How is the waiting period (iddah) calculated in Hijri months?

If you are pregnant, your 'iddah (definition) (waiting period) ends upon giving birth to the entire pregnancy, as Allah Almighty says: "And for those who are pregnant, their term is that they deliver their pregnancy." (Quran 65:4) If you are not pregnant, your 'iddah is four months and ten days, as Allah Almighty says: "And those of you who die and leave wives behind - they, [the wives], shall wait four months and ten [days]." (Quran 2:234)

If the husband's death occurred on the 14th of Jumada al-Akhirah (definition), 1435 AH, then the 'iddah begins immediately from that date and ends on the 24th of Shawwal, 1435 AH, at the exact time the death occurred, if Jumada al-Akhirah was thirty days. However, if it was twenty-nine days, then the 'iddah extends to the 25th of Shawwal. The remaining months are calculated by the sighting of the crescent moon, whether they are thirty or twenty-nine days.