A very simple pair of extension methods on DateTime and DateTimeOffset to calculate the difference in months between two dates.

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 it can't be implemented as an extension method on TimeSpan because that doesn't retain knowledge of the actual dates used, and for months they're important.

Originally posted at StackOverflow.