Samvatsrikam is a shradh performed around the 1st death anniversary of the deceased. It is a three days ceremony concerning various rituals of Unabdikam, Samvatsaravimoka and Abdikam.
Unabdikam is a shradh performed two days before abdikam.
Samvatsrikam or Samvatsaravimoka is the shradh performed one day before abdikam. Abdikam is performed on the tithi of departure.
Thus all the sixteen Māsikams with Ābdikam should be performed. These all are eternal duties which should not be omitted.
After performing these Śrāddhams, Prātisāmvatsarīkam should also be performed in each year. In case if someone is not capable to perform all these Śrāddhams due to some unavoidable conditions or incapability he can then perform at least three Śrāddhams from the day of Ūnābdikam to Ābdikam. He has to do include all omitted Śrāddham on the day of Ūnābdikam.
After performing these Śrāddhams, Prātisāmvatsarīkam should also be performed in each year.