Time Zone Converter

How to use Time Zone Converter

1. Pick a source zone and a target zone, or add several to compare at once.
2. Set a date and time in the source zone.
3. Read the equivalent time in every other zone, with the UTC offset and DST status.

Why do time zone abbreviations cause so much confusion?

Because they are ambiguous, unstandardized, and change twice a year.

CST means Central Standard Time in North America (UTC−6), China Standard Time (UTC+8), and Cuba Standard Time (UTC−5). BST is British Summer Time (UTC+1) and Bangladesh Standard Time (UTC+6). IST covers India (UTC+5:30), Ireland (UTC+1) and Israel (UTC+2).

They also flip seasonally. "9am EST" in July is meaningless, because the US East Coast is on EDT in July — and someone reading it literally would be an hour off.

The reliable way to specify a time is an IANA zone identifier — America/New_York, Europe/London, Asia/Tokyo — which names a geographic region whose rules the database tracks. That is what this tool uses. For a one-off meeting, quote UTC alongside local time and the ambiguity disappears.

When do the clocks change?

The northern hemisphere dates differ between the US and Europe, which produces two weeks each year when the usual offset between them is wrong by an hour.

So for two weeks in March, New York is four hours behind London instead of the usual five. For one week at the end of October, it is four hours behind again. Any recurring transatlantic meeting scheduled by fixed offset rather than by zone will drift during those windows.

The EU voted in 2019 to abolish seasonal clock changes, and the US Senate passed the Sunshine Protection Act in 2022. Neither has been implemented. Both are worth knowing about if you are writing software that assumes the current rules are permanent — they are not, which is precisely why the IANA database is updated several times a year.

How do I schedule a meeting across time zones?

1. Work in the participants' zones, not offsets. Send a calendar invitation, which carries the zone and lets each client render local time correctly.
2. Find the overlap. US East Coast and Western Europe share roughly 2pm–5pm CET. US West Coast and Western Europe share only about 9am–11am PT / 6pm–8pm CET.
3. Avoid the DST transition weeks. Mid-to-late March and late October are when fixed-offset assumptions break.
4. Watch the date line. A Monday 9am call in San Francisco is Tuesday 2am in Sydney. Scheduling across it without checking the day is a common and embarrassing error.
5. Rotate the inconvenience. For a recurring meeting spanning more than eight hours of offset, someone is always taking it outside working hours. Alternate who.

What is UTC, and how does it relate to GMT?

UTC — Coordinated Universal Time — is the modern time standard, maintained by atomic clocks and used as the reference for every zone offset. It is not a time zone; it is the reference point.

GMT — Greenwich Mean Time — is a time zone (UTC+0) that the UK observes in winter. In casual use the two are treated as identical, and for civil purposes the difference is under a second.

The technical distinction is that UTC is atomic time adjusted with leap seconds to stay within 0.9 seconds of Earth’s rotation, while GMT was defined astronomically. The International Bureau of Weights and Measures voted in 2022 to stop adding leap seconds by 2035, which will let UTC drift slowly from solar time.

For scheduling, storage and APIs, use UTC. Storing local times in a database and converting on read is one of the most reliable ways to produce bugs that only appear twice a year.

Frequently asked questions