Trayodashi is the Sanskrit word for "thirteen", and is the thirteenth day in the lunar fortnight (Paksha) of the Hindu calendar. Each month has two Trayodashi days, being the thirteenth day of the "bright" (Shukla) and of the "dark" (Krishna) fortnights respectively. Thus Trayodashi occurs on the thirteenth and the twenty-eighth day of each month.

• Dhanteras, also called Dhantrayodasi, is the first day of Diwali.^[1] It occurs on Trayodashi in the month of Ashvin.