Some simple TimeSpan extension methods that add approximations for total weeks, months and years in a timespan.

TimeSpanExtensions.cs

using System;

public static class TimeSpanExtensions
{
	const double DaysInWeek = 7d;
	const double DaysInMonth = 365d / 12d;
	const double DaysInYear = 365d;

	public static double TotalWeeks(this TimeSpan val)
	{
		return val.TotalDays / DaysInWeek;
	}

	public static double TotalMonths(this TimeSpan val)
	{
		return val.TotalDays / DaysInMonth;
	}

	public static double TotalYears(this TimeSpan val)
	{
		return val.TotalDays / DaysInYear;
	}
}