Adhika masa: the leap month

Twelve Moons and a year

A lunar month, from one new Moon to the next, averages about 29.53 days. Twelve of them make about 354.37 days. The Sun takes about 365.26 days to return to the same point among the stars. The difference is close to eleven days a year. A calendar of twelve lunar months alone slides through the seasons, as the Islamic calendar does by design, so that a festival kept in spring one decade falls in winter a decade or so later.

The Hindu calendar is lunisolar. Its months are lunar, but it keeps them in step with the Sun by adding a thirteenth month when needed. That month is the Adhika māsa, the "additional month", also called purushottama masa, the month of Vishnu, and in older usage mala masa, the "impure" month.

The rule: a month without a sankranti

Each lunar Māsa, counted here from one new Moon (Amāvāsyā) to the next, is named after the Saṅkrānti, the Sun's entry into a sidereal sign, that falls within it. The month in which the Sun enters Mesha is Chaitra, the month in which it enters Vrishabha is Vaishakha, and so on round the year.

Solar months, the time the Sun spends in one sign, vary from about 29.4 to about 31.5 days. They are longest in the middle of the year, when the Earth is farthest from the Sun and moves slowest. In those months a whole lunar month of 29.5 days can begin just after one sankranti and end just before the next. That lunar month contains no sankranti at all. It is declared adhika and takes the name of the month that follows, which is then called nija, "proper". In 2026, for example, an adhika Jyeshtha ran from mid-May to mid-June and was followed by the nija Jyeshtha.

Since about eleven days accumulate each year, an adhika masa comes roughly every thirty-two and a half months, seven times in nineteen years. Recent and coming cases from our computation are an adhika Shravana in 2023, the adhika Jyeshtha of 2026 and an adhika Chaitra beginning in mid-March 2029. Because solar months are long in mid-year, adhika months fall mostly between Chaitra and Ashwina.

The rare lost month

Near perihelion, in December and January, the Sun moves fastest and a solar month can be shorter than a lunar one. A lunar month can then contain two sankrantis, and one month-name is left without a month of its own. That name is "lost": a kshaya masa (see Kṣaya). This is rare, separated by intervals of decades or more than a century, and it comes with two adhika months nearby, one before and one after, so the year still has thirteen months†. Our engine finds one in the winter of 1963–64 and another early in 1983; almanacs differ in how they name the months around them†.

Old roots

The idea is old. A hymn of the Rigveda (1.25.8) praises Varuna as knowing the twelve months "and the one that is born in addition", generally read as a reference to an intercalary month. The Vedanga Jyotisha, the Vedāṅga of time-reckoning attributed to Lagadha, uses a five-year cycle with two intercalary months. The rule of the month without a sankranti, applied to the true motions of the Sun and Moon, belongs to the later siddhantic calendar†. The Calendar Reform Committee report of 1955, chaired by Meghnad Saha, gives a detailed modern account of these rules.

What happens in an adhika month

Festivals keyed to a month are kept in the nija month, not the adhika one: an adhika Shravana has no Raksha Bandhan of its own. Dharmashastra digests set aside a range of new beginnings during the adhika month, among them the sacred-thread ceremony, house-entry and other household rites, and recommend the month instead for vratas, recitation and giving†. A text in its praise, the Purushottama Masa Mahatmya, is read in many homes during it.

The adhika month also brings two extra Ekadashis, Padmini and Parama, which is why a lunar year with an adhika masa has twenty-six rather than twenty-four. And it explains the jump in festival dates: after the adhika Jyeshtha of 2026, Diwali fell on 8 November, nineteen days later than in 2025.

Why it matters for reading dates

A Hindu date in a leap year needs one more word than usual. "Jyeshtha Shukla Dashami, 2026" names two different days, one in the adhika month and one in the nija month, about thirty days apart. Almanacs and our tools add the word adhika or nija to remove the ambiguity.

Try it

The Calendar converter shows the lunar month of any date in both amanta and purnimanta reckoning and says when it is an adhika month. The Month calendar shows the tithis day by day, and the Festivals list shows how observances move after a leap month.

† Marked dates or readings are debated among scholars or still being confirmed by our faculty.