Time Zone Converter & World Clock
Convert one time into every city that needs it, see the date rollovers, and find the hour that is not the middle of the night for somebody.
Nothing you type here is uploaded, stored or sent anywhere. It all runs in your browser.
Why the answer changes depending on the date you ask about
A time zone is not an offset. It is a set of rules about which offset applies when, and those rules change — not once, historically, but every year, in countries that are still making the decision. The gap between London and New York is five hours for most of the year, four hours for two weeks in March and one week in autumn, because the two places start and end daylight saving on different dates. A meeting booked in March for April can land an hour out for exactly that reason.
This page never stores an offset. It asks your browser what a zone's clock reads at the specific instant you asked about, and works backwards from that. That is why the offsets shown next to each city move when you change the date, and why a tool that shows you a fixed "UTC+4" next to a city is lying to you twice a year.
The three rollover traps
- The date, not just the time. A 9pm call in London is 6am tomorrow in Tokyo. Every converted time here carries its own date badge when it lands on a different day, because the number on its own is how people miss meetings.
- Southern hemisphere daylight saving runs the other way. Sydney gains an hour in October and loses it in April. For a few weeks each year the gap between London and Sydney is eleven hours, then nine, then ten.
- Some zones are not whole hours. India is UTC+5:30, Nepal is UTC+5:45, and the Chatham Islands are UTC+12:45. If a scheduling tool cannot show you a :45, it is rounding somebody's day.
Finding the hour that works
The strip is the part worth using. Reading three converted times tells you what one moment looks like elsewhere; reading the whole day tells you where the overlap actually is. Between London and Sydney there are roughly two usable hours a day, and they are early morning in one place and evening in the other — no amount of rearranging produces a third. Seeing that as a band of colour settles the argument faster than three emails do.
The shading follows the working hours you set, in each city's local time, not yours. That matters when the answer is "there is no good hour": then the question becomes whose evening you are spending, and that is a decision, not a calculation.
What the browser knows
All of this runs on Intl.DateTimeFormat, which has been in every browser for a decade and ships with the same IANA time zone database your operating system uses. It is kept current by the OS vendor, so it knows about last year's rule changes without this page being redeployed. Nothing is fetched and nothing is stored.
Questions people ask
Why does the offset next to a city change when I change the date?
Because it should. Daylight saving means most zones have two offsets, and the one that applies depends on the instant you asked about. This page computes the offset for that exact date and time rather than showing a single value that is wrong for a third of the year.
What do I type if my city is not in the list?
Any IANA time zone name — Europe/Berlin, America/Argentina/Buenos_Aires, UTC. The list holds a couple of hundred cities people actually schedule against, not every settlement on earth, and a zone name gives you the rest.
Does it handle the hour that daylight saving deletes?
Partly. On the spring-forward date, the hour between 2am and 3am does not exist in that zone, so there is no correct answer to "what instant is 02:30 here" — this page resolves it to 03:30 rather than pretending. On the autumn date, the repeated hour resolves to the first of the two. Both are edge cases you should schedule around rather than through.
Why are my colleagues in the same country shaded differently?
If they are in different zones, they are on different clocks. The United States has six, Australia has five in summer, and Brazil, Canada, Mexico and Russia all span several. Add each city separately rather than assuming the country.
Is anything I add here saved or sent anywhere?
No. The city list lives in the page for as long as the tab is open and goes nowhere. There is no backend, no account and no storage — reload the page and you are back to the defaults.
Related tools
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This page is here because free tools earn links from people who were never going to read a blog post. That is the whole trick, and it is most of what we do.