months_since (ActiveSupport::CoreExtensions::Time::Calculations)

    # File lib/active_support/core_ext/time/calculations.rb, line 75
            def months_since(months)
              year, month, mday = self.year, self.month, self.mday

              month += months

              # in case months is negative
              while month < 1
                month += 12
                year -= 1
              end

              # in case months is positive
              while month > 12
                month -= 12
                year += 1
              end

              max = ::Time.days_in_month(month, year)
              mday = max if mday > max

              change(:year => year, :month => month, :mday => mday)
            end