The Jain calendar, also known as the Jaina calendar or the Vira Nirvana Samvat calendar, is a lunar calendar system used by the Jain community. The Jain calendar is based on the cycles of the moon.

The Jain calendar has 12 months, and each month is either 29 or 30 days long. The first month of the Jain calendar is called Kartik and usually falls in October or November in the Gregorian calendar.

The Jain calendar is used to determine the dates of Jain festivals and events, including Mahavir Jayanti, which is the birthday of Lord Mahavir, the 24th and last Tirthankara (spiritual teacher) of the Jains. Mahavir Jayanti is celebrated on the 13th day of the bright half of the month of Chaitra, which usually falls in March or April in the Gregorian calendar.

The Jain calendar is approximately 57 years ahead of the Gregorian calendar, which is the calendar system used in most parts of the world. This means that the dates of Jain festivals and events do not correspond to the same dates in the Gregorian calendar each year. For example, Mahavir Jayanti, which falls in March or April in the Gregorian calendar, falls on a different date in the Jain calendar each year.