Data Sources

Time zone data

All zone arithmetic uses the IANA Time Zone Database (tzdata) as shipped by your browser's JavaScript engine and by Node.js at build time. City-to-zone assignments in our dataset follow the same database.

City and country data

The list of >300 cities — names, countries, coordinates, locales and currencies — was compiled by the site authors from public reference information and is maintained in the project repository. Coordinates are city-center approximations for astronomy and display, not surveying data.

Public holidays

Holiday calendars are generated from each country's published statutory rules (for example, 5 U.S.C. §6103 for United States federal holidays, GOV.UK bank-holiday guidance for England & Wales, and Japan's Public Holiday Law), plus officially announced dates for lunar-calendar holidays in South Korea. Countries and years that cannot be verified are not published. Last reviewed: 2026-07-26.

Sunrise and sunset

Solar times are computed locally using the NOAA Solar Calculator equations (based on Jean Meeus, Astronomical Algorithms). No external API is called.