Hindu Calendar

A lunisolar calendar

The Hindu calendar tracks both the moon and the sun: each month (masa) runs from one new moon to the next, while an extra “leap month” is inserted every couple of years to keep the lunar year aligned with the solar seasons. Because of this, festival dates on the Gregorian calendar shift from year to year — a festival tied to a specific tithi doesn't fall on the same date every Gregorian year, which is why each festival's date is recalculated annually rather than fixed.

Paksha — the two fortnights

Each lunar month is split into two paksha (fortnights): Shukla Paksha, the waxing fortnight from new moon to full moon, and Krishna Paksha, the waning fortnight from full moon back to new moon.

Tithi — the lunar day

A tithi is one of thirty lunar days in a month (fifteen per paksha), measured by the angle between the sun and moon rather than a fixed 24-hour span — so a tithi can run slightly under or over a day, which is why the exact start and end time of a festival is calculated, not just its calendar date.

The twelve months