Difference in months between two dates

Here is a comprehensive solution to return a DateTimeSpan, similar to a TimeSpan, except that it includes all the date components in addition to the time components.

Usage:

void Main() { DateTime compareTo = DateTime.Parse("8/13/2010 8:33:21 AM"); DateTime now = DateTime.Parse("2/9/2012 10:10:11 AM"); var dateSpan = DateTimeSpan.CompareDates(compareTo, now); Console.WriteLine("Years: " + dateSpan.Years); Console.WriteLine("Months: " + dateSpan.Months); Console.WriteLine("Days: " + dateSpan.Days); Console.WriteLine("Hours: " + dateSpan.Hours); Console.WriteLine("Minutes: " + dateSpan.Minutes); Console.WriteLine("Seconds: " + dateSpan.Seconds); Console.WriteLine("Milliseconds: " + dateSpan.Milliseconds); } 

Outputs:

Years: 1
Months: 5
Days: 27
Hours: 1
Minutes: 36
Seconds: 50
Milliseconds: 0

For convenience, I've lumped the logic into the DateTimeSpan struct, but you may move the method CompareDates wherever you see fit. Also note, it doesn't matter which date comes before the other.

public struct DateTimeSpan { public int Years { get; } public int Months { get; } public int Days { get; } public int Hours { get; } public int Minutes { get; } public int Seconds { get; } public int Milliseconds { get; } public DateTimeSpan(int years, int months, int days, int hours, int minutes, int seconds, int milliseconds) { Years = years; Months = months; Days = days; Hours = hours; Minutes = minutes; Seconds = seconds; Milliseconds = milliseconds; } enum Phase { Years, Months, Days, Done } public static DateTimeSpan CompareDates(DateTime date1, DateTime date2) { if (date2 < date1) { var sub = date1; date1 = date2; date2 = sub; } DateTime current = date1; int years = 0; int months = 0; int days = 0; Phase phase = Phase.Years; DateTimeSpan span = new DateTimeSpan(); int officialDay = current.Day; while (phase != Phase.Done) { switch (phase) { case Phase.Years: if (current.AddYears(years + 1) > date2) { phase = Phase.Months; current = current.AddYears(years); } else { years++; } break; case Phase.Months: if (current.AddMonths(months + 1) > date2) { phase = Phase.Days; current = current.AddMonths(months); if (current.Day < officialDay && officialDay <= DateTime.DaysInMonth(current.Year, current.Month)) current = current.AddDays(officialDay - current.Day); } else { months++; } break; case Phase.Days: if (current.AddDays(days + 1) > date2) { current = current.AddDays(days); var timespan = date2 - current; span = new DateTimeSpan(years, months, days, timespan.Hours, timespan.Minutes, timespan.Seconds, timespan.Milliseconds); phase = Phase.Done; } else { days++; } break; } } return span; } } 

You could do

if ( date1.AddMonths(x) > date2 ) 

If you want the exact number of full months, always positive (2000-01-15, 2000-02-14 returns 0), considering a full month is when you reach the same day the next month (something like the age calculation)

public static int GetMonthsBetween(DateTime from, DateTime to) { if (from > to) return GetMonthsBetween(to, from); var monthDiff = Math.Abs((to.Year * 12 + (to.Month - 1)) - (from.Year * 12 + (from.Month - 1))); if (from.AddMonths(monthDiff) > to || to.Day < from.Day) { return monthDiff - 1; } else { return monthDiff; } } 

Edit reason: the old code was not correct in some cases like :

new { From = new DateTime(1900, 8, 31), To = new DateTime(1901, 8, 30), Result = 11 }, Test cases I used to test the function: var tests = new[] { new { From = new DateTime(1900, 1, 1), To = new DateTime(1900, 1, 1), Result = 0 }, new { From = new DateTime(1900, 1, 1), To = new DateTime(1900, 1, 2), Result = 0 }, new { From = new DateTime(1900, 1, 2), To = new DateTime(1900, 1, 1), Result = 0 }, new { From = new DateTime(1900, 1, 1), To = new DateTime(1900, 2, 1), Result = 1 }, new { From = new DateTime(1900, 2, 1), To = new DateTime(1900, 1, 1), Result = 1 }, new { From = new DateTime(1900, 1, 31), To = new DateTime(1900, 2, 1), Result = 0 }, new { From = new DateTime(1900, 8, 31), To = new DateTime(1900, 9, 30), Result = 0 }, new { From = new DateTime(1900, 8, 31), To = new DateTime(1900, 10, 1), Result = 1 }, new { From = new DateTime(1900, 1, 1), To = new DateTime(1901, 1, 1), Result = 12 }, new { From = new DateTime(1900, 1, 1), To = new DateTime(1911, 1, 1), Result = 132 }, new { From = new DateTime(1900, 8, 31), To = new DateTime(1901, 8, 30), Result = 11 }, }; 

I checked the usage of this method in VB.NET via MSDN and it seems that it has a lot of usages. There is no such a built-in method in C#. (Even it's not a good idea) you can call VB's in C#.

1. Add Microsoft.VisualBasic.dll to your project as a reference
2. use Microsoft.VisualBasic.DateAndTime.DateDiff in your code

To get difference in months (both start and end inclusive), irrespective of dates:

DateTime start = new DateTime(2013, 1, 1); DateTime end = new DateTime(2014, 2, 1); var diffMonths = (end.Month + end.Year * 12) - (start.Month + start.Year * 12); 

Use Noda Time:

LocalDate start = new LocalDate(2013, 1, 5); LocalDate end = new LocalDate(2014, 6, 1); Period period = Period.Between(start, end, PeriodUnits.Months); Console.WriteLine(period.Months); // 16 

(example source)

I just needed something simple to cater for e.g. employment dates where only the month/year is entered, so wanted distinct years and months worked in. This is what I use, here for usefullness only

public static YearsMonths YearMonthDiff(DateTime startDate, DateTime endDate) { int monthDiff = ((endDate.Year * 12) + endDate.Month) - ((startDate.Year * 12) + startDate.Month) + 1; int years = (int)Math.Floor((decimal) (monthDiff / 12)); int months = monthDiff % 12; return new YearsMonths { TotalMonths = monthDiff, Years = years, Months = months }; } 

.NET Fiddle

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 < 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.

You can use the DateDiff class of the Time Period Library for .NET:

// ---------------------------------------------------------------------- public void DateDiffSample() { DateTime date1 = new DateTime( 2009, 11, 8, 7, 13, 59 ); DateTime date2 = new DateTime( 2011, 3, 20, 19, 55, 28 ); DateDiff dateDiff = new DateDiff( date1, date2 ); // differences Console.WriteLine( "DateDiff.Months: {0}", dateDiff.Months ); // > DateDiff.Months: 16 // elapsed Console.WriteLine( "DateDiff.ElapsedMonths: {0}", dateDiff.ElapsedMonths ); // > DateDiff.ElapsedMonths: 4 // description 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 

You can use Noda Time https://nodatime.org/

LocalDate start = new LocalDate(2010, 1, 5); LocalDate end = new LocalDate(2012, 6, 1); Period period = Period.Between(start, end, PeriodUnits.Months); Console.WriteLine(period.Months); 

My understanding of the total months difference between 2 dates has an integral and a fractional part (the date matters).

The integral part is the full months difference.

The fractional part, for me, is the difference of the % of the day (to the full days of month) between the starting and ending months.

public static class DateTimeExtensions { public static double TotalMonthsDifference(this DateTime from, DateTime to) { //Compute full months difference between dates var fullMonthsDiff = (to.Year - from.Year)*12 + to.Month - from.Month; //Compute difference between the % of day to full days of each month var fractionMonthsDiff = ((double)(to.Day-1) / (DateTime.DaysInMonth(to.Year, to.Month)-1)) - ((double)(from.Day-1)/ (DateTime.DaysInMonth(from.Year, from.Month)-1)); return fullMonthsDiff + fractionMonthsDiff; } } 

With this extension, those are the results:

2/29/2000 TotalMonthsDifference 2/28/2001 => 12 2/28/2000 TotalMonthsDifference 2/28/2001 => 12.035714285714286 01/01/2000 TotalMonthsDifference 01/16/2000 => 0.5 01/31/2000 TotalMonthsDifference 01/01/2000 => -1.0 01/31/2000 TotalMonthsDifference 02/29/2000 => 1.0 01/31/2000 TotalMonthsDifference 02/28/2000 => 0.9642857142857143 01/31/2001 TotalMonthsDifference 02/28/2001 => 1.0 

one line solution

For first, check if both dates are in the current year, if not get months of whole years and then add months from the start and end year.

DateTime dateFrom = new DateTime(2019, 2, 1); DateTime dateTo = new DateTime(2021, 5, 25); 

With the first month

var monthCount = dateFrom.Year != dateTo.Year ? ((dateTo.Year - dateFrom.Year - 1) * 12) + (13 - dateFrom.Month + dateTo.Month) : dateTo.Month - dateFrom.Month + 1; 

result = 28

Without first month

monthCount = dateFrom.Year != dateTo.Year ? ((dateTo.Year - dateFrom.Year - 1) * 12) + (12 - dateFrom.Month + dateTo.Month) : dateTo.Month - dateFrom.Month; 

result = 27

This worked for what I needed it for. The day of month didn't matter in my case because it always happens to be the last day of the month.

public static int MonthDiff(DateTime d1, DateTime d2){ int retVal = 0; if (d1.Month<d2.Month) { retVal = (d1.Month + 12) - d2.Month; retVal += ((d1.Year - 1) - d2.Year)*12; } else { retVal = d1.Month - d2.Month; retVal += (d1.Year - d2.Year)*12; } //// Calculate the number of years represented and multiply by 12 //// Substract the month number from the total //// Substract the difference of the second month and 12 from the total //retVal = (d1.Year - d2.Year) * 12; //retVal = retVal - d1.Month; //retVal = retVal - (12 - d2.Month); return retVal; } 

There's 3 cases: same year, previous year and other years.

If the day of the month does not matter...

public int GetTotalNumberOfMonths(DateTime start, DateTime end) { // work with dates in the right order if (start > end) { var swapper = start; start = end; end = swapper; } switch (end.Year - start.Year) { case 0: // Same year return end.Month - start.Month; case 1: // last year return (12 - start.Month) + end.Month; default: return 12 * (3 - (end.Year - start.Year)) + (12 - start.Month) + end.Month; } } 

The most precise way is this that return difference in months by fraction :

private double ReturnDiffereceBetweenTwoDatesInMonths(DateTime startDateTime, DateTime endDateTime) { double result = 0; double days = 0; DateTime currentDateTime = startDateTime; while (endDateTime > currentDateTime.AddMonths(1)) { result ++; currentDateTime = currentDateTime.AddMonths(1); } if (endDateTime > currentDateTime) { days = endDateTime.Subtract(currentDateTime).TotalDays; } return result + days/endDateTime.GetMonthDays; } 

Here is a simple solution that works at least for me. It's probably not the fastest though because it uses the cool DateTime's AddMonth feature in a loop:

public static int GetMonthsDiff(DateTime start, DateTime end) { if (start > end) return GetMonthsDiff(end, start); int months = 0; do { start = start.AddMonths(1); if (start > end) return months; months++; } while (true); } 

This simple static function calculates the fraction of months between two Datetimes, e.g.

• 1.1. to 31.1. = 1.0
• 1.4. to 15.4. = 0.5
• 16.4. to 30.4. = 0.5
• 1.3. to 1.4. = 1 + 1/30

The function assumes that the first date is smaller than the second date. To deal with negative time intervals one can modify the function easily by introducing a sign and a variable swap at the beginning.

public static double GetDeltaMonths(DateTime t0, DateTime t1) { DateTime t = t0; double months = 0; while(t<=t1) { int daysInMonth = DateTime.DaysInMonth(t.Year, t.Month); DateTime endOfMonth = new DateTime(t.Year, t.Month, daysInMonth); int cutDay = endOfMonth <= t1 ? daysInMonth : t1.Day; months += (cutDay - t.Day + 1) / (double) daysInMonth; t = new DateTime(t.Year, t.Month, 1).AddMonths(1); } return Math.Round(months,2); } 

I was working on a project that only dealt in years and months.

/// <summary> /// Get the total months between two date. This will count whole months and not care about the day. /// </summary> /// <param name="firstDate">First date.</param> /// <param name="lastDate">Last date.</param> /// <returns>Number of month apart.</returns> private static int GetTotalMonths(DateOnly firstDate, DateOnly lastDate) { int yearsApart = lastDate.Year - firstDate.Year; int monthsApart = lastDate.Month - firstDate.Month; return (yearsApart * 12) + monthsApart; } private static int GetTotalMonths(DateTime firstDate, DateTime lastDate) { return GetTotalMonths(DateOnly.FromDateTime(firstDate), DateOnly.FromDateTime(lastDate)); } 

Someone must have done it))

The extension method returns the number of full months between the given dates. No matter in what order the dates are received, a natural number will always be returned.No approximate calculations as in the "correct" answer.

 /// <summary> /// Returns the difference between dates in months. /// </summary> /// <param name="current">First considered date.</param> /// <param name="another">Second considered date.</param> /// <returns>The number of full months between the given dates.</returns> public static int DifferenceInMonths(this DateTime current, DateTime another) { DateTime previous, next; if (current > another) { previous = another; next = current; } else { previous = current; next = another; } return (next.Year - previous.Year) * 12 // multiply the difference in years by 12 months + next.Month - previous.Month // add difference in months + (previous.Day <= next.Day ? 0 : -1); // if the day of the next date has not reached the day of the previous one, then the last month has not yet ended } 

But if you still want to get the fractional parts of the months, you just need to add one more term to the return:

+ (next.Day - previous.Day) / DateTime.DaysInMonth(previous.Year, previous.Month)

Um, actually, the OP asked for something like VB's DateDiff(). It turns out that that function works very simply for months:

((LastDate.Year - FirstDate.Year) * 12) + LastDate.Month - FirstDate.Month 

seems to emulate it perfectly.

(Unless I be mistaken. I'll welcome anyone pointing out a mistake.)

Public Class ClassDateOperation Private prop_DifferenceInDay As Integer Private prop_DifferenceInMonth As Integer Private prop_DifferenceInYear As Integer Public Function DayMonthYearFromTwoDate(ByVal DateStart As Date, ByVal DateEnd As Date) As ClassDateOperation Dim differenceInDay As Integer Dim differenceInMonth As Integer Dim differenceInYear As Integer Dim myDate As Date DateEnd = DateEnd.AddDays(1) differenceInYear = DateEnd.Year - DateStart.Year If DateStart.Month <= DateEnd.Month Then differenceInMonth = DateEnd.Month - DateStart.Month Else differenceInYear -= 1 differenceInMonth = (12 - DateStart.Month) + DateEnd.Month End If If DateStart.Day <= DateEnd.Day Then differenceInDay = DateEnd.Day - DateStart.Day Else myDate = CDate("01/" & DateStart.AddMonths(1).Month & "/" & DateStart.Year).AddDays(-1) If differenceInMonth <> 0 Then differenceInMonth -= 1 Else differenceInMonth = 11 differenceInYear -= 1 End If differenceInDay = myDate.Day - DateStart.Day + DateEnd.Day End If prop_DifferenceInDay = differenceInDay prop_DifferenceInMonth = differenceInMonth prop_DifferenceInYear = differenceInYear Return Me End Function Public ReadOnly Property DifferenceInDay() As Integer Get Return prop_DifferenceInDay End Get End Property Public ReadOnly Property DifferenceInMonth As Integer Get Return prop_DifferenceInMonth End Get End Property Public ReadOnly Property DifferenceInYear As Integer Get Return prop_DifferenceInYear End Get End Property End Class 

This is from my own library, will return the difference of months between two dates.

public static int MonthDiff(DateTime d1, DateTime d2) { int retVal = 0; // Calculate the number of years represented and multiply by 12 // Substract the month number from the total // Substract the difference of the second month and 12 from the total retVal = (d1.Year - d2.Year) * 12; retVal = retVal - d1.Month; retVal = retVal - (12 - d2.Month); return retVal; } 

You can have a function something like this.

For Example, from 2012/12/27 to 2012/12/29 becomes 3 days. Likewise, from 2012/12/15 to 2013/01/15 becomes 2 months, because up to 2013/01/14 it's 1 month. from 15th it's 2nd month started.

You can remove the "=" in the second if condition, if you do not want to include both days in the calculation. i.e, from 2012/12/15 to 2013/01/15 is 1 month.

public int GetMonths(DateTime startDate, DateTime endDate) { if (startDate > endDate) { throw new Exception("Start Date is greater than the End Date"); } int months = ((endDate.Year * 12) + endDate.Month) - ((startDate.Year * 12) + startDate.Month); if (endDate.Day >= startDate.Day) { months++; } return months; } 

you can use the following extension: Code

public static class Ext { #region Public Methods public static int GetAge(this DateTime @this) { var today = DateTime.Today; return ((((today.Year - @this.Year) * 100) + (today.Month - @this.Month)) * 100 + today.Day - @this.Day) / 10000; } public static int DiffMonths(this DateTime @from, DateTime @to) { return (((((@to.Year - @from.Year) * 12) + (@to.Month - @from.Month)) * 100 + @to.Day - @from.Day) / 100); } public static int DiffYears(this DateTime @from, DateTime @to) { return ((((@to.Year - @from.Year) * 100) + (@to.Month - @from.Month)) * 100 + @to.Day - @from.Day) / 10000; } #endregion Public Methods } 

Implementation !

int Age; int years; int Months; //Replace your own date var d1 = new DateTime(2000, 10, 22); var d2 = new DateTime(2003, 10, 20); //Age Age = d1.GetAge(); Age = d2.GetAge(); //positive years = d1.DiffYears(d2); Months = d1.DiffMonths(d2); //negative years = d2.DiffYears(d1); Months = d2.DiffMonths(d1); //Or Months = Ext.DiffMonths(d1, d2); years = Ext.DiffYears(d1, d2); 

Here's a much more concise solution using VB.Net DateDiff for Year, Month, Day only. You can load the DateDiff library in C# as well.

date1 must be <= date2

VB.NET

Dim date1 = Now.AddDays(-2000) Dim date2 = Now Dim diffYears = DateDiff(DateInterval.Year, date1, date2) - If(date1.DayOfYear > date2.DayOfYear, 1, 0) Dim diffMonths = DateDiff(DateInterval.Month, date1, date2) - diffYears * 12 - If(date1.Day > date2.Day, 1, 0) Dim diffDays = If(date2.Day >= date1.Day, date2.Day - date1.Day, date2.Day + (Date.DaysInMonth(date1.Year, date1.Month) - date1.Day)) 

C#

DateTime date1 = Now.AddDays(-2000); DateTime date2 = Now; int diffYears = DateDiff(DateInterval.Year, date1, date2) - date1.DayOfYear > date2.DayOfYear ? 1 : 0; int diffMonths = DateDiff(DateInterval.Month, date1, date2) - diffYears * 12 - date1.Day > date2.Day ? 1 : 0; int diffDays = date2.Day >= date1.Day ? date2.Day - date1.Day : date2.Day + (System.DateTime.DaysInMonth(date1.Year, date1.Month) - date1.Day); 

This is in response to Kirk Woll's answer. I don't have enough reputation points to reply to a comment yet...

I liked Kirk's solution and was going to shamelessly rip it off and use it in my code, but when I looked through it I realized it's way too complicated. Unnecessary switching and looping, and a public constructor that is pointless to use.

Here's my rewrite:

public class DateTimeSpan { private DateTime _date1; private DateTime _date2; private int _years; private int _months; private int _days; private int _hours; private int _minutes; private int _seconds; private int _milliseconds; public int Years { get { return _years; } } public int Months { get { return _months; } } public int Days { get { return _days; } } public int Hours { get { return _hours; } } public int Minutes { get { return _minutes; } } public int Seconds { get { return _seconds; } } public int Milliseconds { get { return _milliseconds; } } public DateTimeSpan(DateTime date1, DateTime date2) { _date1 = (date1 > date2) ? date1 : date2; _date2 = (date2 < date1) ? date2 : date1; _years = _date1.Year - _date2.Year; _months = (_years * 12) + _date1.Month - _date2.Month; TimeSpan t = (_date2 - _date1); _days = t.Days; _hours = t.Hours; _minutes = t.Minutes; _seconds = t.Seconds; _milliseconds = t.Milliseconds; } public static DateTimeSpan CompareDates(DateTime date1, DateTime date2) { return new DateTimeSpan(date1, date2); } } 

Usage1, pretty much the same:

void Main() { DateTime compareTo = DateTime.Parse("8/13/2010 8:33:21 AM"); DateTime now = DateTime.Parse("2/9/2012 10:10:11 AM"); var dateSpan = new DateTimeSpan(compareTo, now); Console.WriteLine("Years: " + dateSpan.Years); Console.WriteLine("Months: " + dateSpan.Months); Console.WriteLine("Days: " + dateSpan.Days); Console.WriteLine("Hours: " + dateSpan.Hours); Console.WriteLine("Minutes: " + dateSpan.Minutes); Console.WriteLine("Seconds: " + dateSpan.Seconds); Console.WriteLine("Milliseconds: " + dateSpan.Milliseconds); } 

Usage2, similar:

void Main() { DateTime compareTo = DateTime.Parse("8/13/2010 8:33:21 AM"); DateTime now = DateTime.Parse("2/9/2012 10:10:11 AM"); Console.WriteLine("Years: " + DateTimeSpan.CompareDates(compareTo, now).Years); Console.WriteLine("Months: " + DateTimeSpan.CompareDates(compareTo, now).Months); Console.WriteLine("Days: " + DateTimeSpan.CompareDates(compareTo, now).Days); Console.WriteLine("Hours: " + DateTimeSpan.CompareDates(compareTo, now).Hours); Console.WriteLine("Minutes: " + DateTimeSpan.CompareDates(compareTo, now).Minutes); Console.WriteLine("Seconds: " + DateTimeSpan.CompareDates(compareTo, now).Seconds); Console.WriteLine("Milliseconds: " + DateTimeSpan.CompareDates(compareTo, now).Milliseconds); } 

In my case it is required to calculate the complete month from the start date to the day prior to this day in the next month or from start to end of month.

Ex: from 1/1/2018 to 31/1/2018 is a complete month
Ex2: from 5/1/2018 to 4/2/2018 is a complete month

so based on this here is my solution:

public static DateTime GetMonthEnd(DateTime StartDate, int MonthsCount = 1) { return StartDate.AddMonths(MonthsCount).AddDays(-1); } public static Tuple<int, int> CalcPeriod(DateTime StartDate, DateTime EndDate) { int MonthsCount = 0; Tuple<int, int> Period; while (true) { if (GetMonthEnd(StartDate) > EndDate) break; else { MonthsCount += 1; StartDate = StartDate.AddMonths(1); } } int RemainingDays = (EndDate - StartDate).Days + 1; Period = new Tuple<int, int>(MonthsCount, RemainingDays); return Period; } 

Usage:

Tuple<int, int> Period = CalcPeriod(FromDate, ToDate); 

Note: in my case it was required to calculate the remaining days after the complete months so if it's not your case you could ignore the days result or even you could change the method return from tuple to integer.

public static int PayableMonthsInDuration(DateTime StartDate, DateTime EndDate) { int sy = StartDate.Year; int sm = StartDate.Month; int count = 0; do { count++;if ((sy == EndDate.Year) && (sm >= EndDate.Month)) { break; } sm++;if (sm == 13) { sm = 1; sy++; } } while ((EndDate.Year >= sy) || (EndDate.Month >= sm)); return (count); } 

This solution is for Rental/subscription calculation, where difference doesn't means to be subtraction, it's meant to be the span in within those two dates.

I wrote a function to accomplish this, because the others ways weren't working for me.

public string getEndDate (DateTime startDate,decimal monthCount) { int y = startDate.Year; int m = startDate.Month; for (decimal i = monthCount; i > 1; i--) { m++; if (m == 12) { y++; m = 1; } } return string.Format("{0}-{1}-{2}", y.ToString(), m.ToString(), startDate.Day.ToString()); }