What powers the times, dates, and daylight-saving statements on this site, and where our map and city data come from.
Every time shown in the app itself is computed with the browser's own Intl API. That API reads the IANA time zone database bundled with your browser or operating system, so its rules update whenever your browser or OS does. The app never ships its own table of UTC offsets or daylight-saving rules; it defers entirely to the device it runs on.
The reference pages you are reading now (a page for each city, country, time zone, and pair of places) are rendered by our own server, which has the IANA time zone database compiled into its Node.js runtime. Every page's footer names the exact database version that produced it. The app and these pages agree almost always; they can briefly disagree only in the narrow window after a time zone rule changes somewhere in the world and before both your browser/OS and our server have picked up the update.
We do not guess whether a time zone observes daylight saving from a label or a rule of thumb. Every daylight-saving sentence on these pages, including the exact dates when the gap between two places narrows or widens, is computed by walking the actual offset timeline of the zones involved over the next 12 to 24 months and finding where it changes. A city-to-city page states the concrete window in which the gap between two places differs from usual, with real dates, rather than a generic warning that a gap "may change". Every build runs over 230 automated checks against real tzdb edge cases, including Casablanca's Ramadan clock changes, Chatham's 45-minute offset and Lord Howe Island's half-hour shift.
Some countries in our database span more than one time zone. Their pages show one representative city per distinct clock, and every time shown is attributed to the city it is actually true for. We never state a single time as if it were a fact about a whole multi-zone country: a country's headline time is always about its reference city, and that city is named.
Internally, every location is identified by its canonical IANA zone id (for example Europe/Athens), never by an abbreviation. Abbreviations such as EST, CST, or IST are display labels computed for the current date. Some of these letters are ambiguous: CST, IST, BST, and PST are each used in more than one part of the world for a different UTC offset. A page about one of these abbreviations says explicitly which meaning it is showing and names the other places that use the same letters. See our full list of time zone abbreviations for the complete set.
The colored time zone regions on the map come from data/tz-zones.geojson, derived from the timezone-boundary-builder project's boundary data and simplified for size. It was last regenerated in July 2026.
Every link this app has ever generated for sharing a view keeps working. We support two link formats, an older one and the current, more readable one, and both are decoded forever: a link someone sent you years ago will still open to the same view today.
No published corrections yet. When a reader report leads to a fix, it will be listed here with the date and the pages affected.
If a time, a date, or a description on these pages looks wrong, we want to know: write to [email protected]. Before you do, it is worth comparing the database version named in the page's footer with the latest IANA release: a very recent rule change can take a short while to reach our server or your device.