The Talmud teaches that evildoers are sentenced to gehinnom for twelve months. Accordingly, as the Rama (Yoreh Deah 376:4) points out, one recites kaddish for a parent for eleven months, so as not to create the impression that the parent is presumed to be evil. This ruling thus creates a question as to whether an adjustment should be made for a leap year, which is thirteen months long. R. Natan Gestetner (Resp. L’Horot Natan, I, 52) observes that since the statement speaks in terms of months, twelves months is taken to mean exactly that, and not a way of indicating “a year”. This is reflected in the ruling of the Shulchan Arukh (C.M. 312:15) that if one rents a house for a year, and that year becomes a leap year, the renter gains an extra month; but if the lease is expressed in terms of months, the renter does not gain any time from the leap year. Thus, no adjustment in Kaddish would be made.

R. Gestetner notes that a question can be raised against this ruling based on the fact that the Mishnah (Eduyot 2:10) that records the sentence of evildoers cites the verse (Yeshayahu 66:23) “And it shall come to pass, that from one new moon to another”. As noted by the Ra’avad and the Tos. Santz, this suggests that the punishment begins on one date of a month and concludes on that same date of the same month the next time around. Thus, it would appear that the reference is to an actual year, and therefore thirteen months in a leap year. However, R. Gestetner dismisses this question, finding it improbable that the creation of a leap year on Earth would necessitate a longer period of punishment for those who have already left the Earth.