Method
Data sources & method
Where our numbers come from — and why they're correct.
Time zones and daylight saving
All offsets and daylight saving rules come from the IANA Time Zone
Database (tzdata) — the authoritative source that operating
systems, programming languages and browsers themselves build on. We never
hardcode an offset. Instead we ask the browser's built-in
Intl.DateTimeFormat to translate one concrete moment into
local time for a given IANA zone, such as Europe/London or
America/New_York. Because the calculation is done for a
specific instant rather than a general rule, the answer is correct in
summer, in winter, and in the few weeks when two countries have switched
on different dates and the difference is temporarily an hour off.
Geodata
City names, coordinates and population figures come from GeoNames and are used under the CC BY 4.0 license. Each city is mapped to its correct IANA zone ahead of time, which avoids the mapping mistakes common elsewhere — cities placed in the wrong country or the wrong zone.
Flags
Country flags are vendored from flagcdn.com (public domain) and served from this site — they never trigger a request to a third party.
Privacy of the method
Content pages make no third-party requests: times are computed locally in your browser, and all assets are served from this site. Analytics and ads load only after consent — see the privacy policy for the details.
Found something wrong?
If a time or a place looks off, write to us via the contact page and name the city or country — we'll fix it.