N.D. Cent. Code § 1-02-15

The time in which any act provided by law is to be done is computed by excluding the first day and including the last, unless the last is a holiday, and then it also is excluded. If a number of months is to be computed by counting the months from a particular day, the period ends on the same numerical day in the concluding month as the day of the month from which the computation is begun, unless there are not that many days in the concluding month, in which case the period ends on the last day of that month.