Methodology & Trust
Why Do Panchang Sites Show Different Dates? Six Honest Reasons
Two reputable panchang sites can give you different festival dates, tithi end times and muhurat windows — and both can be 'right' under different classical conventions. The reasons are ayanamsa, the sunrise definition, the prevailing-tithi rule, geography, lunar-month conventions and hand-entered tables. Here is what each one changes, and what Bela pins down.
You check Diwali on three websites and get two different dates. A marriage muhurat your family pandit approves is missing from a national portal. Rahu Kaal differs by twenty minutes between apps. The usual suspicion is that someone is sloppy. The truth is more interesting: a panchang is not a fact but a computation under chosen conventions, and there are at least six places where honest, competent publishers legitimately diverge.
1. The ayanamsa
All sidereal positions depend on the ayanamsa — the offset between the tropical and sidereal zodiacs. Lahiri (the Indian government’s official choice), Raman and KP ayanamsas differ by minutes of arc, and a tithi or nakshatra whose end falls near a day boundary flips its civil date when you change that offset. Two engines, both correct, different answers. Bela pins Lahiri, and says so on every page.
2. The definition of sunrise
Almost every daily timing — Rahu Kaal, choghadiya, Abhijit — is anchored to sunrise, yet “sunrise” has at least two classical readings: the upper limb of the disc appearing, or the disc’s centre crossing the horizon, with or without atmospheric refraction. The choices differ by a couple of minutes at Indian latitudes, and every downstream window inherits the shift. Bela uses the disc-centre crossing with refraction, the standard drik-ganit definition.
3. The prevailing-tithi rule
Festivals are the loudest source of disagreement, and the cause is usually this. A lunar festival asks “which tithi prevails?” — but when you look is a convention: at sunrise, at sunset (pradosh), at midday (madhyahna), or at midnight (nishita), depending on the festival. Diwali takes the Amavasya prevailing at sunset; Janmashtami looks to midnight; Ganesh Chaturthi to midday. A site that applies one blanket rule to every festival will disagree with a site that applies each festival’s own rule — and in years where the tithi straddles the boundary, the printed date moves by a day. Our festivals list computes each festival under its own classical rule and prints the basis with it.
4. Geography and time zone
Tithis end at absolute instants; the civil date that instant lands on depends on your longitude and your clock’s offset. A tithi ending at 1 AM IST ends the previous evening in New York. Muhurat windows, keyed to local sunrise, shift continuously with geography — Kolkata’s Abhijit Muhurat starts over 40 minutes before Delhi’s. A national list computed for one city is an approximation everywhere else, which is why Bela’s city panchangs are computed per city, and the app recomputes for your exact coordinates.
5. Lunar month conventions and adhik maasa
North Indian panchangs are mostly amanta (the month ends on the new moon); many Deccan traditions are purnimanta (ending on the full moon), so the month name attached to the same day differs. Worse, in years with an adhik maasa — the intercalary leap month, 17 May to 14 June in 2026 — festival tables keyed to the solar month can fire one lunar phase early. This is a real, current example: some engine tables place Vijayadashami in 2026 on 20 September, while the popular Ashwin-based date is 20 October. Publishers who resolve the leap month differently print different dates, each defensible.
6. Hand-entered tables vs live computation
Finally, the quietest divergence: much of the web’s panchang data is typed from printed almanacs. Tables inherit printing errors, get transcribed wrong, and silently assume one city’s sunrise. A deterministic engine — Bela computes planetary positions from the Swiss Ephemeris with mean lunar nodes, and derives every window arithmetically — cannot drift that way; it can only be wrong systematically, under conventions it must then state openly.
What Bela pins down
Our choices, stated so you can hold us to them:
- Lahiri ayanamsa, mean nodes — the official Indian convention.
- Disc-centre sunrise/sunset with refraction — standard drik ganit.
- Festival-wise prevailing-tithi rules — sunset for Diwali, midnight for Shivaratri, midday for Ganesh Chaturthi, and so on, with the basis printed per festival.
- Per-city computation for 50 cities across India and the diaspora, exact coordinates in the app.
- No hand-entered tables — every number on the site is engine output.
The full statement lives on our methodology page. The mature response to “why do sites disagree?” is not to find the one true site; it is to prefer publishers who tell you their conventions — and to check any life-sized decision against your city’s panchang and a computed muhurat list rather than a forwarded screenshot. The Bela app exists to make that the easy option.
Your moment, computed for you.
Generic lists clear the universal rules. The Bela app recomputes every window for your exact city and applies Tara Bala and Chandra Bala against your own birth star — the personal layer no article can.