Difference in months between two dates

Question

How to calculate the difference in months between two dates in C#?

Is there is equivalent of VB's DateDiff() method in C#. I need to find difference in months between two dates that are years apart. The documentation says that I can use TimeSpan like:

TimeSpan ts = date1 - date2; 

but this gives me data in Days. I don't want to divide this number by 30 because not every month is 30 days and since the two operand values are quite apart from each other, I am afraid dividing by 30 might give me a wrong value.

Any suggestions?

Answer 1

Assuming the day of the month is irrelevant (i.e. the diff between 2011.1.1 and 2010.12.31 is 1), with date1 > date2 giving a positive value and date2 > date1 a negative value

((date1.Year - date2.Year) * 12) + date1.Month - date2.Month 

Or, assuming you want an approximate number of 'average months' between the two dates, the following should work for all but very huge date differences.

date1.Subtract(date2).Days / (365.25 / 12) 

Note, if you were to use the latter solution then your unit tests should state the widest date range which your application is designed to work with and validate the results of the calculation accordingly.

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Update (with thanks to Gary)

If using the 'average months' method, a slightly more accurate number to use for the 'average number of days per year' is 365.2425.