Kalpadi Tithi is the starting of a day of Brahma. A day of Brahma is equal to 4,320,000,000 human years. There has been several Kalpas. At the end of a Kalpa there is the cosmic flood which marks the end of a cycle of creation. Then it is the night time of Brahma. The cycle of creation again begins on a Kalpadi Tithi.
Kalpadi Tithis are
Chaitra Shukla Paksha Pratipada – Yugadi
Chaitra Shukla Paksha Panchami
Chaitra Shukla Paksha Tritiya
Kartik Shukla Paksha Saptami
Margashirsh Shukla Paksha Navami
Magh Shukla Paksha Trayodasi
Falgun Shukla Tritiya
It is considered highly meritorious to perform Shradh and Tarpan rituals on Kalpadi Tithis.