Amanta and purnimanta: the Hindu calendar's two month systems

Where does a month end?

A lunar Māsa, or month, runs from one phase of the Moon to the same phase again, about 29.5 days. But which phase? Indian calendars give two answers.

• In the amanta system (amanta, "ending at ama", the new Moon), a month runs from the day after one new Moon to the next new Moon, Amāvāsyā. This is the reckoning of Maharashtra, Gujarat, Goa, Karnataka, Andhra Pradesh and Telangana, and of the lunar months used for festivals in Tamil Nadu and Kerala.
• In the purnimanta system (purnimanta, "ending at the full Moon"), a month runs from the day after one full Moon to the next full Moon, Pūrṇimā. This is the reckoning of much of North India, including Uttar Pradesh, Bihar, Madhya Pradesh, Rajasthan, Delhi, Haryana, Punjab, Himachal Pradesh, Uttarakhand, Jharkhand and Chhattisgarh, and of Nepal.

Bengal, Odisha and Assam use solar months for the civil year, with amanta lunar months for many festivals†.

Same fortnights, shifted names

Every lunar month has a bright fortnight, shukla Pakṣa, from new Moon to full Moon, and a dark fortnight, krishna paksha, from full Moon to new Moon. The two systems agree on every bright fortnight. They disagree only about which month a dark fortnight belongs to.

In the amanta system the dark fortnight closes the month: Chaitra's bright half is followed by Chaitra's dark half. In the purnimanta system the dark fortnight opens the month: Chaitra begins with a dark half and then has its bright half. So a purnimanta month starts about fifteen days before the amanta month of the same name, and every dark fortnight carries the name of the following month.

Fortnight, in order	Amanta name	Purnimanta name
Dark half ending at the new Moon before Chaitra	Phalguna krishna	Chaitra krishna
Bright half that follows	Chaitra shukla	Chaitra shukla
Dark half after that	Chaitra krishna	Vaishakha krishna
Next bright half	Vaishakha shukla	Vaishakha shukla

The same day under two names

Festivals are fixed by tithi and paksha, so every festival in a dark fortnight has two month-names, one for each system. The day itself does not change.

• Krishna Janmashtami is Shravana krishna ashtami in an amanta almanac and Bhadrapada krishna ashtami in a purnimanta one.
• Maha Shivaratri is Magha krishna chaturdashi (amanta) and Phalguna krishna chaturdashi (purnimanta).
• Diwali, on the new Moon, closes Ashwina in the amanta system and falls in the dark half of Kartika in the purnimanta system.
• Karva Chauth is Kartika krishna chaturthi in the purnimanta reckoning of the north, and Ashwina krishna chaturthi in amanta terms.

Festivals in a bright fortnight, such as Ram Navami (Chaitra shukla navami) or Ganesh Chaturthi (Bhadrapada shukla chaturthi), carry the same name in both. Holi, on the full Moon of Phalguna, is Phalguna purnima in both, since the full Moon ends the bright half that both systems share.

Which is older?

Both have long histories, and scholars disagree about which came first†. The siddhantic computation of a month starts naturally from the conjunction of Sun and Moon at new Moon, which suits the amanta form, and the rule for an Adhika māsa, a leap month, is defined on amanta months even in purnimanta regions. The full-Moon ending, on the other hand, is long attested in northern usage, and the month names themselves come from the Nakṣatra near which the full Moon falls: Chaitra from Chitra, Vaishakha from Vishakha, Kartika from Krittika, and so on.

Year beginnings and eras

The two systems also begin the year at different points. The Vikram Saṃvat, or era, in the north begins with the bright half of Chaitra; in Gujarat, which counts amanta months, the Vikram year begins on the first tithi of the bright half of Kartika, the day after Diwali. The Shaka era of the Deccan's lunar calendars also begins in Chaitra. The Indian National Calendar, adopted in 1957 on the recommendation of the Calendar Reform Committee chaired by Meghnad Saha, uses Shaka years with fixed solar months beginning on 22 March (21 March in leap years), a third system altogether.

The leap month in a purnimanta almanac

The adhika month is computed from new Moon to new Moon, so a purnimanta almanac has to fit it between the two halves of a regular month. In 2023, for example, a purnimanta reader met the dark half of Shravana, then the bright and dark halves of the adhika Shravana, and only then the bright half of the regular Shravana, which ended with Raksha Bandhan on its full Moon.

Reading a date

When an almanac, a website or a relative gives a Hindu date in a dark fortnight, it is worth asking which system it uses. A difference of one month in the name usually means a difference of system, not of day. Our tools show both.

Try it

The Calendar converter gives any date's month in amanta and purnimanta reckoning side by side. The Month calendar shows the fortnights across a month, and the Festivals list gives each observance with its tithi and paksha.

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