Every date and timing on this site is calculated from astronomical models, not copied from an almanac. This page explains the choices behind those numbers so you can judge how far to trust them.
Ayanamsa
Chakra uses the Lahiri (Chitrapaksha) ayanamsa to convert tropical planetary positions to sidereal ones. Lahiri is the ayanamsa adopted by the Calendar Reform Committee for the Indian national calendar and is the reference used by most widely followed Indian panchangs, so choosing it keeps our tithi and nakshatra boundaries in line with what people are used to seeing.
Ephemeris
Planetary and lunar positions come from the VSOP87 / ELP series as
implemented by the astronomy-engine library. The full ephemeris for the
covered years is evaluated once at build time and baked into the site — the
pages you read are static. Accuracy is on the order of one arc-minute for
the Sun and Moon over this period, which is more than enough to place tithi and
nakshatra transitions to the correct minute. Chakra does not use the Swiss
Ephemeris.
Sunrise, sunset and moonrise
Sunrise and sunset use the NOAA solar-position algorithm with the standard geometric zenith of 90.833° (−0.833°), which accounts for the Sun's apparent radius and average atmospheric refraction at the horizon. Moonrise and moonset follow the method in Meeus, Astronomical Algorithms, chapter 47, iterated for the Moon's rapid motion. All of these are computed for the exact latitude and longitude of the city you pick.
The day boundary
All five angas — tithi, nakshatra, yoga, karana and vaara — are reported as the value prevailing at local sunrise for the chosen city. This is the convention used by drikpanchang.com and by most Indian almanacs: the tithi "of the day" is whichever tithi is running when the Sun rises, even if it changes an hour later.
Masa and adhika masa
The lunar month is indexed amanta (new-moon to new-moon) as the primary scheme; the purnimanta name, where it differs, is shown as a relabel of the same underlying month rather than a separate calculation. Adhika (intercalary) months are detected and flagged. Monthly vrats still resolve to a date inside an adhika masa; other festivals are held in the corresponding nija (regular) month, matching common practice.
Tithi at sunrise versus viddha
Vrat dates use the smarta / viddha rule by default — the rule that picks the day on which the required tithi is present at the relevant reference time rather than simply the day it touches sunrise. This matches the majority of vrat listings in drikpanchang. Where a tradition splits (for example Smarta versus Vaishnava Ekadashi), Chakra follows the smarta list.
Known limitations
Chakra's festival resolver matches drikpanchang's New Delhi dates exactly for the 2026 reference year and for the large majority of a 2024–2030 cross-check. A small set of dates — about sixteen festival-years, each off by at most one day — differ because they need a finer classical test than the current rules implement:
- Bhadra-aware shifts. Holika Dahan and, in some years, Raksha Bandhan are moved off any day whose relevant window falls in the Bhadra karana. Chakra does not yet implement a Bhadra-aware selector, so in those years it can be a day early.
- Two-evening pradosh tiebreaks. When the deciding tithi covers the evening (pradosh) on two consecutive days, some years' Diwali and Dhanteras observances take the second evening; Chakra's current selector takes the first.
- Holi. Chakra reads Holi directly from the tithi at sunrise on Chaitra Krishna Pratipada, without coupling it to the preceding Holika Dahan evening, so in a few years (2024, 2025, 2027) it can land a day off.
- Nishita proxy for Janmashtami and Maha Shivratri. These depend on the tithi at true solar midnight (nishita); Chakra approximates that with the post-sunset window, which is off by a day in the years where the two disagree.
- Viddha edge cases. A few dates (for example some years of Karva Chauth, Ram Navami, Rath Yatra) sit on a near-even split between two candidate days.
- Pitru Paksha is not yet listed as its own entry. The resolver currently handles observances that key off a single tithi moment or a fixed count of days; Pitru Paksha is a sixteen-day span between two tithis, which it does not yet model.
These edges are tracked and corrected over time. For the authoritative, continuously updated dates — including per-city timings — use the Chakra app.
Coverage
Dates are available for 2020 through 2100. Time-zone conversions use the IANA time-zone database, so historical and future DST rules are applied per city.
Reporting a correction
If a date here disagrees with a panchang you trust, tell us which festival, which year and which source, and we will check it — open an issue at github.com/harshmittal2810/chakra/issues.