How time zone conversion works
Every time zone is an offset from Coordinated Universal Time (UTC), the world’s reference clock. To convert a time, the calculator first turns your local time into UTC, then adds the offset of each destination city.
Destination time = UTC + offset of the destination zone
The hard part is that offsets change. Many places move their clocks forward in spring and back in autumn for daylight saving time (DST), and they do it on different dates. This converter does not use a hand-made table: it reads the IANA time zone database built into your browser, the same data your phone and computer use, and applies the rules for the exact date you pick. So 9 AM in New York converts differently in July than in January, and the result is right for both.
Worked examples
Example 1: one meeting, six cities. A call is set for 9:00 AM on Wednesday 4 November 2026 in New York. US clocks went back on 1 November, so New York is on Eastern Standard Time (UTC−5), and 9:00 AM EST is 14:00 UTC.
| City | Local time | Offset |
|---|---|---|
| London | 2:00 PM Wednesday | GMT, UTC+0 |
| Dubai | 6:00 PM Wednesday | GST, UTC+4 |
| Karachi | 7:00 PM Wednesday | PKT, UTC+5 |
| New Delhi | 7:30 PM Wednesday | IST, UTC+5:30 |
| Tokyo | 11:00 PM Wednesday | JST, UTC+9 |
| Sydney | 1:00 AM Thursday | AEDT, UTC+11 (summer time) |
Sydney is already into the next day, which the converter marks as “next day”.
Example 2: the same call in summer and winter. A team in Karachi wants a daily 4:00 PM call with a colleague in Toronto. Pakistan has no daylight saving, so 4:00 PM PKT is always 11:00 UTC. In July, Toronto is on EDT (UTC−4), so the call is at 7:00 AM. In January, Toronto is on EST (UTC−5), so the same call is at 6:00 AM. The gap between the cities changes from 9 to 10 hours even though nobody in Karachi touched a clock.
Example 3: the weeks when the gap shrinks. The US moves its clocks forward on the second Sunday in March, but the UK and EU wait until the last Sunday. On Monday 16 March 2026, New York is already on EDT (UTC−4) while London is still on GMT. So 10:00 AM in New York is 2:00 PM in London, not the usual 3:00 PM. The same thing happens for one week in late October and early November. These weeks cause many missed meetings.
Common time zones
| Region | Standard time | Daylight time |
|---|---|---|
| US Eastern (New York, Toronto) | EST, UTC−5 | EDT, UTC−4 |
| US Central (Chicago) | CST, UTC−6 | CDT, UTC−5 |
| US Mountain (Denver) | MST, UTC−7 | MDT, UTC−6 (Arizona stays on MST) |
| US Pacific (Los Angeles, Vancouver) | PST, UTC−8 | PDT, UTC−7 |
| UK and Ireland | GMT, UTC+0 | BST / IST, UTC+1 |
| Central Europe (Paris, Berlin) | CET, UTC+1 | CEST, UTC+2 |
| Gulf (Dubai, Muscat) | GST, UTC+4 | none |
| Pakistan | PKT, UTC+5 | none |
| India and Sri Lanka | IST / SLST, UTC+5:30 | none |
| China, Singapore, Philippines | UTC+8 | none |
| Japan and Korea | JST / KST, UTC+9 | none |
| Sydney and Melbourne | AEST, UTC+10 | AEDT, UTC+11 |
Abbreviations are not unique: CST can mean US Central or China Standard Time, IST can mean India, Ireland or Israel, and BST means British Summer Time or Bangladesh Standard Time. When you schedule something, name the city or the UTC offset instead.
When the clocks change
| Place | Clocks go forward | Clocks go back |
|---|---|---|
| United States and most of Canada | 2nd Sunday in March, 2:00 AM | 1st Sunday in November, 2:00 AM |
| UK and European Union | Last Sunday in March, 01:00 UTC | Last Sunday in October, 01:00 UTC |
| South-east Australia | 1st Sunday in October | 1st Sunday in April |
| New Zealand | Last Sunday in September | 1st Sunday in April |
Most of Asia, Africa and the Middle East do not use daylight saving time, including Pakistan, India, China, Japan, the UAE and Saudi Arabia. Mexico ended it for most of the country in 2022. In the southern hemisphere summer falls in December and January, so Sydney’s clocks move the opposite way to London’s.
On the morning the clocks go forward, an hour is skipped. In the US, 2:30 AM does not exist on that Sunday, so the converter moves it to 3:30 AM and shows a warning. When the clocks go back, an hour repeats; the converter uses the first one.
Tips for scheduling across time zones
- Send times in the reader’s zone, or in UTC. “3 PM London / 10 AM New York” leaves no room for doubt.
- Use the hour-by-hour planner. Bold times fall between 9 AM and 6 PM local time, so the rows with the most bold cells are the friendliest meeting slots.
- Watch the change weeks in March, October and November. Recurring meetings between the US and Europe shift by an hour for a week or two.
- Share the link. The address updates as you change cities or times, so you can send someone the exact conversion.
Related tools
To add hours to a time or work out a duration, use the time calculator. For shift lengths across midnight, try the hours calculator, and to count the days until an event, the date calculator.