Sources and limits

City list — GeoNames (CC BY 4.0)

The 268 cities (174 countries and territories, 199 time zones), their coordinates, populations and time zone assignments come from the GeoNames cities15000 export by GeoNames, licensed under the Creative Commons Attribution 4.0 licence. This site selected the cities (national capitals, the largest city of large countries, major English-speaking business cities and cities on unusual offsets), shortened a few names (New York City → New York, Frankfurt am Main → Frankfurt) and dropped duplicates of the same metropolitan area. No endorsement by GeoNames is implied.

Clock times — IANA time zone database

Offsets, daylight-saving rules and zone names come from the time zone database built into your browser (and into Node.js when the pages were built), which follows the IANA tz database. The planner fetches nothing from a time service. When a government changes its clocks at short notice, an older browser can be wrong for that country until it updates.

Which pages exist

Pair pages were chosen by measuring Google search suggestions for “time difference between A and B” (1005 pairs, measured 2026-10-10): a pair gets a page when at least 10 suggestions name both cities, and only one page is kept for pairs whose clocks behave identically all year — 66 pages. City pages exist for cities that appear in those pairs and have at least 8 suggestions for “city time zone” (22 pages).

What the planner cannot know

Public holidays, local weekends other than Saturday–Sunday, and individual schedules. Working hours default to 9:00–17:00 and are only as right as the hours you set. Kiritimati (UTC+14) and other places with fewer than 15,000 people are not in the GeoNames file used here, so they are not in the city list.

Licence notice

Contains data from GeoNames (www.geonames.org), CC BY 4.0. Changes: selection, renaming and removal of cities as described above.