§ 30. Month, computation. A number of months after or before a certain day shall be computed by counting such number of calendar months from such day, exclusive of 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 in days of the month as the day from which the computation is made, unless there be not so many days in the last month so counted, in which case the period computed shall expire with the last day of the month so counted.