Adhik Maas: The Extra Month That Stops the Hindu Calendar Drifting

The Hindu Panchang tracks two things simultaneously: the Moon's orbit around the Earth and the Earth's orbit around the Sun. A lunar month, one full cycle of the Moon, lasts roughly 29.5 days. Twelve of those add up to about 354 days. The solar year, the time it takes Earth to complete one orbit, is approximately 365.25 days. That gap is eleven days per year. Leave it uncorrected and the festivals tied to seasons, Holi to spring, the harvest celebrations to autumn, slide backward through the calendar until they are occurring in the wrong season entirely. Within seventeen years, an uncorrected lunar calendar drifts by nearly six months.

The correction is elegant. The Panchang defines a lunar month by which solar month the Moon's cycle falls inside. Each solar month corresponds to the Sun moving through one of the twelve signs of the zodiac, a Rashi. In a normal year, every lunar month contains at least one Sankranti, the moment the Sun crosses from one Rashi into the next. When the lunar month is short enough that the Sun does not complete a Rashi crossing within it, that month has no Sankranti of its own. It is declared an extra month: Adhik Maas, also called Purushottam Maas or Mala Maas depending on the tradition. The following lunar month takes the same name as the regular month it precedes, and the calendar absorbs the accumulated drift. The mechanism recurs roughly every 32.5 months, a cycle the ancient astronomer Lagadha described in the Vedanga Jyotisha, one of the earliest surviving Indian astronomical texts.

The Julian calendar, and later the Gregorian, handled the same eleven-day drift by inserting a single day every four years, the leap day. The Panchang inserts an entire month every two to three years. Both are approximations of the same underlying fact: the solar year is not a whole number of lunar months. The Metonic cycle, named after the Greek astronomer Meton of Athens who recorded it around 432 BCE, states that 235 lunar months fit almost exactly into 19 solar years. Indian astronomers worked with the same relationship. The Surya Siddhanta, a classical Sanskrit astronomical treatise, gives a figure for the length of the solar year that is accurate to within a few seconds. Adhik Maas is not superstition dressed as astronomy. It is the practical output of careful sky-watching over centuries.

Because the extra month has no Sankranti, no solar transition, it sits outside the normal ritual calendar. Weddings, thread ceremonies, and other auspicious rites governed by solar positions are traditionally not held during it. The month is instead associated with devotion, reading of texts, and acts of charity, practices that do not depend on a solar alignment. The name Purushottam Maas, meaning the month of the highest being, comes from a story in the Bhagavata Purana in which the extra month, initially considered inauspicious because it lacked a presiding deity, was taken under the protection of Vishnu himself. The astronomical fact and the mythological framing grew together: the month exists because of a gap in solar coverage, and the religious tradition filled that gap with a different kind of significance.

The Panchang remains a functioning astronomical calendar, not merely a ritual one. The dates it produces for eclipses, planetary positions, and the timing of Sankrantis are computed from the same orbital mechanics that underlie modern ephemerides, the tables of planetary positions used by observatories. ISRO's mission planners work in SI units and use modern computational models, but the sky they are computing is the same sky the Vedanga Jyotisha was describing. Adhik Maas is the visible join between two counting systems, lunar and solar, that are genuinely incommensurable. The extra month is the calendar admitting, honestly, that the Moon and the Sun do not divide evenly into each other, and correcting for that fact rather than ignoring it.