The Yahrzeit is observed annually on the Jewish date of death. When death occurs after sunset, it is the following day that is used to calculate the Yahrzeit.
When three or more days have elapsed from the day of death until the interment, the first Yahrzeit is observed on the anniversary of the interment.
On all subsequent years it is observed on the anniversary of the death.
The Yahrzeit begins at sunset on the preceeeding day and is concluded at sunset of the day of death. During the observance of the Yahrzeit, a memorial Yahrzeit candle is kept burning and the Mourner''s Kaddish is recited during services in the Synagogue. (from www.yahrtzeit.com )
To calculate a Yahrzeit, please use one of the following links
Simple calculator: www.yahrtzeit.com
Complex calculator: www.chabad.org
50 year yahrzeit calculator: www.shamash.org