How is the year calculated when stipulated in a divorce oath, such as saying 'If a year passes, you are divorced'?
Chapter on Explicit Divorce and Others
Al-Mughni
Book of Divorce
Primary text
When a year is stipulated in an oath, the year begins from the moment of the oath and completes twelve lunar months (Ahillah). This is based on the verse: Quran 2:189. If the oath is sworn at the beginning of a month, the divorce occurs when twelve full months have passed. If the oath is sworn in the middle of a month, the remaining days of that first month are counted, and the subsequent eleven months are counted by the lunar cycle. After eleven full lunar months have passed, the remainder of the first month is completed by considering it thirty days, as a month is defined as the period between two new moons.
Supporting text
There is an alternative view, affirmed by Ahmad, that all months should be calculated purely by count (number of days). This is evidenced when someone vows to fast two consecutive months; if they fast fifty-eight days spanning two calendar months, it suffices, implying that the remainder of the first partial month is completed from the second month, requiring completion by count.