The Assamese calendar (অসমীয়া বৰ্ষপঞ্জী) is a sidereal solar calendar — it tracks the Sun's position against the fixed stars, not the moon. A month is the time the Sun spends in one zodiac sign (rashi).
The instant the Sun crosses into the next sign is a Sankranti. In the Assamese system the Sankranti day is the last day of the outgoing month, and the month lengths (29–32 days) follow how long the Sun sits in each sign, so they shift from year to year. Traditional panjikas compute the Sun by the classical Surya Siddhanta, which currently runs about a day behind modern astronomy — that is why printed dates differ from ordinary online calculators.
The year opens with Bohag (Mesha transit) in mid-April; its first day is Manuh Bihu, the Assamese New Year, and the day before (last day of Chot) is Goru Bihu. Similarly the last day of Puh is Uruka with Magh Bihu on 1 Magh, and Kati Bihu falls on 1 Kati.
Panjikas print three years side by side: Shaka (national era, +78/79 behind CE, rolls over at Bohag), Shankarabda (Sankaradeva era), and Bhaskarabda (the সাল, from King Bhaskaravarman of Kamarupa). The সাল rolls over in autumn, during Ahin — so from Ahin 2026 it reads Bhaskarabda 1434 · Shankarabda 578 · Shaka 1948. (Online sources that switch the year at Bohag/April are using a different convention.)
Weekday names follow the Navagraha. Alongside the solar date, panjikas give the tithi (lunar day) for religious timing — full moon is পূৰ্ণিমা (15), new moon অমাৱস্যা (30).
| # | Assamese | Roman | Zodiac (rashi) | Sanskrit | Typical Gregorian |
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Month boundaries use the Surya Siddhanta — the classical reckoning behind traditional Assam panjikas such as the Borkotoki Company almanac (Jorhat) — not the modern drik/Lahiri astronomy. Each Sankranti (the Sun's Surya-Siddhanta entry into a sidereal sign) is computed, and the month begins on the first sunrise at Jorhat after that moment; the Sankranti's own sunrise-to-sunrise day is the last day of the outgoing month.
This reproduces the Borkotoki panjika at every point checked: 1 Ahin = 19 Sep 2026, 1 Kati = 19 Oct, 1 Puh = 17 Dec, 1 Magh = 16 Jan 2027, Bohag Bihu = 15 Apr 2026, with month lengths Ahin 30, Puh 30, Magh 29 days — and today reads 9 Ahin, Bhaskarabda 1434.