Islamic concepts

ʿIddah عدة‎ — post-marital waiting period

2:234

For a widow, the post-marital period is 4 lunar months (of 29.53 days each) plus 10 days, which is equal to 4.21 months in the Western Gregorian calendar. (29.53*4+10)/(365.25/12) = 4.21

For a divorcee, the post-marital period is equal to 3 menstrual cycles, i.e. about 87 days.