Time Zone Converter, Compare Times Across Cities
Convert a date and time between any time zones at once. Daylight saving handled, next-day shifts flagged, and everything runs in your browser.
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A time zone converter answers a very specific question: if it is this time here, what time is it there? You pick a date and a time in one zone, add the cities or zones you care about, and every one of them is shown side by side with its own local date, its UTC offset and how far ahead or behind it sits. That is the everyday problem behind scheduling a call with a colleague in another country, joining a webinar advertised in a foreign time zone, planning a flight arrival, catching a live stream, or setting a deadline that means the same moment to everyone involved.
Frequently asked questions
Does this handle daylight saving time correctly?
Is my data sent anywhere?
Why should I pick a city instead of an abbreviation like EST or CST?
What does the "next day" tag mean?
Why is the difference between two cities not the same all year?
Can I convert to UTC?
Are half-hour and 45-minute offsets supported?
How do I plan a meeting for a group in different countries?
Which zone does it use by default?
About Time Zone Converter, Compare Times Across Cities
The hard part of time zone conversion is never the arithmetic, it is the exceptions. Daylight saving time shifts many zones by an hour twice a year, but not on the same dates: the United States and Europe switch weeks apart, and the southern hemisphere moves in the opposite direction, so the gap between, say, London and New York is not constant through the year. Plenty of zones do not observe daylight saving at all, including most of Asia and Africa, all of Japan and India, and the American state of Arizona. Some offsets are not whole hours: India is UTC+5:30, Nepal is UTC+5:45, and parts of Australia use UTC+9:30. And crossing the date line means the answer is often on a different calendar day, which is why this tool flags "next day" or "previous day" instead of quietly showing a time that looks plausible but is 24 hours out.
This converter avoids guessing by using your browser's own copy of the IANA time zone database through the Intl API. That database is the same authoritative dataset used by operating systems and servers, and it encodes the historical and current daylight saving rules for every zone, so a conversion for a date in March or October lands on the correct side of the switch. Choosing a proper zone identifier such as Europe/Lisbon or America/Sao_Paulo rather than an abbreviation is deliberate: abbreviations are ambiguous (CST is used for both North American Central Standard Time and China Standard Time) while zone identifiers are not.
To use it, set the source zone (your own is preselected), pick the date and time, then search for the zones you want to see. Your target list is saved in your browser so it is still there next visit, you can switch between 24-hour and 12-hour display, jump a day forward or back, promote any target to be the new source with one click, and copy the whole comparison as plain text to paste into an email or a chat message. Nothing is sent to a server, no account is needed, and the page keeps working offline once loaded.
Railways Invented the Time Zone
Before the 1800s every town simply kept its own solar time, setting noon by when the sun was highest overhead. Since that moment arrives a few minutes later for each degree of longitude you travel west, Bristol ran about ten minutes behind London and no one minded, because nothing moved fast enough for the difference to matter. Railways changed that overnight. Trains crossing dozens of local times made timetables incoherent and, more seriously, made collisions likely on single-track lines where scheduling was the only safety mechanism.
Britain's Great Western Railway adopted London time across its network in 1840, and the practice spread as "railway time". North America went further in 1883, when the railroads carved the continent into standard zones on their own authority, a year before governments got involved. The following year the International Meridian Conference in Washington chose Greenwich as the prime meridian, largely because most of the world's shipping already used charts based on it, and the framework of hourly offsets from Greenwich followed. France held out for decades, officially defining its time as "Paris mean time retarded by nine minutes and twenty-one seconds" rather than admit it was using Greenwich.
Today the system is still stubbornly political rather than geometrical. China spans five geographic hours yet runs a single official zone, so the sun can rise after 10 am in the far west. Nepal chose a 45-minute offset partly to distinguish itself from India. Spain sits on Greenwich longitude but keeps central European time, a wartime alignment with Germany that was never undone and is often blamed for the country's late meals. Samoa skipped 30 December 2011 entirely, jumping across the date line to trade with Australia and New Zealand more easily, and Kiribati had already bent the line eastward in 1995 to keep the country on one calendar day. All of this messy history is recorded in the IANA time zone database, maintained by volunteers since 1986 and quietly relied upon by nearly every computer on earth, including the browser you are reading this in.