Data sources and accuracy

City data

City names, coordinates, regions and populations come from GeoNames, licensed under CC BY 4.0. We select 2,000 cities in 244 countries and territories: every capital, the largest cities in each country, and the largest cities worldwide.

Time zones

Offsets and clock-change dates come from the IANA time zone database, version 2026e, built into our time engine. Pages are rebuilt regularly so that newly announced changes appear quickly.

Accuracy

Clocks sync with our time servers the same way network time protocols do: several round trips, keeping the fastest, with the remaining uncertainty shown in the badge (for example "Locked · ±15 ms"). If a clock cannot sync, it says so and shows your device time instead.