Timezone Converter & World Clock at a glance
- What it does
- Convert a time between time zones and see the current time in cities worldwide, with practical advice on scheduling across regions.
- Where it runs
- Entirely in your browser — no data is uploaded
- Works offline
- Yes, once the page has loaded
- Cost
- Free, with no account and no usage limit
- Category
- Converters
How to use the converter
- Pick a source zone and enter the time you are converting from.
- Add the zones you want to compare.
- Read the equivalents, which account for daylight saving as it applies on that date.
Daylight saving is the reason this is hard
Roughly seventy countries change their clocks, and they do it on different dates. Between mid-March and early April, the gap between London and New York is four hours rather than the usual five, because the US changes first. In autumn there is a similar window in the other direction.
The southern hemisphere is offset by half a year, so the difference between London and Sydney varies between eight, nine, ten and eleven hours over a full year. A recurring meeting scheduled once in a fixed pattern will drift out of its intended slot at least four times a year.
Much of the world does not observe it at all - most of Asia and Africa, and all of India, China and Japan. Within the US, Arizona and Hawaii do not.
Offsets that are not whole hours
Several zones sit on a half or quarter hour, which regularly breaks software that assumes integer offsets.
| Zone | Offset |
|---|---|
| India | UTC+05:30 |
| Iran | UTC+03:30 |
| Nepal | UTC+05:45 |
| Chatham Islands | UTC+12:45 |
| Newfoundland | UTC−03:30 |
| Parts of Australia | UTC+08:45, UTC+09:30, UTC+10:30 |
China is a different oddity: one time zone across a country spanning five geographic ones, so in the far west the sun rises around 10am by the clock.
Scheduling across time zones
- Name the zone, not the offset. "3pm London time" is unambiguous; "3pm GMT" is wrong for half the year, since London is on BST in summer.
- State the date. A meeting at 9pm in New York is the following day in Singapore, which is where most missed calls originate.
- Find the genuine overlap. US East Coast and Western Europe share a workable window in the early afternoon UTC. West Coast and India share almost nothing, and pretending otherwise means someone is always working at night.
- Rotate the inconvenience. If a recurring call has to be awkward for someone, alternate who it is awkward for.
- Send a calendar invitation. Calendar software handles this correctly; typed times in an email do not.
For developers
Two rules cover most of it. Store instants in UTC and convert at display time. Store an IANA zone name such as Europe/London rather than a fixed offset, because offsets change and names remain valid.
The distinction that matters: a past event is an instant, and UTC captures it perfectly. A future event is often a local wall-clock time - "9am on 15 March in Berlin" - and storing it as UTC is wrong, because if Germany changed its daylight-saving rules before then, your stored instant would no longer be 9am. Store the local time plus the zone, and resolve it when the date arrives.
The timezone database is updated several times a year as governments change the rules, sometimes with only weeks of notice. Keep your runtime's copy current.
Frequently asked questions
UTC is the modern atomic time standard; GMT is a time zone that happens to have the same offset in winter. For technical use write UTC. For London specifically, note that the city is on BST (UTC+1) from late March to late October.
India chose a single national zone centred on a longitude that falls at UTC+05:30. Several countries did the same to place a single zone sensibly across their territory.
No - fewer than half. Most of Asia, Africa and South America do not, and the EU has repeatedly discussed abolishing the practice without reaching a decision.
Fix it to one zone and let calendar software convert. If you fix it to UTC instead, it will shift by an hour for everyone observing daylight saving, twice a year.
Nothing you enter here leaves your browser
Timezone Converter & World Clock does its work in JavaScript running on your own device. The page loads once, and after that there is no upload step and no server involved — which matters here because exported data frequently contains customer records or transactions.
You can verify this rather than taking our word for it: load the page, disconnect from the internet, and the tool keeps working. Our privacy policy sets out what is and is not collected, and this guide explains why the distinction matters.