Whenever in any rule the lapse of a number of months after or before a certain day is required, such number of months shall be computed by counting the months from such day, excluding the calendar month in which such day occurs, and shall include the day of the month in the last month so counted having the same numerical order as the day of the month from which the computation is made, unless there are not so many days in the last month so counted, in which case the period computed shall expire with the last day of such month.