The Vedic calendar is the oldest known Indian calendar system, dating back to the 2nd millennium BCE.

The Vedic calendar is based on the lunar cycle, with each month beginning with the new moon.

A Vedic month has either 29 or 30 days, depending on the phase of the moon.

Adhika Masa is the intercalary month in the Vedic calendar, which is added every 32 or 33 months to keep the calendar in sync with the solar year.

The Saka calendar is the most widely used Indian calendar system today, and is used in many parts of India, Nepal, and Sri Lanka.

The Saka calendar is based on the solar cycle, with each year beginning with the spring equinox.

A Saka year has 365 days, with an extra day added every four years in leap years.

Malimasa is the intercalary month in the Saka calendar, which is added every 32 or 33 months to keep the calendar in sync with the solar year.

The Vikrama Samvat calendar is the oldest known Indian solar calendar, dating back to the 1st century BCE.

The Vikrama Samvat calendar is based on the solar cycle, with each year beginning with the spring equinox.

A Vikrama Samvat year has 365 days, with an extra day added every four years in leap years.

Adhika Masa is the intercalary month in the Vikrama Samvat calendar, which is added every 32 or 33 months to keep the calendar in sync with the solar year.

The Kollam Era calendar is the oldest known Indian lunisolar calendar, dating back to the 9th century CE.

The Kollam Era calendar is based on the lunisolar cycle, with each month beginning with the new moon and each year beginning with the spring equinox.

A Kollam Era year has 365 days, with an extra day added every four years in leap years.

Adhika Masa is the intercalary month in the Kollam Era calendar, which is added every 32 or 33 months to keep the calendar in sync with the lunisolar cycle.