There is a widespread custom to observe a fast on a Yartzeit, the anniversary of the passing of an immediately family member, Heaven forbid, particularly on the Yartzeit of one's parent. Maran (author of the Shulhan Aruch) documents this custom in Bedek Ha'bayit (Y.D. 344) as well as in Shulhan Aruch (O.H. 598:8). The Rema (Rabbi Moshe Isserles, Poland, 1525-1572) similarly records this practice in his glosses to the Shulhan Aruch (Y.D. 402), adding that it is proper also to perform special Misvot such as giving charity as part of the Yartzeit observance.
The question arises, if the burial was, for whatever reason, delayed, and did not occur on the day of the person's passing, when is the Yartzeit observed? For example, if somebody passed away, Heaven forbid, on the fifth of the month, and his remains were flown to Eretz Yisrael and buried on the sixth, do we determine the Yartzeit based on the date of his passing the fifth of that month or the date of his burial the sixth of that month?
While all authorities agree that the Yartzeit is determined based on the day of the passing, they debate the question of whether this applies even on the first year after the individual's death. The Ben Ish Hai (Rabbi Yosef Haim of Baghdad, 1833-1909), in his work Rav Pe'alim (vol. 1, Y.D. 51), maintains that in the first year after the family member's passing, the Yartzeit is observed on the date of the burial, rather than on the date of the passing. This is the view of Hacham Bension Abba Shaul (Jerusalem, 1923-1998), as well. Hacham Ovadia Yosef, however, in his work Yabia Omer (vol. 5, Y.D. 32), cites numerous earlier authorities (including the Ma'aseh Avraham, Sha'agat Aryeh, Melamed Le'ho'il, Kenesset Yehezkel and Maharsham) who rule that even in the first year, the Yartzeit is commemorated on the date of the passing. Accordingly, he rules against the position of the Ben Ish Hai and Hacham Bension Abba Shaul, and claims that the Yartzeit is always commemorated on the date on which the family member passed away.
Given the different traditions that exist in this regard, should this situation ever arise, Heaven forbid, one should consult with his Rabbi for guidance.
Summary: There is a custom to fast and perform special Misvot on the anniversary of a family member's passing, particularly a parent. Even if the family member was not buried on the same day on which he died, the Yartzeit is observed on the date of the passing. In the first year after the passing, however, some authorities maintain that the Yartzeit is commemorated on the date of the burial, and thus one should consult with his Rabbi for guidance should such a case arise, Heaven forbid.
