In a Jain panchang, tithi means the lunar day. There are 30 tithis in a full lunar month:

Shukla Paksha tithis

These are the waxing moon days:

1. Pratipada
2. Dwitiya
3. Tritiya
4. Chaturthi
5. Panchami
6. Shashthi
7. Saptami
8. Ashtami
9. Navami
10. Dashami
11. Ekadashi
12. Dwadashi
13. Trayodashi
14. Chaturdashi
15. Purnima

Krishna Paksha tithis

These are the waning moon days:

1. Pratipada
2. Dwitiya
3. Tritiya
4. Chaturthi
5. Panchami
6. Shashthi
7. Saptami
8. Ashtami
9. Navami
10. Dashami
11. Ekadashi
12. Dwadashi
13. Trayodashi
14. Chaturdashi
15. Amavasya

In simple words

• 1 to 15 = Shukla Paksha
• 16 to 30 = Krishna Paksha
• The 15th tithi is:

- Purnima in Shukla Paksha - Amavasya in Krishna Paksha

In Jain tradition, many vow days, fasting days, and religious observances are based on these tithis, especially Ashtami, Chaturdashi, Purnima, and Amavasya.