How to get difference between two dates in Year Month Week Day

Question

How to get difference between two dates in Year Month Week Day in an efficient way   eg  difference between two dates is 1 Year  2 Months  3 Weeks  4 Days   Difference represents count of year s   month s   week s  and day s  between two dates

User · Answer

For the correct difference calculation of Years/Months/Weeks, the Calendar of the CultureInfo must be considered:

leap vs. non-leap years
months with different count of days
years with different count of weeks (varying by the first day of week and the calendar week rule)

The DateDiff class of the Time Period Library for .NET respects all these factors:

// ----------------------------------------------------------------------
public void DateDiffSample()
{
  DateTime date1 = new DateTime( 2009, 11, 8, 7, 13, 59 );
  Console.WriteLine( "Date1: {0}", date1 );
  // > Date1: 08.11.2009 07:13:59
  DateTime date2 = new DateTime( 2011, 3, 20, 19, 55, 28 );
  Console.WriteLine( "Date2: {0}", date2 );
  // > Date2: 20.03.2011 19:55:28

  DateDiff dateDiff = new DateDiff( date1, date2 );

  // differences
  Console.WriteLine( "DateDiff.Years: {0}", dateDiff.Years );
  // > DateDiff.Years: 1
  Console.WriteLine( "DateDiff.Quarters: {0}", dateDiff.Quarters );
  // > DateDiff.Quarters: 5
  Console.WriteLine( "DateDiff.Months: {0}", dateDiff.Months );
  // > DateDiff.Months: 16
  Console.WriteLine( "DateDiff.Weeks: {0}", dateDiff.Weeks );
  // > DateDiff.Weeks: 70
  Console.WriteLine( "DateDiff.Days: {0}", dateDiff.Days );
  // > DateDiff.Days: 497
  Console.WriteLine( "DateDiff.Weekdays: {0}", dateDiff.Weekdays );
  // > DateDiff.Weekdays: 71
  Console.WriteLine( "DateDiff.Hours: {0}", dateDiff.Hours );
  // > DateDiff.Hours: 11940
  Console.WriteLine( "DateDiff.Minutes: {0}", dateDiff.Minutes );
  // > DateDiff.Minutes: 716441
  Console.WriteLine( "DateDiff.Seconds: {0}", dateDiff.Seconds );
  // > DateDiff.Seconds: 42986489

  // elapsed
  Console.WriteLine( "DateDiff.ElapsedYears: {0}", dateDiff.ElapsedYears );
  // > DateDiff.ElapsedYears: 1
  Console.WriteLine( "DateDiff.ElapsedMonths: {0}", dateDiff.ElapsedMonths );
  // > DateDiff.ElapsedMonths: 4
  Console.WriteLine( "DateDiff.ElapsedDays: {0}", dateDiff.ElapsedDays );
  // > DateDiff.ElapsedDays: 12
  Console.WriteLine( "DateDiff.ElapsedHours: {0}", dateDiff.ElapsedHours );
  // > DateDiff.ElapsedHours: 12
  Console.WriteLine( "DateDiff.ElapsedMinutes: {0}", dateDiff.ElapsedMinutes );
  // > DateDiff.ElapsedMinutes: 41
  Console.WriteLine( "DateDiff.ElapsedSeconds: {0}", dateDiff.ElapsedSeconds );
  // > DateDiff.ElapsedSeconds: 29

  // description
  Console.WriteLine( "DateDiff.GetDescription(1): {0}", dateDiff.GetDescription( 1 ) );
  // > DateDiff.GetDescription(1): 1 Year
  Console.WriteLine( "DateDiff.GetDescription(2): {0}", dateDiff.GetDescription( 2 ) );
  // > DateDiff.GetDescription(2): 1 Year 4 Months
  Console.WriteLine( "DateDiff.GetDescription(3): {0}", dateDiff.GetDescription( 3 ) );
  // > DateDiff.GetDescription(3): 1 Year 4 Months 12 Days
  Console.WriteLine( "DateDiff.GetDescription(4): {0}", dateDiff.GetDescription( 4 ) );
  // > DateDiff.GetDescription(4): 1 Year 4 Months 12 Days 12 Hours
  Console.WriteLine( "DateDiff.GetDescription(5): {0}", dateDiff.GetDescription( 5 ) );
  // > DateDiff.GetDescription(5): 1 Year 4 Months 12 Days 12 Hours 41 Mins
  Console.WriteLine( "DateDiff.GetDescription(6): {0}", dateDiff.GetDescription( 6 ) );
  // > DateDiff.GetDescription(6): 1 Year 4 Months 12 Days 12 Hours 41 Mins 29 Secs
} // DateDiffSample

DateDiff also calculates the difference of Quarters.

User · Answer

What about using the System Data Linq namespace and its SqlMethods DateDiffMonth method   For example  say   DateTime starDT    01-Jul-2009 12 00 00 AM  DateTime endDT    01-Nov-2009 12 00 00 AM    Then   int monthDiff   System Data Linq SqlClient SqlMethods DateDiffMonth startDT  endDT         4  There are other DateDiff static methods in the SqlMethods class

User · Answer

Use Noda Time   var ld1   new LocalDate 2012  1  1   var ld2   new LocalDate 2013  12  25   var period   Period Between ld1  ld2    Debug WriteLine period              P1Y11M24D    ISO8601 format  Debug WriteLine period Years       1 Debug WriteLine period Months      11 Debug WriteLine period Days        24

User · Answer

If you have to find the difference between originalDate and today   s date  Here is a reliable algorithm without so many condition checks    Declare a intermediateDate variable and initialize to the originalDate Find difference between years  yearDiff  Add yearDiff to intermediateDate and check whether the value is greater than today   s date  If newly obtained intermediateDate   today   s date adjust the  yearDiff and intermediateDate by one  Continue above steps for month and Days    I have used System Data Linq functions to do find the year  month and day differences  Please find c  code below           DateTime todaysDate   DateTime Now          DateTime interimDate   originalDate              Find Year diff         int yearDiff   System Data Linq SqlClient SqlMethods DateDiffYear interimDate  todaysDate           interimDate   interimDate AddYears yearDiff           if  interimDate  gt  todaysDate                        yearDiff -  1              interimDate   interimDate AddYears -1                         Find Month diff         int monthDiff   System Data Linq SqlClient SqlMethods DateDiffMonth interimDate  todaysDate           interimDate   interimDate AddMonths monthDiff           if  interimDate  gt  todaysDate                        monthDiff -  1              interimDate   interimDate AddMonths -1                         Find Day diff         int daysDiff   System Data Linq SqlClient SqlMethods DateDiffDay interimDate  todaysDate

User · Answer

DateTime startTime   DateTime Now   DateTime endTime   DateTime Now AddSeconds  75     TimeSpan span   endTime Subtract   startTime     Console WriteLine   Time Difference  seconds       span Seconds     Console WriteLine   Time Difference  minutes       span Minutes     Console WriteLine   Time Difference  hours       span Hours     Console WriteLine   Time Difference  days       span Days      Output   Time Difference  seconds   15 Time Difference  minutes   1 Time Difference  hours   0 Time Difference  days   0

User · Answer

Well   Jon Skeet  if we re not worried about getting any more granular than days  and still rolling days into larger units rather than having a total day count   as per the OP  it s really not that difficult in C    What makes date math so difficult is that the number of units in each composite unit often changes   Imagine if every 3rd gallon of gas was only 3 quarts  but each 12th was 7  except on Fridays  when     Luckily  dates are just a long ride through the greatest integer function   These crazy exceptions are maddening  unless you ve gone all the way through the wackily-comprised unit  when it s not a big deal any more   If you re born on 12 25 1900  you re still EXACTLY 100 on 12 25 2000  regardless of the leap years or seconds or daylight savings periods you ve been through   As soon as you ve slogged through the percentages that make up the last composite unit  you re back to unity   You ve added one  and get to start over   Which is just to say that if you re doing years to months to days  the only strangely comprised unit is the month  of days    If you need to borrow from the month value to handle a place where you re subtracting more days than you ve got  you just need to know the number of days in the previous month   No other outliers matter     And C  gives that to you in System DateTime DaysInMonth intYear  intMonth     If your Now month is smaller than your Then month  there s no issue   Every year has 12 months    And the same deal if we go more granular    you just need to know how many  small units  are in the last  composite unit    Once you re past  you get another integer value more of  composite unit    Then subtract how many small units you missed starting where you did Then and add back how many of those you went past the composite unit break-off with your Now   So here s what I ve got from my first cut at subtracting two dates   It might work   Hopefully useful      EDIT  Changed NewMonth   OldMonth check to NewMonth    OldMonth  as we don t need to borrow one if the Months are the same  ditto for days    That is  Nov 11 2011 minus Nov 9 2010 was giving -1 year  12 months  2 days  ie  2 days  but the royal we borrowed when royalty didn t need to      EDIT  Had to check for Month   Month when we needed to borrow days to subtract a dteThen Day from dteNow Day  amp  dteNow Day  lt  dteThen Day  as we had to subtract a year to get 11 months and the extra days   Okay  so there are a few outliers     D  I think I m close now    private void Form1 Load object sender  EventArgs e    DateTime dteThen   DateTime Parse  3 31 2010    DateTime dteNow   DateTime Now   int intDiffInYears   0  int intDiffInMonths   0  int intDiffInDays   0    if  dteNow Month  gt   dteThen Month        if  dteNow Day  gt   dteThen Day             this is a best case  easy subtraction situation         intDiffInYears   dteNow Year - dteThen Year          intDiffInMonths   dteNow Month - dteThen Month          intDiffInDays   dteNow Day - dteThen Day            else            else we need to substract one from the month diff  borrow the one             and days get wacky              Watch for the outlier of Month   Month with DayNow  lt  DayThen  as then we ve             got to subtract one from the year diff to borrow a month and have enough            days to subtract Then from Now          if  dteNow Month    dteThen Month                        intDiffInYears   dteNow Year - dteThen Year - 1              intDiffInMonths   11     we borrowed a year and broke ONLY                 the LAST month into subtractable days                Stay with me -- because we borrowed days from the year  not the month                 this is much different than what appears to be a similar calculation below                 We know we re a full intDiffInYears years apart PLUS eleven months                 Now we need to know how many days occurred before dteThen was done with                 dteThen Month   Then we add the number of days we ve  earned  in the current                month                                  So 12 25 2009 to 12 1 2011 gives us                 11-9   2 years  minus one to borrow days   1 year difference                 1 year 11 months - 12 months   11 months difference                 days from 12 25 to the End Of Month     Begin of Month to 12 1                                    31-25                          0 1                                                  6                             1                                                                   7 days diff                               12 25 2009 to 12 1 2011 is 1 year  11 months  7 days apart   QED               int intDaysInSharedMonth   System DateTime DaysInMonth dteThen Year  dteThen Month               intDiffInDays   intDaysInSharedMonth - dteThen Day   dteNow Day                    else                       intDiffInYears   dteNow Year - dteThen Year              intDiffInMonths   dteNow Month - dteThen Month - 1                  So now figure out how many more days we d need to get from dteThen s                 intDiffInMonth-th month to get to the current month day in dteNow                 That is  if we re comparing 2 8 2011 to 11 7 2011  we ve got  10 8-2 8    8                full months between the two dates   But then we ve got to go from 10 8 to                11 07   So that s the previous month s  October  number of days  31  minus                the number of days into the month dteThen went  8   giving the number of days                needed to get us to the end of the month previous to dteNow  23    Now we                add back the number of days that we ve gone into dteNow s current month  7                 to get the total number of days we ve gone since we ran the greatest integer                function on the month difference  23 to the end of the month   7 into the                next month    30 total days   You gotta make it through October before you                 get another month  G  and it s got 31 days                int intDaysInPrevMonth   System DateTime DaysInMonth dteNow Year   dteNow Month - 1                intDiffInDays   intDaysInPrevMonth - dteThen Day   dteNow Day                    else          else dteThen Month  gt  dteNow Month  and we ve got to amend our year subtraction        because we haven t earned our entire year yet  and don t want an obo error      intDiffInYears   dteNow Year - dteThen Year - 1          So if the dates were THEN  6 15 1999 and NOW  2 20 2010           Diff in years is 2010-1999   11  but since we re not to 6 15 yet  it s only 10         Diff in months is  Months in year    12  -  Months lost between 1 1 1999 and 6 15 1999        when dteThen s clock wasn t yet rolling    6    6 months  then you add the months we        have made it into this year already   The clock s been rolling through 2 20  so two months         Note that if the 20 in 2 20 hadn t been bigger than the 15 in 6 15  we re back to the        intDaysInPrevMonth trick from earlier   We ll do that below  too      intDiffInMonths   12 - dteThen Month   dteNow Month       if  dteNow Day  gt   dteThen Day                intDiffInDays   dteNow Day - dteThen Day            else               intDiffInMonths--      subtract the month from which we re borrowing days              Maybe we shoulda factored this out previous to the if  dteNow Month  gt  dteThen Month             call  but I think this is more readable code          int intDaysInPrevMonth   System DateTime DaysInMonth dteNow Year   dteNow Month - 1            intDiffInDays   intDaysInPrevMonth - dteThen Day   dteNow Day            this addToBox  Years      intDiffInYears     Months      intDiffInMonths     Days      intDiffInDays      adds results to a rich text box

User · Answer

TimeSpan period   endDate AddDays 1  - startDate  DateTime date   new DateTime period Ticks   int totalYears   date Year - 1  int totalMonths     date Year - 1    12    date Month - 1  int totalWeeks    int period TotalDays   7    date Year - 1 because the year 0 doesn t exist  date Month - 1  the month 0 doesn t exist

User · Answer

int day 0 month 0 year 0  DateTime smallDate   Convert ToDateTime string Format   0     01 01 1900     DateTime bigDate   Convert ToDateTime string Format   0     05 06 2019     TimeSpan timeSpan   new TimeSpan       timeSpan is diff between bigDate and smallDate as days timeSpan   bigDate - smallDate     year is totalDays   365 as int year   timeSpan Days   365     smallDate AddYears year  is closing the difference for year because we found the year variable smallDate   smallDate AddYears year      again subtraction because we don t need the year now timeSpan   bigDate - smallDate     month is totalDays   30 as int month   timeSpan Days   30     smallDate AddMonths month  is closing the difference for month because we found the month variable smallDate   smallDate AddMonths month   if  bigDate  gt  smallDate        timeSpan   bigDate - smallDate      day   timeSpan Days      else it is mean already day is 0

User · Answer

DateTime dt1   new DateTime 2009  3  14   DateTime dt2   new DateTime 2008  3  15    int diffMonth   Math Abs  dt2 Year - dt1 Year  12   dt1 Month - dt2 Month

User · Answer

Console WriteLine  Enter your Date of Birth to Know your Current age in DD MM YY Format        string str   Console ReadLine        DateTime dt1   DateTime Parse str       DateTime dt2   DateTime Parse  10 06 2012        int result    dt2 - dt1  Days      result   result   365      Console WriteLine  Your Current age is  0  years   result

User · Answer

Days   endDate - startDate  Days Weeks   endDate - startDate  Days   7 Years  Months   12 Months  A TimeSpan only provides Days  so use the following code to get the number of whole months between a specified start and end date   For example  the number of whole months between 01 10 2000 and 02 10 2000 is 1   The the number of whole months between 01 10 2000 and 02 09 2000 is 0       public int getMonths DateTime startDate  DateTime endDate                int months   0           if  endDate Month  lt   startDate Month                        if  endDate Day  lt  startDate Day                                months    12    endDate Year - startDate Year - 1                             12 - startDate Month   endDate Month - 1                             else if  endDate Month  lt  startDate Month                                months    12    endDate Year - startDate Year - 1                             12 - startDate Month   endDate Month                             else      endDate Month    startDate Month   amp  amp   endDate Day  gt   startDate Day                                months    12    endDate Year - startDate Year                                    else if  endDate Day  lt  startDate Day                        months    12    endDate Year - startDate Year                         endDate Month - startDate Month  - 1                    else      endDate Month  gt  startDate Month   amp  amp   endDate Day  gt   startDate Day                        months    12    endDate Year - startDate Year                         endDate Month - startDate Month                      return months

User · Answer

I have below solution which works correctly for me After doing some Test cases   Extra Test cases are acceptable   public class DateDiffernce       private int m nDays   -1      private int m nWeek      private int m nMonth   -1      private int m nYear       public int Days               get                       return m nDays                       public int Weeks               get                       return m nWeek                       public int Months               get                       return m nMonth                       public int Years               get                       return m nYear                       public void GetDifferenceBetwwenTwoDate DateTime objDateTimeFromDate  DateTime objDateTimeToDate                if  objDateTimeFromDate Date  gt  objDateTimeToDate Date                        DateTime objDateTimeTemp   objDateTimeFromDate              objDateTimeFromDate   objDateTimeToDate              objDateTimeToDate   objDateTimeTemp                     if  objDateTimeFromDate    objDateTimeToDate                          textBoxDifferenceDays Text     Same dates                 textBoxAllDifference Text     Same dates               return                        If From Date s Day is bigger than borrow days from previous month             amp  then subtract          if  objDateTimeFromDate Day  gt  objDateTimeToDate Day                        objDateTimeToDate   objDateTimeToDate AddMonths -1               int nMonthDays   DateTime DaysInMonth objDateTimeToDate Year  objDateTimeToDate Month               m nDays   objDateTimeToDate Day   nMonthDays - objDateTimeFromDate Day                         If From Date s Month is bigger than borrow 12 Month              amp  then subtract          if  objDateTimeFromDate Month  gt  objDateTimeToDate Month                        objDateTimeToDate   objDateTimeToDate AddYears -1               m nMonth   objDateTimeToDate Month   12 - objDateTimeFromDate Month                       Below are best cases - simple subtraction         if  m nDays    -1                        m nDays   objDateTimeToDate Day - objDateTimeFromDate Day                     if  m nMonth    -1                        m nMonth   objDateTimeToDate Month - objDateTimeFromDate Month                     m nYear   objDateTimeToDate Year - objDateTimeFromDate Year          m nWeek   m nDays   7          m nDays   m nDays   7

User · Answer

Use the Subtract method of the DateTime object which returns a TimeSpan     DateTime dt1   new DateTime 2009  3  14   DateTime dt2   new DateTime 2008  3  15    TimeSpan ts   dt1 Subtract dt2    Double days   ts TotalDays  Double hours   ts TotalHours  Double years   ts TotalDays   365

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Leap years and uneven months actually make this a non-trivial problem  I m sure someone can come up with a more efficient way  but here s one option - approximate on the small side first and adjust up  untested    public static void GetDifference DateTime date1  DateTime date2  out int Years       out int Months  out int Weeks  out int Days          assumes date2 is the bigger date for simplicity        years     TimeSpan diff   date2 - date1      Years   diff Days   366      DateTime workingDate   date1 AddYears Years        while workingDate AddYears 1   lt   date2                workingDate   workingDate AddYears 1           Years                 months     diff   date2 - workingDate      Months   diff Days   31      workingDate   workingDate AddMonths Months        while workingDate AddMonths 1   lt   date2                workingDate   workingDate AddMonths 1           Months                 weeks and days     diff   date2 - workingDate      Weeks   diff Days   7    weeks always have 7 days     Days   diff Days   7

User · Answer

I was trying to find a clear answer for Years  Months and Days  and I didn t find anything clear  If you are still looking check this method           public static string GetDifference DateTime d1  DateTime d2                        int   monthDay   new int 12    31  -1  31  30  31  30  31  31  30  31  30  31                DateTime fromDate              DateTime toDate              int year              int month              int day               int increment   0               if  d1  gt  d2                                fromDate   d2                  toDate   d1                            else                               fromDate   d1                  toDate   d2                                 Calculating Days             if  fromDate Day  gt  toDate Day                                increment   monthDay fromDate Month - 1                              if  increment    -1                                if  DateTime IsLeapYear fromDate Year                                         increment   29                                    else                                       increment   28                                               if  increment    0                                day    toDate Day   increment  - fromDate Day                  increment   1                            else                               day   toDate Day - fromDate Day                                Month Calculation             if   fromDate Month   increment   gt  toDate Month                                month    toDate Month   12  -  fromDate Month   increment                   increment   1                            else                               month    toDate Month  -  fromDate Month   increment                   increment   0                                Year Calculation             year   toDate Year -  fromDate Year   increment                return year     years     month     months     day     days

User · Answer

Partly as a preparation for trying to answer this question correctly  and maybe even definitively      partly to examine how much one can trust code that is pasted on SO  and partly as an exercise in finding bugs  I created a bunch of unit tests for this question  and applied them to many proposed solutions from this page and a couple of duplicates   The results are conclusive  not a single one of the code contributions accurately answers the question  Update  I now have four correct solutions to this question  including my own  see updates below   Code tested  From this question  I tested code by the following users  Mohammed Ijas Nasirudeen  ruffin  Malu MN  Dave  pk   Jani  lc   These were all the answers which provided all three of years  months  and days in their code  Note that two of these  Dave and Jani  gave the total number of days and months  rather than the total number of months left after counting the years  and the total number of days left after counting the months  I think the answers are wrong in terms of what the OP seemed to want  but the unit tests obviously don t tell you much in these cases   Note that in Jani s case this was my error and his code was actually correct - see Update 4 below   The answers by Jon Skeet  Aghasoleimani  Mukesh Kumar  Richard  Colin  sheir  just i saw  Chalkey and Andy  were incomplete  This doesn t mean that the answers weren t any good  in fact several of them are useful contributions towards a solution  It just means that there wasn t code taking two DateTimes and returning 3 ints that I could properly test  Four of these do however talk about using TimeSpan  As many people have mentioned  TimeSpan doesn t return counts of anything larger than days   The other answers I tested were from    question 3054715 - LukeH  ho1 and this     curious geek question 6260372 - Chuck Rostance and Jani  same answer as this question  question 9     - Dylan Hayes  Jon and Rajeshwaran S P   this    curious geek s answer is code on a page he linked to  which I don t think he wrote  Jani s answer is the only one which uses an external library  Time Period Library for  Net   All other answers on all these questions seemed to be incomplete  Question 9 is about age in years  and the three answers are ones which exceeded the brief and calculated years  months and days  If anyone finds further duplicates of this question please let me know    How I tested  Quite simply  I made an interface  public interface IDateDifference     void SetDates DateTime start  DateTime end     int GetYears      int GetMonths      int GetDays         For each answer I wrote a class implementing this interface  using the copied and pasted code as a basis  Of course I had to adapt functions with different signatures etc  but I tried to make the minimal edits to do so  preserving all the logic code   I wrote a bunch of NUnit tests in an abstract generic class   TestFixture  public abstract class DateDifferenceTests lt DDC gt  where DDC   IDateDifference  new     and added an empty derived class   public class Rajeshwaran S P Test   DateDifferenceTests lt Rajeshwaran S P gt        to the source file for each IDateDifference class   NUnit is clever enough to do the rest   The tests  A couple of these were written in advance and the rest were written to try and break seemingly working implementations    TestFixture  public abstract class DateDifferenceTests lt DDC gt  where DDC   IDateDifference  new       protected IDateDifference ddClass      SetUp    public void Init           ddClass   new DDC            Test    public void BasicTest           ddClass SetDates new DateTime 2012  12  1   new DateTime 2012  12  25        CheckResults 0  0  24           Test    public void AlmostTwoYearsTest           ddClass SetDates new DateTime 2010  8  29   new DateTime 2012  8  14        CheckResults 1  11  16           Test    public void AlmostThreeYearsTest           ddClass SetDates new DateTime 2009  7  29   new DateTime 2012  7  14        CheckResults 2  11  15           Test    public void BornOnALeapYearTest           ddClass SetDates new DateTime 2008  2  29   new DateTime 2009  2  28        CheckControversialResults 0  11  30  1  0  0           Test    public void BornOnALeapYearTest2           ddClass SetDates new DateTime 2008  2  29   new DateTime 2009  3  1        CheckControversialResults 1  0  0  1  0  1            Test    public void LongMonthToLongMonth           ddClass SetDates new DateTime 2010  1  31   new DateTime 2010  3  31        CheckResults 0  2  0           Test    public void LongMonthToLongMonthPenultimateDay           ddClass SetDates new DateTime 2009  1  31   new DateTime 2009  3  30        CheckResults 0  1  30           Test    public void LongMonthToShortMonth           ddClass SetDates new DateTime 2009  8  31   new DateTime 2009  9  30        CheckControversialResults 0  1  0  0  0  30           Test    public void LongMonthToPartWayThruShortMonth           ddClass SetDates new DateTime 2009  8  31   new DateTime 2009  9  10        CheckResults 0  0  10          private void CheckResults int years  int months  int days          Assert AreEqual years  ddClass GetYears         Assert AreEqual months  ddClass GetMonths         Assert AreEqual days  ddClass GetDays            private void CheckControversialResults int years  int months  int days      int yearsAlt  int monthsAlt  int daysAlt             gives the right output but unhelpful messages     bool success     ddClass GetYears      years                       amp  amp  ddClass GetMonths      months                       amp  amp  ddClass GetDays      days                                              ddClass GetYears      yearsAlt                       amp  amp  ddClass GetMonths      monthsAlt                       amp  amp  ddClass GetDays      daysAlt         Assert IsTrue success           Most of the names are slightly silly and don t really explain why code might fail the test  however looking at the two dates and the answer s  should be enough to understand the test   There are two functions that do all the Asserts  CheckResults   and CheckControversialResults    These work well to save typing and give the right results  but unfortunately they make it harder to see exactly what went wrong  because the Assert in CheckControversialResults   will fail with  Expected true   rather than telling you which value was incorrect  If anyone has a better way to do this  avoid writing the same checks each time  but have more useful error messages  please let me know   CheckControversialResults   is used for a couple of cases where there seem to be two different opinions on what is right  I have an opinion of my own  but I thought I should be liberal in what I accepted here  The gist of this is deciding whether one year after Feb 29 is Feb 28 or Mar 1   These tests are the crux of the matter  and there could very well be errors in them  so please do comment if you find one which is wrong  It would be also good to hear some suggestions for other tests to check any future iterations of answers    No test involves time of day - all DateTimes are at midnight  Including times  as long as it s clear how rounding up and down to days works  I think it is   might show up even more flaws   The results  The complete scoreboard of results is as follows   ChuckRostance Test 3 failures               S S S F S S F S F Dave Test 6 failures                        F F S F F F F S S Dylan Hayes Test 9 failures                 F F F F F F F F F ho1 Test 3 failures                         F F S S S S F S S Jani Test 6 failures                        F F S F F F F S S Jon Test 1 failure                          S S S S S S F S S lc Test 2 failures                          S S S S S F F S S LukeH Test 1 failure                        S S S S S S F S S Malu MN Test 1 failure                      S S S S S S S F S Mohammed Ijas Nasirudeen Test 2 failures    F S S F S S S S S pk Test 6 failures                          F F F S S F F F S Rajeshwaran S P Test 7 failures             F F S F F S F F F ruffin Test 3 failures                      F S S F S S F S S this curious geek Test 2 failures           F S S F S S S S S   But note that Jani s solution was actually correct and passed all tests - see update 4 below   The columns are in alphabetical order of test name    AlmostThreeYearsTest AlmostTwoYearsTest BasicTest BornOnALeapYearTest BornOnALeapYearTest2 LongMonthToLongMonth LongMonthToLongMonthPenultimateDay LongMonthToPartWayThruShortMonth LongMonthToShortMonth   Three answers failed only 1 test each  Jon s  LukeH s and Manu MN s  Bear in mind these tests were probably written specifically to address flaws in those answers   Every test was passed by at least one piece of code  which is slightly reassuring that none of the tests are erroneous   Some answers failed a lot of tests  I hope no-one feels this is a condemnation of that poster s efforts  Firstly the number of successes is fairly arbitrary as the tests don t evenly cover the problem areas of the question space  Secondly this is not production code - answers are posted so people can learn from them  not copy them exactly into their programs  Code which fails a lot of tests can still have great ideas in it  At least one piece which failed a lot of tests had a small bug in it which I didn t fix  I m grateful to anyone who took the time to share their work with everyone else  for making this project so interesting   My conclusions  There are three    Calendars are hard  I wrote nine tests  including three where two answers are possible  Some of the tests where I only had one answer might not be unanimously agreed with  Just thinking about exactly what we mean when we say  1 month later  or  2 years earlier  is tricky in a lot of situations  And none of this code had to deal with all the complexities of things like working out when leap years are  All of it uses library code to handle dates  If you imagine the  spec  for telling time in days  weeks  months and years written out  there s all sorts of cruft  Because we know it pretty well since primary school  and use it everyday  we are blind to many of the idiosyncracies  The question is not an academic one - various types of decomposition of time periods into years  quarters and months are essential in accounting software for bonds and other financial products  Writing correct code is hard  There were a lot of bugs  In slightly more obscure topics or less popular questions than the chances of a bug existing without having been pointed out by a commenter are much  much higher than for this question  You should really never  never copy code from SO into your program without understanding exactly what it does  The flipside of this is that you probably shouldn t write code in your answer that is ready to be copied and pasted  but rather intelligent and expressive pseudo-code that allows someone to understand the solution and implement their own version  with their own bugs   Unit tests are helpful  I am still meaning to post my own solution to this when I get round to it  for someone else to find the hidden  incorrect assumptions in   Doing this was a great example of  saving the bugs  by turning them into unit tests to fix the next version of the code with    Update  The whole project is now at https   github com jwg4 date-difference This includes my own attempt jwg cs  which passes all the tests I currently have  including a few new ones which check for proper time of day handling  Feel free to add either more tests to break this and other implementations or better code for answering the question   Update 2   MattJohnson has added an implementation which uses Jon Skeet s NodaTime  It passes all the current tests   Update 3   KirkWoll s answer to Difference in months between two dates has been added to the project on github  It passes all the current tests   Update 4   Jani pointed out in a comment that I had used his code wrongly  He did suggest methods that counted the years  months and days correctly   alongside some which count the total number of days and months  not the remainders  however I mistakenly used the wrong ones in my test code  I have corrected my wrapper around his code and it now passes all tests  There are now four correct solutions  of which Jani s was the first  Two use libraries  Intenso TimePeriod and NodaTime  and two are written from scratch

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Subtract two DateTime instances to give you a TimeSpan which has a Days property   E g  in PowerShell     PS     datetime   today -  datetime  2009-04-07     Days                89 Hours               0 Minutes             0 Seconds             0 Milliseconds        0 Ticks               76896000000000 TotalDays           89 TotalHours          2136 TotalMinutes        128160 TotalSeconds        7689600 TotalMilliseconds   7689600000   Converting days into years or weeks is relatively easy  days in a year could be 365  365 25      depending on context   Months is much harder  because without a base date you don t know which month lengths apply   Assuming you want to start with your base date  you can incrementally substract while counting first years  checking for leap years   then month lengths  indexing from startDate Month   then weeks  remaining days divided by 7  and then days  remainder    There are a lot of edge cases to consider  e g  2005-03-01 is one year from 2004-03-01  and from 2004-02-29 depending on what you mean by  Year

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Based on Joaquim s answer  but fixing the calculation when end date month is less than start date month  and adding code to handle end date before start date           public static class GeneralHelper                     public static int GetYears DateTime startDate  DateTime endDate                                if  endDate  lt  startDate                      return -GetYears endDate  startDate                    int years    endDate Year - startDate Year                    if  endDate Year    startDate Year                      return years                   if  endDate Month  lt  startDate Month                      return years - 1                   if  endDate Month    startDate Month  amp  amp  endDate Day  lt  startDate Day                      return years - 1                   return years                             public static int GetMonths DateTime startDate  DateTime endDate                                if  startDate  gt  endDate                      return -GetMonths endDate  startDate                    int months   12   GetYears startDate  endDate                    if  endDate Month  gt  startDate Month                      months   months   endDate Month - startDate Month                  else                     months   12 - startDate Month   endDate Month                   if  endDate Day  lt  startDate Day                      months   months - 1                   return months                              TestClass        public class GeneralHelperTest                    TestMethod              public void GetYearsTest                                 Assert AreEqual 0  GeneralHelper GetYears new DateTime 2000  5  5   new DateTime 2000  12  31                     Assert AreEqual 0  GeneralHelper GetYears new DateTime 2000  5  5   new DateTime 2001  4  4                     Assert AreEqual 0  GeneralHelper GetYears new DateTime 2000  5  5   new DateTime 2001  5  4                     Assert AreEqual 1  GeneralHelper GetYears new DateTime 2000  5  5   new DateTime 2001  5  5                     Assert AreEqual 1  GeneralHelper GetYears new DateTime 2000  5  5   new DateTime 2001  12  31                      Assert AreEqual 0  GeneralHelper GetYears new DateTime 2000  12  31   new DateTime 2000  5  5                     Assert AreEqual 0  GeneralHelper GetYears new DateTime 2001  4  4   new DateTime 2000  5  5                     Assert AreEqual 0  GeneralHelper GetYears new DateTime 2001  5  4   new DateTime 2000  5  5                     Assert AreEqual -1  GeneralHelper GetYears new DateTime 2001  5  5   new DateTime 2000  5  5                     Assert AreEqual -1  GeneralHelper GetYears new DateTime 2001  12  31   new DateTime 2000  5  5                                 TestMethod              public void GetMonthsTest                                 Assert AreEqual 0  GeneralHelper GetMonths new DateTime 2000  5  5   new DateTime 2000  6  4                     Assert AreEqual 1  GeneralHelper GetMonths new DateTime 2000  5  5   new DateTime 2000  6  5                     Assert AreEqual 1  GeneralHelper GetMonths new DateTime 2000  5  5   new DateTime 2000  6  6                     Assert AreEqual 11  GeneralHelper GetMonths new DateTime 2000  5  5   new DateTime 2001  5  4                     Assert AreEqual 12  GeneralHelper GetMonths new DateTime 2000  5  5   new DateTime 2001  5  5                     Assert AreEqual 13  GeneralHelper GetMonths new DateTime 2000  5  5   new DateTime 2001  6  6                      Assert AreEqual 0  GeneralHelper GetMonths new DateTime 2000  6  4   new DateTime 2000  5  5                     Assert AreEqual -1  GeneralHelper GetMonths new DateTime 2000  6  5   new DateTime 2000  5  5                     Assert AreEqual -1  GeneralHelper GetMonths new DateTime 2000  6  6   new DateTime 2000  5  5                     Assert AreEqual -11  GeneralHelper GetMonths new DateTime 2001  5  4   new DateTime 2000  5  5                     Assert AreEqual -12  GeneralHelper GetMonths new DateTime 2001  5  5   new DateTime 2000  5  5                     Assert AreEqual -13  GeneralHelper GetMonths new DateTime 2001  6  6   new DateTime 2000  5  5                          EDIT No that still doesn t work  It fails this test   Assert AreEqual 24  GeneralHelper GetMonths new DateTime 2000  5  5   new DateTime 2003  5  5       Expected  lt 24   Actual  lt 12

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private void dateTimePicker1 ValueChanged object sender  EventArgs e             int gyear   dateTimePicker1 Value Year           int gmonth   dateTimePicker1 Value Month           int gday   dateTimePicker1 Value Day           int syear   DateTime Now Year           int smonth   DateTime Now Month           int sday   DateTime Now Day           int difday   DateTime DaysInMonth syear  gmonth            agedisplay    syear - gyear             lmonth    smonth - gmonth           lday    sday - gday             if  smonth  lt  gmonth                        agedisplay   agedisplay - 1                    if  smonth    gmonth                        if  sday  lt   gday                                 agedisplay   agedisplay - 1                                   if  smonth  lt  gmonth                        lmonth    - -smonth   -gmonth  12                     if  lday  lt  0                        lday   difday -  -lday               lmonth   lmonth - 1                     if  smonth    gmonth  amp  amp  sday  lt  gday amp  amp gyear  syear                        lmonth   11                         ageDisplay Text   Convert ToString agedisplay      Years       lmonth     Months       lday     Days

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If you subtract two instances of DateTime  that will return an instance of TimeSpan  which will represent the difference between the two dates

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This is actually quite tricky  A different total number of days can result in the same result  For example    19th June 2008 to 19th June 2010   2 years  but also 365   2 days 19th June 2006 to 19th June 2008   2 years  but also 365   366 days due to leap years   You may well want to subtract years until you get to the point where you ve got two dates which are less than a year apart  Then subtract months until you get to the point where you ve got two dates which are less than a month apart   Further confusion  subtracting  or adding  months is tricky when you might start with a date of  30th March  - what s a month earlier than that   Even further confusion  may not be relevant   even a day isn t always 24 hours  Daylight saving anyone   Even further confusion  almost certainly not relevant   even a minute isn t always 60 seconds  Leap seconds are highly confusing     I don t have the time to work out the exact right way of doing this right now - this answer is mostly to raise the fact that it s not nearly as simple as it might sound   EDIT  Unfortunately I m not going to have enough time to answer this fully  I would suggest you start off by defining a struct representing a Period   public struct Period       private readonly int days      public int Days   get   return days          private readonly int months      public int Months   get   return months          private readonly int years      public int Years   get   return years           public Period int years  int months  int days                this years   years          this months   months          this days   days             public Period WithDays int newDays                return new Period years  months  newDays              public Period WithMonths int newMonths                return new Period years  newMonths  days              public Period WithYears int newYears                return new Period newYears  months  days              public static DateTime operator   DateTime date  Period period                   TODO  Implement this             public static Period Difference DateTime first  DateTime second                   TODO  Implement this            I suggest you implement the   operator first  which should inform the Difference method - you should make sure that first    Period Difference first  second      second for all first second values   Start with writing a whole slew of unit tests - initially  easy  cases  then move on to tricky ones involving leap years  I know the normal approach is to write one test at a time  but I d personally brainstorm a bunch of them before you start any implementation work   Allow yourself a day to implement this properly  It s tricky stuff   Note that I ve omitted weeks here - that value at least is easy  because it s always 7 days  So given a  positive  period  you d have   int years   period Years  int months   period Months  int weeks   period Days   7  int daysWithinWeek   period Days   7     I suggest you avoid even thinking about negative periods - make sure everything is positive  all the time

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I came across this post while looking to solve a similar problem  I was trying to find the age of an animal in units of Years  Months  Weeks  and Days  Those values are then displayed in SpinEdits where the user can manually change the values to find estimate a birth date   When my form was passed a birth date from a month with less than 31 days  the value calculated was 1 day off  I based my solution off of Ic s answer above   Main calculation method that is called after my form loads           birthDateDisplay Text   birthDate ToString  MM dd yyyy             DateTime currentDate   DateTime Now           Int32 numOfDays   0           Int32 numOfWeeks   0          Int32 numOfMonths   0           Int32 numOfYears   0               changed code to follow this model http   stackoverflow com posts 1083990 revisions           years          TimeSpan diff   currentDate - birthDate          numOfYears   diff Days   366          DateTime workingDate   birthDate AddYears numOfYears            while  workingDate AddYears 1   lt   currentDate                        workingDate   workingDate AddYears 1               numOfYears                         months         diff   currentDate - workingDate          numOfMonths   diff Days   31          workingDate   workingDate AddMonths numOfMonths            while  workingDate AddMonths 1   lt   currentDate                        workingDate   workingDate AddMonths 1               numOfMonths                         weeks and days         diff   currentDate - workingDate          numOfWeeks   diff Days   7    weeks always have 7 days             if bday month is same as current month and bday day is after current day  the date is off by 1 day         if DateTime Now Month    birthDate Month  amp  amp  DateTime Now Day  lt  birthDate Day              numOfDays   diff Days   7   1          else             numOfDays   diff Days   7              If the there are fewer than 31 days in the birth month  the date calculated is 1 off            Dont need to add a day for the first day of the month         int daysInMonth   0          if   daysInMonth   DateTime DaysInMonth birthDate Year  birthDate Month      31  amp  amp  birthDate Day    1                        startDateforCalc   DateTime Now Date AddDays 31 - daysInMonth                  Need to add 1 more day if it is a leap year and Feb 29th is the date             if  DateTime IsLeapYear birthDate Year   amp  amp  birthDate Day    29                  startDateforCalc   startDateforCalc AddDays 1                      yearsSpinEdit Value   numOfYears          monthsSpinEdit Value   numOfMonths          weeksSpinEdit Value   numOfWeeks          daysSpinEdit Value   numOfDays    And then  in my spinEdit EditValueChanged event handler  I calculate the new birth date starting from my startDateforCalc based on the values in the spin edits   SpinEdits are constrained to only allow   0   birthDate   startDateforCalc Date AddYears -  Int32 yearsSpinEdit Value   AddMonths -  Int32 monthsSpinEdit Value   AddDays - 7     Int32 weeksSpinEdit Value      Int32 daysSpinEdit Value     birthDateDisplay Text   birthDate ToString  MM dd yyyy      I know its not the prettiest solution  but it seems to be working for me for all month lengths and years

[c#] How to get difference between two dates in Year/Month/Week/Day?

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