In vedic timekeeping, a tithi (also spelled thithi) is a lunar day, or the time it takes for the longitudinal angle between the moon and the sun to increase by 12°. Tithis begin at varying times of day and vary in duration from approximately 19 to approximately 26 hours.

There are 30 tithis in each lunar month, named as follows:

Ekadasi, the eleventh day of each lunar fortnight, has special religious significance in Hinduism and Jainism -- usually observed by fasting.