calculating the difference in months between two dates

Question

In C   NET TimeSpan has TotalDays  TotalMinutes  etc  but I can t figure out a formula for total months difference  Variable days per month and leap years keep throwing me off  How can I get TotalMonths   Edit Sorry for not being more clear  I know I can t actually get this from TimeSpan but I thought using TotalDays and TotalMinutes would be a good example to express what I was looking for     except I m trying to get Total Months   Example  Dec 25  2009 - Oct 6  2009   2 TotalMonths  Oct 6th to Nov 5th equals 0 months  On Nov 6th  1 month  On Dec 6th  2 months

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If you want to have a result 1 between 28th Feb and 1st March     DateTime date1  date2  int monthSpan    date2 Year - date1 Year    12   date2 Month - date1 Month

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I realize this is an old question  but      This is relatively painful to do in pure  NET  I d recommend my own Noda Time library  which is particularly designed for things like this   LocalDate start   new LocalDate 2009  10  6   LocalDate end   new LocalDate 2009  12  25   Period period   Period Between start  end   int months   period Months     There are other options  e g  if you only want a count of months even across years  you d use Period period   Period Between start  end  PeriodUnits Months

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http   www astro uu nl  strous AA en reken juliaansedag html  If you can get the time converted from a Gregorian Date into Julian day number  you can just create an operator to do comparisons of the zulian day number  which can be type double to get months  days  seconds  etc  Check out the above link for an algorithm for converting from Gregorian to Julian

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If you re dealing with months and years you need something that knows how many days each month has and which years are leap years   Enter the Gregorian Calendar  and other culture-specific Calendar implementations    While Calendar doesn t provide methods to directly calculate the difference between two points in time  it does have methods such as   DateTime AddWeeks DateTime time  int weeks  DateTime AddMonths DateTime time  int months  DateTime AddYears DateTime time  int years

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My take on this answer also uses an extension method  but it can return a positive or negative result   public static int MonthsBefore this DateTime dt1  DateTime dt2         DateTime early  DateTime late  bool dt2After    dt2  gt  dt1    dt1 dt2 true     dt2 dt1 false       DateTime tmp     Save the result so we don t repeat work     int months   1      while   tmp   early AddMonths 1    lt   late                early   tmp          months              return  months-1   dt2After   1   -1       A couple tests      Just under 1 month s diff Assert AreEqual 0  new DateTime 2014  1  1  MonthsBefore new DateTime 2014  1  31        Just over 1 month s diff Assert AreEqual 1  new DateTime 2014  1  1  MonthsBefore new DateTime 2014  2  2            Past date returns NEGATIVE Assert AreEqual -6  new DateTime 2012  1  1  MonthsBefore new DateTime 2011  6  10

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Here s how we did it  int DifferenceInMonth DateTime startDate  DateTime endDate        long ToTicks DateTime date    gt  new DateTimeOffset date  Ticks      var daysPerMonth   30 4      return  int Math Round  ToTicks endDate  - ToTicks startDate     TimeSpan TicksPerDay   daysPerMonth

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Here is my contribution to get difference in Months that I ve found to be accurate   namespace System        public static class DateTimeExtensions                 public static Int32 DiffMonths  this DateTime start  DateTime end                           Int32 months   0               DateTime tmp   start                while   tmp  lt  end                                   months                     tmp   tmp AddMonths  1                                 return months                      Usage   Int32 months   DateTime Now DiffMonths  DateTime Now AddYears  5        You can create another method called DiffYears and apply exactly the same logic as above and AddYears instead of AddMonths in the while loop

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I ve written a very simple extension method on DateTime and DateTimeOffset to do this  I wanted it to work exactly like a TotalMonths property on TimeSpan would work  i e  return the count of complete months between two dates  ignoring any partial months  Because it s based on DateTime AddMonths   it respects different month lengths and returns what a human would understand as a period of months    Unfortunately you can t implement it as an extension method on TimeSpan because that doesn t retain knowledge of the actual dates used  and for months they re important    The code and tests are both available on GitHub  The code is very simple   public static int GetTotalMonthsFrom this DateTime dt1  DateTime dt2        DateTime earlyDate    dt1  gt  dt2    dt2 Date   dt1 Date      DateTime lateDate    dt1  gt  dt2    dt1 Date   dt2 Date          Start with 1 month s difference and keep incrementing        until we overshoot the late date     int monthsDiff   1      while  earlyDate AddMonths monthsDiff   lt   lateDate                monthsDiff               return monthsDiff - 1      And it passes all these unit test cases      Simple comparison Assert AreEqual 1  new DateTime 2014  1  1  GetTotalMonthsFrom new DateTime 2014  2  1        Just under 1 month s diff Assert AreEqual 0  new DateTime 2014  1  1  GetTotalMonthsFrom new DateTime 2014  1  31        Just over 1 month s diff Assert AreEqual 1  new DateTime 2014  1  1  GetTotalMonthsFrom new DateTime 2014  2  2        31 Jan to 28 Feb Assert AreEqual 1  new DateTime 2014  1  31  GetTotalMonthsFrom new DateTime 2014  2  28        Leap year 29 Feb to 29 Mar Assert AreEqual 1  new DateTime 2012  2  29  GetTotalMonthsFrom new DateTime 2012  3  29        Whole year minus a day Assert AreEqual 11  new DateTime 2012  1  1  GetTotalMonthsFrom new DateTime 2012  12  31        Whole year Assert AreEqual 12  new DateTime 2012  1  1  GetTotalMonthsFrom new DateTime 2013  1  1        29 Feb  leap  to 28 Feb  non-leap  Assert AreEqual 12  new DateTime 2012  2  29  GetTotalMonthsFrom new DateTime 2013  2  28        100 years Assert AreEqual 1200  new DateTime 2000  1  1  GetTotalMonthsFrom new DateTime 2100  1  1        Same date Assert AreEqual 0  new DateTime 2014  8  5  GetTotalMonthsFrom new DateTime 2014  8  5        Past date Assert AreEqual 6  new DateTime 2012  1  1  GetTotalMonthsFrom new DateTime 2011  6  10

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There are not a lot of clear answers on this because you are always assuming things   This solution calculates between two dates the months between assuming you want to save the day of month for comparison   meaning that the day of the month is considered in the calculation   Example  if you have a date of 30 Jan 2012  29 Feb 2012 will not be a month but 01 March 2013 will   It s been tested pretty thoroughly  probably will clean it up later as we use it  and takes in two dates instead of a Timespan  which is probably better  Hope this helps out anyone else   private static int TotalMonthDifference DateTime dtThis  DateTime dtOther        int intReturn   0      bool sameMonth   false       if  dtOther Date  lt  dtThis Date    used for an error catch in program  returns -1         intReturn--       int dayOfMonth   dtThis Day    captures the month of day for when it adds a month and doesn t have that many days     int daysinMonth   0    used to caputre how many days are in the month      while  dtOther Date  gt  dtThis Date    while Other date is still under the other               dtThis   dtThis AddMonths 1     as we loop  we just keep adding a month for testing         daysinMonth   DateTime DaysInMonth dtThis Year  dtThis Month     grabs the days in the current tested month          if  dtThis Day    dayOfMonth    Example 30 Jan 2013 will go to 28 Feb when a month is added  so when it goes to march it will be 28th and not 30th                       if  daysinMonth  lt  dayOfMonth     uses day in month max if can t set back to day of month                 dtThis AddDays daysinMonth - dtThis Day               else                 dtThis AddDays dayOfMonth - dtThis Day                     if    dtOther Year    dtThis Year   amp  amp   dtOther Month    dtThis Month      If the loop puts it in the same month and year                       if  dtOther Day  gt   dayOfMonth    check to see if it is the same day or later to add one to month                 intReturn                sameMonth   true    sets this to cancel out of the normal counting of month                   if    sameMonth  amp  amp  dtOther Date  gt  dtThis Date    so as long as it didn t reach the same month  or if i started in the same month  one month ahead  add a month              intReturn              return intReturn    return month

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DateTime start   new DateTime 2003  12  25   DateTime end   new DateTime 2009  10  6   int compMonth    end Month   end Year   12  -  start Month   start Year   12   double daysInEndMonth    end - end AddMonths 1   Days  double months   compMonth    start Day - end Day    daysInEndMonth

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Combing two of the answers above  another extension method is   public static int ElapsedMonths this DateTime date1  DateTime date2        DateTime earlierDate    date1  gt  date2    date2   date1      DateTime laterDate    date1  gt  date2    date1   date2      var eMonths    laterDate Month - earlierDate Month    12    laterDate Year - earlierDate Year  -                                                earlierDate Day  gt  laterDate Day    1   0       return eMonths       Thanks to  AdamRobinson and  MarkWhittaker

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Calculate no of months between 2 dates    date1    2017-01-20    date2    2019-01-20     ts1   strtotime  date1    ts2   strtotime  date2     year1   date  Y    ts1    year2   date  Y    ts2     month1   date  m    ts1    month2   date  m    ts2    echo  joining months      year2 -  year1    12      month2 -  month1

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The accepted answer is strongly incorrect  For these dates  ldate   2020-08-30 and rdate   2020-08-01  we have one month  but the accepted answer returns 0  For these dates  ldate   2020-08-30 and rdate   2020-10-01  we have three months  but the accepted answer returns -2  Here is the correct method  maybe not the unique method  but correct  to calculate the quantity of months between two dates   You don t have to check which date is lower than other   An interval from the first day to the last day of month is counted as a month    public static int GetMontsBetween DateTime date1  DateTime date2            int monthCount   0        int direction   date1  lt  date2   1   -1        date2   date2 AddDays direction          while  date1 Year    date2 Year    date1 Month    date2 Month                    date1   date1 AddMonths direction             monthCount                   return monthCount

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The method returns a list that contains 3 element first is year  second is month and end element is day   public static List lt int gt  GetDurationInEnglish DateTime from  DateTime to                try                       if  from  gt  to                  return null               var fY   from Year              var fM   from Month              var fD   DateTime DaysInMonth fY  fM                var tY   to Year              var tM   to Month              var tD   DateTime DaysInMonth tY  tM                int dY   0              int dM   0              int dD   0               if  fD  gt  tD                                tM--                   if  tM  lt   0                                        tY--                      tM   12                      tD    DateTime DaysInMonth tY  tM                                     else                                       tD    DateTime DaysInMonth tY  tM                                               dD   tD - fD               if  fM  gt  tM                                tY--                   tM    12                            dM   tM - fM               dY   tY - fY               return new List lt int gt      dY  dM  dD                      catch  Exception exception                          todo  log exception with parameters in db              return null

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The problem with months is that it isn t really a simple measure - they aren t constant size  You would need to define your rules for what you want to include  and work from there  For example 1 Jan to 1 Feb - you could argue 2 months are involved there  or you could say that is one month  Then what about  1 Jan 20 00  to  1 Feb 00 00  - that isn t quite an entire full month  Is that 0  1  what about the other way around  1 Jan 00 00 to 1 Feb 20 00     1  2   First define the rules  then you ll have to code it yourself  I m afraid

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There is no built in way to do this accurately in idiomatic-c   There are some workarounds  such as this CodeProject example that people have coded though

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Old question I know  but might help someone  I ve used  Adam accepted answer above  but then checked if the difference is 1 or -1 then check to see if it is a full calendar month s difference   So 21 07 55 and 20 08 55 would not be a full month  but 21 07 55 and 21 07 55 would be        lt summary gt      Amended date of birth cannot be greater than or equal to one month either side of original date of birth       lt  summary gt       lt param name  dateOfBirth  gt Date of birth user could have amended  lt  param gt       lt param name  originalDateOfBirth  gt Original date of birth to compare against  lt  param gt       lt returns gt  lt  returns gt  public JsonResult ValidateDateOfBirth string dateOfBirth  string originalDateOfBirth        DateTime dob  originalDob      bool isValid   false       if  DateTime TryParse dateOfBirth  out dob   amp  amp  DateTime TryParse originalDateOfBirth  out originalDob                 int diff     dob Month - originalDob Month    12    dob Year - originalDob Year             switch  diff                        case 0                     We re on the same month  so ok                  isValid   true                  break              case -1                     The month is the previous month  so check if the date makes it a calendar month out                  isValid    dob Day  gt  originalDob Day                   break              case 1                     The month is the next month  so check if the date makes it a calendar month out                  isValid    dob Day  lt  originalDob Day                   break              default                     Either zero or greater than 1 month difference  so not ok                  isValid   false                  break                    if   isValid              return Json  Date of Birth cannot be greater than one month either side of the date we hold    JsonRequestBehavior AllowGet             else               return Json  Date of Birth is invalid    JsonRequestBehavior AllowGet             return Json true  JsonRequestBehavior AllowGet

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Maybe you don t want to know about month fractions  What about this code     public static class DateTimeExtensions       public static int TotalMonths this DateTime start  DateTime end                return  start Year   12   start Month  -  end Year   12   end Month                Console WriteLine         DateTime Now TotalMonths             DateTime Now AddMonths -1        prints  1

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You need to work it out yourself off the datetimes  How you deal with the stub days at the end will depend on what you want to use it for   One method would be to count month and then correct for days at the end  Something like      DateTime start   new DateTime 2003  12  25      DateTime end   new DateTime 2009  10  6      int compMonth    end Month   end Year   12  -  start Month   start Year   12      double daysInEndMonth    end - end AddMonths 1   Days     double months   compMonth    start Day - end Day    daysInEndMonth

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You won t be able to get that from a TimeSpan  because a  month  is a variable unit of measure  You ll have to calculate it yourself  and you ll have to figure out how exactly you want it to work    For example  should dates like July 5  2009 and August 4  2009 yield one month or zero months difference  If you say it should yield one  then what about July 31  2009 and August 1  2009  Is that a month  Is it simply the difference of the Month values for the dates  or is it more related to an actual span of time  The logic for determining all of these rules is non-trivial  so you ll have to determine your own and implement the appropriate algorithm   If all you want is simply a difference in the months--completely disregarding the date values--then you can use this   public static int MonthDifference this DateTime lValue  DateTime rValue        return  lValue Month - rValue Month    12    lValue Year - rValue Year       Note that this returns a relative difference  meaning that if rValue is greater than lValue  then the return value will be negative  If you want an absolute difference  you can use this   public static int MonthDifference this DateTime lValue  DateTime rValue        return Math Abs  lValue Month - rValue Month    12    lValue Year - rValue Year

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Below is actually the most accurate way you can do it  since the definition of  1 Month  changes depending on which month it is  and non of the other answers take this into account  If you want more information about the issue which is not built into the framework  you can read this post  A Real Timespan Object With  Years  amp   Months   however  reading that post isn t necessary to understand and use the function below  it works 100   without the inherent inaccuracies of the approximation others love to use - and feel free to replace the  ReverseIt function with the built-in  Reverse function you may have on your framework  it s just here for completeness    Please note that you can get any number of dates times accuracy  seconds  amp  minutes  or seconds  minutes and days  anywhere up to years  which would contain 6 parts segments   If you specify top two and it s over a year old  it will return  1 year and 3 months ago  and won t return the rest because you ve requested two segments  if it s only a few hours old  then it will only return  2 hours and 1 minute ago   Of course  same rules apply if you specify 1  2  3  4  5 or 6 segmets  maxes out at 6 because seconds  minutes  hours  days  months  years only make 6 types   It will also correct grammer issues like  minutes  vs  minute  depending on if it s 1 minute or more  same for all types  and the  string  generated will always be grammatically correct   Here are some examples for use  bAllowSegments identifies how many segments to show    ie  if 3  then return string would be  as an example       3 years  2 months and 13 days   won t include hours  minutes and seconds as the top 3 time categories are returned   if however  the date was a newer date  such as something a few days ago  specifying the same segments  3  will return  4 days  1 hour and 13 minutes ago  instead  so it takes everything into account   if bAllowSegments is 2 it would return  3 years and 2 months  and if 6  maximum value  would return  3 years  2 months  13 days  13 hours  29 minutes and 9 seconds   but  be reminded that it will NEVER RETURN something like this  0 years  0 months  0 days  3 hours  2 minutes and 13 seconds ago  as it understands there is no date data in the top 3 segments and ignores them  even if you specify 6 segments  so don t worry     Of course  if there is a segment with 0 in it  it will take that into account when forming the string  and will display as  3 days and 4 seconds ago  and ignoring the  0 hours  part  Enjoy and please comment if you like    Public Function RealTimeUntilNow ByVal dt As DateTime  Optional ByVal bAllowSegments As Byte   2  As String     bAllowSegments identifies how many segments to show    ie  if 3  then return string would be  as an example          3 years  2 months and 13 days  the top 3 time categories are returned  if bAllowSegments is 2 it would return      3 years and 2 months  and if 6  maximum value  would return  3 years  2 months  13 days  13 hours  29 minutes and 9 seconds    Dim rYears  rMonths  rDays  rHours  rMinutes  rSeconds As Int16   Dim dtNow   DateTime Now   Dim daysInBaseMonth   Date DaysInMonth dt Year  dt Month     rYears   dtNow Year - dt Year   rMonths   dtNow Month - dt Month   If rMonths  lt  0 Then rMonths    12   rYears -  1   add 1 year to months  and remove 1 year from years    rDays   dtNow Day - dt Day   If rDays  lt  0 Then rDays    daysInBaseMonth   rMonths -  1   rHours   dtNow Hour - dt Hour   If rHours  lt  0 Then rHours    24   rDays -  1   rMinutes   dtNow Minute - dt Minute   If rMinutes  lt  0 Then rMinutes    60   rHours -  1   rSeconds   dtNow Second - dt Second   If rSeconds  lt  0 Then rSeconds    60   rMinutes -  1      this is the display functionality   Dim sb As StringBuilder   New StringBuilder     Dim iSegmentsAdded As Int16   0    If rYears  gt  0 Then sb Append rYears    sb Append   year   amp  If rYears  lt  gt  1   s        amp          iSegmentsAdded    1   If bAllowSegments   iSegmentsAdded Then GoTo parseAndReturn    If rMonths  gt  0 Then sb AppendFormat rMonths    sb Append   month   amp  If rMonths  lt  gt  1   s        amp          iSegmentsAdded    1   If bAllowSegments   iSegmentsAdded Then GoTo parseAndReturn    If rDays  gt  0 Then sb Append rDays    sb Append   day   amp  If rDays  lt  gt  1   s        amp          iSegmentsAdded    1   If bAllowSegments   iSegmentsAdded Then GoTo parseAndReturn    If rHours  gt  0 Then sb Append rHours    sb Append   hour   amp  If rHours  lt  gt  1   s        amp          iSegmentsAdded    1   If bAllowSegments   iSegmentsAdded Then GoTo parseAndReturn    If rMinutes  gt  0 Then sb Append rMinutes    sb Append   minute   amp  If rMinutes  lt  gt  1   s        amp          iSegmentsAdded    1   If bAllowSegments   iSegmentsAdded Then GoTo parseAndReturn    If rSeconds  gt  0 Then sb Append rSeconds    sb Append   second   amp  If rSeconds  lt  gt  1   s        amp        iSegmentsAdded    1  parseAndReturn       if the string is entirely empty  that means it was just posted so its less than a second ago  and an empty string getting passed will cause an error     so we construct our own meaningful string which will still fit into the  Posted   ago   syntax       If sb ToString      Then sb Append  less than 1 second      Return ReplaceLast sb ToString TrimEnd           ToString         and     End Function   Of course  you will need a  ReplaceLast  function  which takes a source string  and an argument specifying what needs to be replaced  and another arg specifying what you want to replace it with  and it only replaces the last occurance of that string    i ve included my one if you don t have one or dont want to implement it  so here it is  it will work  as is  with no modification needed  I know the reverseit function is no longer needed  exists in  net  but the ReplaceLast and the ReverseIt func are carried over from the pre- net days  so please excuse how dated it may look  still works 100  tho  been using em for over ten years  can guarante they are bug free         cheers    lt Extension   gt     Public Function ReplaceLast ByVal sReplacable As String  ByVal sReplaceWhat As String  ByVal sReplaceWith As String  As String        let empty string arguments run  incase we dont know if we are sending and empty string or not       sReplacable   sReplacable ReverseIt      sReplacable   Replace sReplacable  sReplaceWhat ReverseIt  sReplaceWith ReverseIt    1    only does first item on reversed version       Return sReplacable ReverseIt ToString  End Function    lt Extension   gt     Public Function ReverseIt ByVal strS As String  Optional ByVal n As Integer   -1  As String      Dim strTempX As String       intI As Integer       If n  gt  strS Length Or n   -1 Then n   strS Length       For intI   n To 1 Step -1          strTempX   strTempX   Mid strS  intI  1       Next intI       ReverseIt   strTempX   Right strS  Len strS  - n    End Function

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Way late to the game but I imagine this may be helpful to someone  The majority of people tend to measure month to month by date excluding the fact that months come in different variations  Using that frame of thought I created a one liner which compares the dates for us  Using the the following process    Any   of years over 1 when comparing year will be multiplied by 12  there is no case where this can be equal to less than 1 full year  If the end year is greater we need to evaluate if the current day is greater or equal to the previous day 2A  If the end day is greater or equal we take the current month and then add 12 months subtract the month of the start month 2B  If the end day is less than the start day we perform the the same as above except we add 1 to the start month before subtracting If the end year is not greater we perform the same as 2A 2B  but without adding the 12 months because we do not need to evaluate around the year       DateTime date   new DateTime 2003  11  25       DateTime today   new DateTime 2004  12  26       var time    today Year - date Year  gt  1    today Year - date Year - 1    12   0      today Year  gt  date Year    today Day  gt   date Day   today Month   12 - date Month   today Month   12 -  date Month   1      today Day  gt   date Day   today Month - date Month   today Month -  date Month   1

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If you want the exact number  you can t from just the Timespan  since you need to know which months you re dealing  and whether you re dealing with a leap year  like you said   Either go for an approximate number  or do some fidgetting with the original DateTimes

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This library calculates the difference of months  considering all parts of DateTime      ---------------------------------------------------------------------- public void DateDiffSample       DateTime date1   new DateTime  2009  11  8  7  13  59      Console WriteLine   Date1   0    date1          gt  Date1  08 11 2009 07 13 59   DateTime date2   new DateTime  2011  3  20  19  55  28      Console WriteLine   Date2   0    date2          gt  Date2  20 03 2011 19 55 28    DateDiff dateDiff   new DateDiff  date1  date2          differences   Console WriteLine   DateDiff Years   0    dateDiff Years          gt  DateDiff Years  1   Console WriteLine   DateDiff Quarters   0    dateDiff Quarters          gt  DateDiff Quarters  5   Console WriteLine   DateDiff Months   0    dateDiff Months          gt  DateDiff Months  16   Console WriteLine   DateDiff Weeks   0    dateDiff Weeks          gt  DateDiff Weeks  70   Console WriteLine   DateDiff Days   0    dateDiff Days          gt  DateDiff Days  497   Console WriteLine   DateDiff Weekdays   0    dateDiff Weekdays          gt  DateDiff Weekdays  71   Console WriteLine   DateDiff Hours   0    dateDiff Hours          gt  DateDiff Hours  11940   Console WriteLine   DateDiff Minutes   0    dateDiff Minutes          gt  DateDiff Minutes  716441   Console WriteLine   DateDiff Seconds   0    dateDiff Seconds          gt  DateDiff Seconds  42986489       elapsed   Console WriteLine   DateDiff ElapsedYears   0    dateDiff ElapsedYears          gt  DateDiff ElapsedYears  1   Console WriteLine   DateDiff ElapsedMonths   0    dateDiff ElapsedMonths          gt  DateDiff ElapsedMonths  4   Console WriteLine   DateDiff ElapsedDays   0    dateDiff ElapsedDays          gt  DateDiff ElapsedDays  12   Console WriteLine   DateDiff ElapsedHours   0    dateDiff ElapsedHours          gt  DateDiff ElapsedHours  12   Console WriteLine   DateDiff ElapsedMinutes   0    dateDiff ElapsedMinutes          gt  DateDiff ElapsedMinutes  41   Console WriteLine   DateDiff ElapsedSeconds   0    dateDiff ElapsedSeconds          gt  DateDiff ElapsedSeconds  29      DateDiffSample

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case IntervalType Month      returnValue   start AddMonths -end Month  Month ToString        break  case IntervalType Year      returnValue    start Year - end Year  ToString        break

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The accepted answer works perfectly when you want full months   I needed partial months  This is the solution I came up with for partial months            lt summary gt          Calculate the difference in months          This will round up to count partial months           lt  summary gt           lt param name  lValue  gt  lt  param gt           lt param name  rValue  gt  lt  param gt           lt returns gt  lt  returns gt      public static int MonthDifference DateTime lValue  DateTime rValue                var yearDifferenceInMonths    lValue Year - rValue Year    12          var monthDifference   lValue Month - rValue Month           return yearDifferenceInMonths   monthDifference                 lValue Day  gt  rValue Day                   1   0      If end day is greater than start day  add 1 to round up the partial month         I also needed a year difference with the same need for partial years  Here is the solution I came up with            lt summary gt          Calculate the differences in years          This will round up to catch partial months           lt  summary gt           lt param name  lValue  gt  lt  param gt           lt param name  rValue  gt  lt  param gt           lt returns gt  lt  returns gt      public static int YearDifference DateTime lValue  DateTime rValue                return lValue Year - rValue Year                   lValue Month  gt  rValue Month    Partial month  same year                      1                        lValue Month   rValue Month                         amp  amp   lValue Day  gt  rValue Day      Partial month  same year and month                      1   0

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You will have to define what you mean by TotalMonths to start with  A simple definition puts a month at 30 4 days  365 25   12      Beyond that  any definition including fractions seems useless  and the more common integer value  whole months between dates  also depends on non-standard business rules

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I would do it like this   static int TotelMonthDifference this DateTime dtThis  DateTime dtOther        int intReturn   0       dtThis   dtThis Date AddDays - dtThis Day-1        dtOther   dtOther Date AddDays - dtOther Day-1         while  dtOther Date  gt  dtThis Date                intReturn                 dtThis   dtThis AddMonths 1              return intReturn

[c#] calculating the difference in months between two dates

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