Data Sources and Methodology

We publish dates and times that people rely on, so this page explains exactly how each kind of data is produced.

Public holidays

• Fixed-date and rule-based holidays (for example Christmas, Thanksgiving, Easter Monday, King's Birthday) are calculated for any year from the published rules.
• Hindu festivals are calculated for every year from the tithi rules used in north Indian panchangs (lunar month, tithi and the time of day it must cover, such as sunrise, midday, evening or midnight), skipping Adhik months. Where an official Government of India list exists, its dates replace the calculated ones. Islamic dates show as "Expected" until the official date is added.
• State and regional holidays are not yet covered.

Hindu Panchang

Tithi, nakshatra, yoga and karana are calculated with the Sun and Moon algorithms from Jean Meeus, Astronomical Algorithms (59-term lunar series, nutation and Delta T) and the Lahiri ayanamsa, for the sunrise of the selected city. Times are usually within 1 to 2 minutes of printed panchangs.

Astronomy

Sunrise, sunset, twilight and moonrise use standard solar and lunar position formulas with atmospheric refraction. Moon phases, equinoxes and solstices are computed from the same model and are accurate to within minutes. Planet positions use the JPL approximate Keplerian elements and are accurate to about one degree. Eclipse dates and visibility come from published eclipse catalogues.

Other calendars

Islamic dates use the tabular (arithmetical) Hijri calendar on the server and the Umm al-Qura calendar in your browser; actual dates depend on moon sighting and can differ by a day. Hebrew dates use the standard Hebrew calendar rules. Other calendars use the calendar data built into your browser.

Time zones

Time zone offsets and daylight saving changes come from the IANA time zone database used by PHP and your browser.

Weather

Weather data is provided by Open-Meteo under the CC BY 4.0 licence.

Corrections

If you find a wrong date, use the Contact Us page and choose "Report a wrong date". Please include a source.

Last updated 16 October 2026