tooloora

Time Zone Converter – with meeting planner

One moment in as many zones as you like, with UTC offset, abbreviation and day shift, honest about daylight saving edges, plus an hour grid that shows where working hours overlap. All local.

Runs locally — nothing is uploaded

Source time

1 zone available

Please fill in both date and time.

Target zones

No target zone yet. Search for a city above.

Zone data comes from your browser, no request leaves your device.

Convert one moment into many zones

Pick a date, a time and a source zone, add as many target zones as you like, and you see the same second everywhere, with UTC offset, zone abbreviation and a marker for the previous or next day. Below it, the meeting planner shows in an hour grid when everyone is inside working hours. Your browser does all the maths.

How does a time zone conversion actually work?

A moment in time is unambiguous, a local time is not. Conversion therefore always goes through the middle: local time plus the zone rule gives an absolute instant, and that instant plus the target zone's rule gives the local time there. There is no fixed hour gap between two cities. Berlin and New York are six hours apart, except for about two weeks a year when they are five or seven, because both regions switch on different weekends.

Where does the zone data come from?

From the IANA time zone database, often called tzdb or the Olson database, which ships with operating systems and browsers. It is the worldwide reference for civil time and gets updated several times a year whenever governments change their rules. The procedures for maintaining it are laid down in IETF RFC 6557. This tool reads the list straight from your browser via Intl.supportedValuesOf('timeZone'); current engines report more than 400 zones there. It implements no rules of its own: what your system knows, this tool knows, no more and no less.

What about daylight saving time and its edges?

This is where many converters are quietly wrong. In the EU, summer time starts under Directive 2000/84/EC on the last Sunday in March at 01:00 UTC and ends on the last Sunday in October. Two cases follow that ordinary arithmetic does not cover:

  • Skipped local time. On 29 March 2026 the clock in Europe/Berlin jumps from 02:00 to 03:00. The time 02:30 does not exist that day. This tool says so explicitly, names the size of the jump and continues with 03:30 following the usual convention, rather than silently picking some instant.
  • Doubled local time. On 25 October 2026 the clock goes back from 03:00 to 02:00. 02:30 happens twice, once at UTC+02:00 and a real hour later at UTC+01:00. The tool reports the ambiguity and lets you choose which occurrence you mean.

Those two hours a year are exactly what produces double-booked shifts, missed connections and alarms that ring at the wrong time. Naming them is more honest than smoothing them away.

How do I plan a meeting across time zones?

Use the hour grid. Each column is one hour in your source zone, each row is a selected zone, each cell shows the local time there. Cells that fall into working hours in that zone are highlighted; you can move the start and end of that window, the default is 9 to 17. Hours that are working time in every zone get an extra outline and can be adopted as the source time with one click. Berlin and New York, for instance, typically share only the 15:00 to 17:00 window in Berlin time.

If there is no shared hour at all, the tool says that too. Then the only options are to widen the working window deliberately or to split the meeting.

What do offset, abbreviation and day shift mean?

The UTC offset is the unambiguous value, such as UTC+02:00 or UTC+05:30. It is always right because it is computed from the zone rule for that exact instant. The abbreviation such as EDT or JST is convenient but not available everywhere: for many European zones the browser returns a GMT notation instead, which is why the offset always sits next to it. The day shift marks when the target zone is already on the next day or still on the previous one, which between Europe and East Asia is the rule rather than the exception.

Do my meeting times stay private?

Yes. The zone list, the offsets and the daylight saving rules all come from your own browser, no request leaves the page and it works offline. Your selected zones and the working window live only in this browser's local storage so that they are still there next time. Who is reachable when, and in which city, says a lot about working relationships, and that information does not leave your device here.

Frequently asked questions

What happens when a local time does not exist?

On the day clocks go forward, an hour is skipped. In Europe/Berlin on 29 March 2026, 02:30 never happens: the clock jumps from 02:00 straight to 03:00. Most converters silently pick some instant. This one says the local time does not exist, names the size of the jump and tells you which valid time it used instead, which is 03:30 following the usual convention of shifting forward by the gap.

And when a local time happens twice?

On the day clocks go back, an hour repeats. In Europe/Berlin on 25 October 2026, 02:30 occurs twice, once at UTC+02:00 and once at UTC+01:00, a full hour apart in real time. The tool flags the ambiguity and lets you pick the first or the second occurrence instead of guessing for you. This is exactly the case that makes flight and shift schedules go wrong.

Where does the list of time zones come from?

From your browser, through Intl.supportedValuesOf, which exposes the IANA time zone database that ships with every operating system and browser. That database is the reference implementation for civil time worldwide; the procedures for maintaining it are documented in IETF RFC 6557. Current engines list well over 400 zones, so a search field is more practical than a plain drop-down.

Why does the abbreviation sometimes say GMT+2 instead of CEST?

Because not every zone has an abbreviation in the underlying data. American zones carry EST and EDT, Japan carries JST, but for many European zones the browser returns a GMT notation instead. The tool shows whatever the engine provides and always adds the exact UTC offset, which is unambiguous even when a short name is not.

Is anything sent to a server?

No. The zone list, the offsets and the daylight saving rules all come from your own device, so nothing is transmitted and the tool works offline. Meeting times reveal who you work with and when you are available, so keeping them out of a third-party log is the better default. Your selected zones are kept in this browser's local storage only.

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