🌍 Time Zone Calculator
Convert a time between any two cities, with daylight saving handled by your browser's own time zone database so the answer stays right across the spring and autumn transitions.
Converting times between cities without getting caught out
A time zone is an offset from Coordinated Universal Time, and most of the difficulty in converting between them comes from the fact that the offsets move. Daylight saving changes the gap between two cities several times a year, and the two cities rarely change on the same weekend.
The transition weeks
Europe and North America both observe daylight saving and both do it on different dates. Europe switches on the last Sunday of March and October; the United States switches on the second Sunday of March and the first Sunday of November. That leaves two windows each year when the usual gap is wrong:
| Period | Difference |
|---|---|
| Most of the year | 5 hours |
| Second Sunday of March to last Sunday of March | 4 hours |
| Last Sunday of October to first Sunday of November | 6 hours |
For three weeks in March the gap is four hours rather than five, and for one week in late autumn it is six. Every year a lot of international meetings are missed in those windows, because people apply the usual offset from memory.
This calculator uses your browser's own time zone database, which knows the historical and scheduled rules, so it applies the correct offset for the date you enter rather than for today. That is the whole reason to use a calculator rather than arithmetic.
The southern hemisphere runs the other way
Australia and New Zealand observe daylight saving in their summer, which is the northern winter. So the gap between London and Sydney swings from 9 hours to 11 across the year, a two-hour variation, and for short periods it passes through 10. Scheduling a recurring call between Europe and Australia means the local time drifts twice a year in both places, usually in opposite directions.
Not every offset is a whole hour
| Place | Offset |
|---|---|
| India | UTC+5:30 |
| Iran | UTC+3:30 |
| Afghanistan | UTC+4:30 |
| Myanmar | UTC+6:30 |
| Nepal | UTC+5:45 |
| Chatham Islands | UTC+12:45 |
| Newfoundland | UTC−3:30 |
Nepal's 45-minute offset exists because it was set relative to a mountain peak rather than to a meridian. India uses a single zone across a country wide enough for two, which means the sun rises almost two hours earlier in the east than in the west on the same clock.
Places that do not change their clocks
Most of Asia, Africa and South America do not observe daylight saving at all, along with Arizona and Hawaii in the United States and Queensland in Australia. Russia abolished it in 2014 and Mexico largely abolished it in 2022. The EU voted to end the practice in 2019 and has not implemented it, which is why the March and October switches continue.
Practical advice for scheduling
- Agree in UTC for anything technical. It never changes and has no ambiguity.
- Name the city, not the abbreviation. CST is Central Standard Time in the US, China Standard Time and Cuba Standard Time. BST is British Summer Time and Bangladesh Standard Time.
- Send calendar invitations rather than times in text. A calendar entry carries the zone; a line in an email carries an assumption.
- Check the week either side of a transition for any recurring meeting across continents.
A worked example
A 14:00 meeting in Madrid on 15 July. Madrid is on CEST, UTC+2, so the moment is 12:00 UTC, which is 08:00 in New York on EDT. On 15 January the same 14:00 Madrid time is CET, UTC+1, so 13:00 UTC and still 08:00 in New York, now on EST. The gap holds at six hours both times, but on 20 March it would be five, because the US has switched and Europe has not.
The natural follow-ups are the time calculator, for what this figure feeds into, and the date calculator, for the closely related case.
Frequently Asked Questions (FAQs)
Why does the time difference between cities change?
Because daylight saving starts and ends on different dates in different countries. Europe switches on the last Sunday of March and October, the US on the second Sunday of March and first Sunday of November, leaving several weeks each year when the usual gap is wrong by an hour.
What is UTC and how does it differ from GMT?
UTC is the modern time standard, maintained by atomic clocks. GMT is a time zone, used by the UK in winter, which happens to equal UTC+0. In casual use they are interchangeable; in technical contexts UTC is the correct reference because it never shifts.
Which countries do not use daylight saving?
Most of Asia, Africa and South America, plus Arizona, Hawaii, Queensland and Russia. Mexico largely abolished it in 2022. The EU voted to end it in 2019 but has not implemented the change, so European clocks still move twice a year.
Why do some time zones have 30 or 45 minute offsets?
Historical and political choices rather than astronomical ones. India uses UTC+5:30 as a single zone for a country two hours wide, and Nepal's UTC+5:45 was set relative to a mountain rather than a meridian. Several scheduling systems still handle these badly.
How should I schedule a meeting across time zones?
Send a calendar invitation rather than a time written in an email, and agree in UTC for anything technical. Name cities rather than abbreviations, since CST and BST each mean more than one thing. Check the weeks around daylight saving transitions.
Does this calculator handle daylight saving automatically?
Yes. It uses your browser's time zone database, which contains the rules for each zone, and applies the offset in force on the date you enter rather than today's. That is why the answer is correct in the transition weeks.