Amanta vs Purnimanta Calendar Systems: Regional Traditions Explained
The Hindu calendar is Luni-Solar, meaning it tracks both the Moon's phase (for months) and the Sun's transit through the zodiac (for years). Across India, two major traditions define when a lunar month begins and ends: the Amanta and Purnimanta systems.
Although their month names and start dates differ, both systems are based on the exact same astronomical calculations. They are simply two different naming conventions for the same phases.
The Amanta System (New Moon Ending)
In the Amanta system (Amavasya-anta), a lunar month ends on the New Moon (Amavasya) when the solar-lunar angular separation is 0° (or 360°). The new month begins the following morning on Shukla Paksha Pratipada. This system is followed in South Indian states (Karnataka, Andhra Pradesh, Telangana, Tamil Nadu) and western states (Maharashtra, Gujarat).
The month is named after the zodiac sign (Sankranti) in which the New Moon occurs.
The Purnimanta System (Full Moon Ending)
In the Purnimanta system (Purnima-anta), the lunar month ends on the Full Moon (Purnima) when the solar-lunar separation is exactly 180°. The new month begins the next day on Krishna Paksha Pratipada. This tradition is followed in North Indian states (Uttar Pradesh, Bihar, Rajasthan, Madhya Pradesh, Punjab, Haryana).
Because the month ends on the Full Moon, a Purnimanta month begins 15 days earlier than its Amanta counterpart. The Krishna Paksha (dark fortnight) begins the Purnimanta month, whereas the Shukla Paksha (bright fortnight) begins the Amanta month.
Mathematical Equivalence of Fortnights
The two systems share the exact same fortnights (Pakshas). The Shukla Paksha (bright fortnight) of a month has the same name and dates in both calendars. The Krishna Paksha (dark fortnight) simply belongs to different months. Specifically, the Krishna Paksha of a Purnimanta month is identical to the Krishna Paksha of the preceding Amanta month.
For example, Krishna Janmashtami falls on Krishna Paksha Ashtami. In the Purnimanta system, this occurs in the month of Bhadrapada. In the Amanta system, it occurs in the month of Shravana. Both systems point to the exact same astronomical day. Thus, there is no discrepancy in the planetary alignments or festival celebrations; they are mathematically equivalent.