Time Zone Calculator

Scheduling across time zones is where good plans fall apart — a call set for "3 PM" means little without knowing whose 3 PM. This calculator converts a date and time from one zone to another and shows the exact offset, and it can line up several cities at once.

Remote teams use it to find a meeting time that works across continents, travelers use it to know what time it is back home, and anyone coordinating a livestream or call uses it to avoid the classic off-by-an-hour mistake. It covers twelve major world zones and stays accurate through daylight saving changes by using your browser's built-in time-zone data.

Conversion is done through the browser's internationalisation support rather than by adding a stored offset. That matters because it means the calculation consults the actual rules for each zone on the date in question, including whether daylight saving was in effect at that moment.

An offset is a property of a moment in a place, not a property of the place. New York is five hours behind UTC in January and four in July, so converting with a fixed number is right for half the year and wrong for the other half. Selecting named zones — America/New_York rather than EST — is what allows the correct rule to be applied.

The difference between the two zones is reported alongside the converted time, which is usually the figure you actually want when scheduling something recurring.

Almost every assumption people hold about time zones is wrong somewhere. Not all offsets are whole hours. Not every country observes daylight saving, and those that do change on different dates — the European Union and the United States are misaligned for a few weeks twice a year, which is when transatlantic meetings quietly drift. Southern hemisphere countries shift in the opposite direction to northern ones. China spans a great deal of longitude on a single zone. Zone rules also change by legislation, sometimes at short notice.

For scheduling across zones, two habits avoid most problems: always state the zone explicitly rather than saying a bare time, and for recurring meetings expect the relative gap to move when either side changes clocks. Confirming against each participant's local time near the changeover weeks is worth the small effort.

One caution about this tool specifically. Because it relies on the zone database available in your browser, an out-of-date device may not know about a recent legislative change. For anything critical — a flight, a legal deadline, a market open — verify against an authoritative source rather than any converter.