayOfWeek Saturday    bh DayOfWeek    DayOfWeek Sunday                  continue           if  firstDay  lt   bh  amp  amp  bh  lt   lastDay              --businessDays

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Here s a quick sample code  It s a class method  so will only work inside of your class  If you want it to be static  change the signature to private static  or public static        private IEnumerable lt DateTime gt  GetWorkingDays DateTime sd  DateTime ed                for  var d   sd  d  lt   ed  d   d AddDays 1               if  d DayOfWeek    DayOfWeek Saturday  amp  amp  d DayOfWeek    DayOfWeek Sunday                  yield return d          This method creates a loop variable d  initializes it to the start day  sd  then increments by one day each iteration  d   d AddDays 1     It returns the desired values using yield  which creates an iterator  The cool thing about iterators is that they don t hold all of the values of the IEnumerable in memory  only calling each one sequentially  This means that you can call this method from the dawn of time to now without having to worry about running out of memory

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I believe this could be a simpler way       public int BusinessDaysUntil DateTime start  DateTime end  params DateTime   bankHolidays                int tld    int   end - start  TotalDays    1    including end day         int not buss day   2    tld   7     Saturday and Sunday         int rest   tld   7    rest           if  rest  gt  0                        int tmp    int start DayOfWeek - 1   rest              if  tmp    6    start DayOfWeek    DayOfWeek Sunday  not buss day    else if  tmp  gt  6  not buss day    2                     foreach  DateTime bankHoliday in bankHolidays                        DateTime bh   bankHoliday Date              if    bh DayOfWeek    DayOfWeek Saturday    bh DayOfWeek    DayOfWeek Sunday   amp  amp   start  lt   bh  amp  amp  bh  lt   end                                 not buss day                                    return tld - not buss day

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Here s some code for that purpose  with swedish holidays but you can adapt what holidays to count  Note that I added a limit you might want to remove  but it was for a web-based system and I didnt want anyone to enter some huge date to hog the process    public static int GetWorkdays DateTime from  DateTime to                int limit   9999          int counter   0          DateTime current   from          int result   0           if  from  gt  to                        DateTime temp   from              from   to              to   temp                     if  from  gt   to                        return 0                      while  current  lt   to  amp  amp  counter  lt  limit                        if  IsSwedishWorkday current                                 result                              current   current AddDays 1               counter                       return result              public static bool IsSwedishWorkday DateTime date                return   IsSwedishHoliday date   amp  amp  date DayOfWeek    DayOfWeek Saturday  amp  amp  date DayOfWeek    DayOfWeek Sunday              public static bool IsSwedishHoliday DateTime date                return           IsSameDay GetEpiphanyDay date Year   date             IsSameDay GetMayDay date Year   date             IsSameDay GetSwedishNationalDay date Year   date             IsSameDay GetChristmasDay date Year   date             IsSameDay GetBoxingDay date Year   date             IsSameDay GetGoodFriday date Year   date             IsSameDay GetAscensionDay date Year   date             IsSameDay GetAllSaintsDay date Year   date             IsSameDay GetMidsummersDay date Year   date             IsSameDay GetPentecostDay date Year   date             IsSameDay GetEasterMonday date Year   date             IsSameDay GetNewYearsDay date Year   date             IsSameDay GetEasterDay date Year   date                           Trettondagen     public static DateTime GetEpiphanyDay int year                return new DateTime year  1  6                 F  rsta maj     public static DateTime GetMayDay int year                return new DateTime year 5 1                 Juldagen     public static DateTime GetSwedishNationalDay int year                return new DateTime year  6  6                  Juldagen     public static DateTime GetNewYearsDay int year                return new DateTime year 1 1                 Juldagen     public static DateTime GetChristmasDay int year                return new DateTime year 12 25                 Annandag jul     public static DateTime GetBoxingDay int year                return new DateTime year  12  26                  L  ngfredagen     public static DateTime GetGoodFriday int year                return GetEasterDay year  AddDays -3                 Kristi himmelsf  rdsdag     public static DateTime GetAscensionDay int year                return GetEasterDay year  AddDays 5 7 4                 Midsommar     public static DateTime GetAllSaintsDay int year                DateTime result   new DateTime year 10 31           while  result DayOfWeek    DayOfWeek Saturday                        result   result AddDays 1                     return result                Midsommar     public static DateTime GetMidsummersDay int year                DateTime result   new DateTime year  6  20           while  result DayOfWeek    DayOfWeek Saturday                        result   result AddDays 1                     return result                Pingstdagen     public static DateTime GetPentecostDay int year                return GetEasterDay year  AddDays 7   7                 Annandag p  sk     public static DateTime GetEasterMonday int year                return GetEasterDay year  AddDays 1             public static DateTime GetEasterDay int y                double c          double n          double k          double i          double j          double l          double m          double d          c   System Math Floor y   100 0           n   y - 19   System Math Floor y   19 0           k   System Math Floor  c - 17    25 0           i   c - System Math Floor c   4  - System Math Floor  c - k    3    19   n   15          i   i - 30   System Math Floor i   30           i   i - System Math Floor i   28     1 - System Math Floor i   28    System Math Floor 29    i   1     System Math Floor  21 - n    11            j   y   System Math Floor y   4 0    i   2 - c   System Math Floor c   4           j   j - 7   System Math Floor j   7           l   i - j          m   3   System Math Floor  l   40    44     month         d   l   28 - 31   System Math Floor m   4     day          double days     m    3    d   d   31            DateTime result   new DateTime y  3  1  AddDays days-1            return result

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public static int CalculateBusinessDaysInRange this DateTime startDate  DateTime endDate  params DateTime   holidayDates        endDate   endDate Date      if startDate  gt  endDate          throw new ArgumentException  The end date can not be before the start date    nameof endDate        int accumulator   0      DateTime itterator   startDate Date      do                if itterator DayOfWeek    DayOfWeek Saturday  amp  amp  itterator DayOfWeek    DayOfWeek Sunday  amp  amp   holidayDates Any hol   gt  hol Date    itterator             accumulator                 while  itterator   itterator AddDays 1   Date  lt   endDate       return accumulator     I m only posting this because despite all of the excellent answers that have been given  none of the math made sense to me  This is definitely a KISS method that should work and be fairly maintainable  Granted if you are calculating ranges that are greater than 2-3 months this will not be the most effective way  We simply determine if it is a Saturday or Sunday or the date is a given holiday date  If it s not we add a business day  If it is then everything is fine   I m sure this could be even more so simplified with LINQ  but this way is much easier to understand

[c#] Calculate the number of business days between two dates?

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