Questions we are asked most

Panchang is the traditional Hindu calendar system that tracks five elements: Tithi (lunar day), Nakshatra (lunar mansion), Yoga (sun-moon angle combination), Karana (half-tithi), and Vara (weekday). It also includes muhurat (auspicious timings), sunrise/sunset, and festival dates.

We use Swiss Ephemeris with Lahiri ayanamsa, and kala definitions following Dharmasindhu and Nirnayasindhu conventions. Verification runs in three tiers on every build: Tier A compares 7 festivals across 1950–2100 against DrikPanchang (42/42), Tier B locks an every-day hash across 8 years to catch silent drift, and Tier C replays 22 days of a production accuracy audit (26/26). The suite is 152 tests at 91% coverage. Our known limitations are published on the Accuracy page.

Explainability means every API response includes reasoning — not just a result, but the derivation chain that produced it. For festivals, we show which rule was applied, which authority it came from, and the astronomical basis. This transparency is unique to TathaAstu.

The Festival Engine is our derivation system that computes festival dates from first principles — astronomical positions → panchang elements → festival rules → calendar dates. It uses a multi-authority hierarchy (Kala Vyapini) with explainable outputs and versioned rules.

Yes. The Free plan includes 500 requests per month with access to the Panchang and Festival APIs, and no card is required. Confidence scores and the engine version envelope are included on every plan, including Free.

Anywhere in the world. Send lat and lon — for example lat=48.8566&lon=2.3522 — and the Panchang, muhurat and festival dates are computed for that location and returned on its local clock, with daylight saving applied from the IANA database. The timezone is worked out from the coordinates, so you do not have to supply one; you can still pass tz=Europe/Paris to state it explicitly, which is worth doing when you already know the user's zone or their coordinates sit near a border. Fifteen South Asian locations (New Delhi, Mumbai, Chennai, Kolkata, Bengaluru, Hyderabad, Varanasi, Ujjain, Haridwar, Ayodhya, Guwahati, Srinagar, Ahmedabad, Kathmandu, Colombo) are additionally precomputed and can be requested by location_id.

Yes, and the API handles it. A tithi begins and ends at a single global instant, but a Hindu day is bounded by local sunrise — so which civil date a festival lands on depends on where you are. Raksha Bandhan 2026 falls on 28 August in Delhi and Sydney but on 27 August in Paris and New York. Pass lat, lon and tz to /v1/festivals and you get the occurrence date for that location. Never add or subtract a day yourself.

No. Send the coordinates and every time in the response — sunrise, sunset, rahu kaal, choghadiya and muhurat windows — is already on that location's local clock, with DST resolved from the IANA timezone database. Pass tz=America/New_York if you want to name the zone yourself. Abbreviations like IST, EST or PST are rejected: EST is a fixed-offset legacy entry that never applies daylight saving, so it would silently be an hour out for much of the year. The response states which zone was used and whether it came from your tz parameter or from the coordinates.

Free: 500 req/month. Starter: 100K req/month. Pro: 1M req/month. Enterprise: unlimited. Rate limits are enforced per API key and reset according to your plan period.

Create a free API key from the dashboard, then send a request with an X-API-Key header. The developer quickstart walks through four steps, ending with an explained festival response. You can also try every endpoint in the playground without an account.

Yes. Our API supports 50+ languages for transliterations. Tithi, nakshatra, yoga, and festival names can be returned in Hindi, Sanskrit, Tamil, Telugu, and many more languages.

Kala Vyapini is our multi-authority rule hierarchy for festival derivation. Instead of relying on a single source, we reference multiple authoritative texts and modern references, with a clear conflict-resolution chain. This ensures accurate and culturally appropriate festival dates.