Shannavathi in Sanskrit means Ninety Six.
1) Number of Shraddham or Tharpana per year:
Shannavathi - 96 days when Shraddham or atleast Tharpana is to be performed.
The following are the 96 days:
Amavasya - 12
Masapirappu (Sankramanas) - 12
Pournami - 12
Kruthayugathi - 1
Threthayugathi - 1
Dwaparayugathi - 1
Kaliyugathi - 1
Vaithruthi Yogas - 14
Vyatheepatha Yoga -14
Ashtaka - 4
Anvashtaka - 4
Apart from the listed days above, one has to perform the Tharppanam on the Eclipse days and also on the next day to Mathru/Pithru Srardha days.
According to the Vaidhyanatheeyam and Srivaishnava Deepika, a dutiful Brahmin has to perform 96 tharppanams in a year, as stipulated in the Vedic scripts. Listed above are the days on which a Brahmin has to perform his duty in Thila tharpana roopam. Out of these, the Mahalaya Tharpanam can be done with Hiranyam or with Brahmmana bhojanam also; if not on all the sixteen days, any one day that one considers himself as most important – viz. Mahabharani, Madhyashtami or on his mathru/ pithru srardha thithi days that falls during Mahalayam.
If one cannot afford to perform the Tharsha Srardham known as Thila tharppanam on all the above days, one should stick to minimum possible on Amavasya, Mesha Sangramanam, Dakshinayana punyakaalam, Thula Vishu Punyakalam, Utharayana punyakalam, Mahalaya Tharpanam (one day), Visible Surya/Chandra Grahana days and also on the next days to Mathru/Pithru srardha.
2) Shraddham and Tharpana in life time:
(i) Pinda Tharpanam at Badrinath:
The Pinda Tharpanam at Brahma Kapalam, Badrinath is to be done atleast once in life time by all.
(ii) Shraddham and Tharpanam at Gaya:
The following are to be performed atleast once in life time by all at Gaya.
a) Pinda and Thila Tharpanam at the riverbed Falgu
b) Pinda Tharpanam at Vishnupadam
c) Shraddham at Gaya
d) Pinda Tharpanam at Akshayavada