In the Eastern Church in particular, there are certain intervals at which the faithful pray for their departed. This correspond roughly to biblical increments.
St. Simeon of Thessalonika explains that "the Third Day service is celebrated for the reason that the reposed one received his being through the Trinity." It also invokes the resurrection of Christ on the third day.
The ninth day after death is kept in remembrance of the nine choirs of angels since it is our hope that the souls of the faithful departed shall dwell with the angelic host.
The fortieth day after death hearkens back to the Old Testament. Joseph mourned his father Jacob for forty days. The Israelites also mourned for Moses for the length of forty days. Moreover, our Lord remained on earth for forty days after His resurrection before ascending to heaven.
The one year anniversary, according to St. Simeon, "is celebrated because it is the consummation, and our God, the Trinity, is the life of all and the cause of being and shall be the restoration of all the renewal of human nature."
So don't forget to pray for your beloved departed.