How to Convert Time Zones: A Practical World Clock Guide
September 26, 2026
To convert a time between time zones, first convert it to UTC by subtracting the source zone's UTC offset, then add the destination zone's offset. For example, 9:00 in New York in summer (UTC−4) is 13:00 UTC, which is 14:00 in London (UTC+1) and 22:00 in Tokyo (UTC+9). The most common error is using the wrong offset because one of the places is — or isn't — on daylight saving time on that date.
What is the formula for converting between time zones?
Destination time = source time − source UTC offset + destination UTC offset. Offsets are written relative to Coordinated Universal Time (UTC): New York is UTC−5 in winter, Berlin is UTC+1 in winter, and so on. Subtracting a negative offset means adding: 9:00 in New York in winter (UTC−5) is 9:00 + 5 = 14:00 UTC, and 14:00 UTC is 15:00 in Berlin (UTC+1). If the result goes past midnight, move the date forward a day; if it goes below 00:00, move it back a day.
How do you convert time zones step by step?
Step 1: find the UTC offset of the source location on the exact date, including daylight saving time if it applies. Step 2: convert the source time to UTC. Step 3: find the destination's offset on that date. Step 4: apply it and check whether the date changed. Worked example: a call at 16:30 in Paris on 10 July. Paris is on summer time (UTC+2), so it is 14:30 UTC. Mumbai is UTC+5:30 all year, giving 20:00 the same day; Los Angeles is on daylight time (UTC−7), giving 07:30 the same day; Sydney is on standard time in July (UTC+10), giving 00:30 on 11 July. To skip the arithmetic, the free world clock and time zone map shows the current local time in cities around the world side by side.
What are the UTC offsets of major cities?
The table shows standard-time and daylight-saving offsets for widely used zones. Several places don't observe daylight saving time at all, and some use half-hour or even 45-minute offsets, which is why you can't assume every zone is a whole number of hours away.
| City | Standard time | Daylight saving time | Notes |
|---|---|---|---|
| Los Angeles | UTC−8 | UTC−7 | US rules |
| New York | UTC−5 | UTC−4 | US rules |
| London | UTC+0 | UTC+1 | UK/EU rules |
| Paris / Berlin | UTC+1 | UTC+2 | EU rules |
| Jerusalem / Tel Aviv | UTC+2 | UTC+3 | Israel's own DST dates |
| Dubai | UTC+4 | — | No DST |
| Mumbai / New Delhi | UTC+5:30 | — | No DST; one zone for all of India |
| Kathmandu | UTC+5:45 | — | No DST |
| Beijing / Shanghai | UTC+8 | — | No DST; one zone for all of China |
| Tokyo | UTC+9 | — | No DST |
| Sydney | UTC+10 | UTC+11 | DST runs roughly October to April |
| Auckland | UTC+12 | UTC+13 | DST runs roughly September to April |
How does daylight saving time affect time zone conversion?
Daylight saving time moves a zone's offset forward by one hour for part of the year, and different regions switch on different dates. The United States and Canada move clocks forward on the second Sunday in March and back on the first Sunday in November. The UK and EU switch on the last Sunday in March and the last Sunday in October. That mismatch creates a few weeks each spring and autumn when New York is four hours behind London instead of the usual five. Southern-hemisphere zones such as Sydney observe daylight saving time during their summer, so the gap between Sydney and London can change by two hours over the year. Many places — including Japan, China, India, most of Arizona and Queensland — don't use daylight saving time at all.
Why are time zone abbreviations like EST or IST confusing?
Because the same abbreviation can mean different zones, and people often use the winter name all year. IST can mean India Standard Time (UTC+5:30), Israel Standard Time (UTC+2) or Irish Standard Time (UTC+1); CST can mean US Central Standard Time (UTC−6) or China Standard Time (UTC+8). "EST" in July is usually meant as Eastern Daylight Time (UTC−4). To avoid mistakes, write the UTC offset or a city name — or, in software, an IANA time zone identifier such as America/New_York or Asia/Jerusalem, which also carries the correct daylight saving rules.
What is the difference between UTC and GMT?
UTC (Coordinated Universal Time) is the international time standard that time zones are defined against; it is kept by atomic clocks and never changes for daylight saving. GMT (Greenwich Mean Time) is historically the mean solar time at Greenwich, and today it's also the name of the time zone the UK uses in winter. For scheduling, GMT and UTC show the same clock time. The difference that matters in practice is that London is not on GMT in summer — it's on British Summer Time, UTC+1.
How do you schedule a meeting across several time zones?
Pick the date first, because offsets depend on it. Convert everyone's working hours to UTC and look for the overlap; between Europe and the US West Coast, for example, ordinary 9-to-5 office hours barely overlap or don't overlap at all, so someone has to start early or stay late. Send the invitation from a calendar app rather than typing times in an email, so each attendee sees it in their own zone. If you do write a time in text, include the zone or offset and, for calls that cross midnight somewhere, the date for each side. Double-check meetings booked during the weeks when the US and Europe change clocks on different dates.