1 September 2026

Why Some Assamese Festivals Move Every Year (and Others Don't)

Bohag Bihu lands on almost the same date every year. Durga Puja and Diwali don't. Here's the plain-language reason why, and how to tell which is which before you plan around them.

If you've ever tried to plan a trip around Bihu and a trip around Durga Puja, you've probably noticed something odd: one festival seems to sit on almost the same date every year, while the other jumps around by weeks. That's not inconsistency — it's two completely different calendars running underneath Assam's festival year, and once you know which one a festival belongs to, you can predict roughly when it'll land without checking a calendar at all.

The Short Answer: Two Different Calendars

Assam's festivals split into two families. One group follows the Sun — these are the solar festivals, and they land on almost the same Gregorian date every single year. The other group follows the Moon, and because a lunar month doesn't line up neatly with a solar year, these festivals drift earlier or later by as much as a month, year to year.

Solar Festivals: Steady by Design

The three Bihus — Bohag, Kati, and Magh — are all tied to solar transitions called Sankranti, the moment the sun crosses into a new zodiac sign. Bohag Bihu marks the sun entering Mesha (Aries), which happens around April 14th every year without fail. In 2026 that's April 14, with the public holiday falling on April 15. Magh Bihu tracks Makar Sankranti, landing around January 14-15 (January 15 in 2026). Because these are tied to the Earth's actual orbit rather than the Moon's phases, they almost never drift by more than a day.

Lunar Festivals: Built to Move

Durga Puja, Diwali, and Janmashtami follow the Hindu lunisolar calendar instead, where months are defined by the Moon's cycle and only loosely reconciled with the solar year. That's why Durga Puja 2026 falls in mid-October (Maha Ashtami on October 19), but in other years it can land anywhere from late September to mid-October. Diwali works the same way — it's always the new moon of the Kartik month, which is why 2026's Diwali lands on November 8 while other years put it in late October.

How This Site Marks the Difference

Rather than making you guess, every date on this site carries a quiet signal: fixed, solar-based dates are listed with confidence, and anything riding on the lunar calendar gets a 'Provisional' badge until it's confirmed closer to the date. If you're planning travel or time off around a festival, that badge is your cue to double-check nearer the day — especially for anything more than a few months out.

The short version: if it's a Bihu, pencil it in with confidence. If it's Durga Puja, Diwali, or Janmashtami, treat the date as a solid estimate and confirm it again a month or two out.