Every conversion is one subtraction. Each zone is defined by its offset from Coordinated Universal Time, so the gap between two cities is the difference between their two offsets — and the time in the second city is the time in the first plus that gap. Add a city above and it appears alongside yours with the difference already worked out.
Two things make it go wrong by hand. Offsets are not fixed: a city on summer time sits an hour off its winter offset, and countries switch on different dates, so for a few weeks each spring and autumn the usual gap is simply not the usual gap. And not every offset is a whole hour — India runs at UTC+5:30, Nepal at UTC+5:45, parts of Australia at UTC+9:30. The daylight saving dates for every country are listed separately.
How to convert a time by hand
Find each city's current UTC offset — the table below has the common ones, and it changes when a country goes on or off summer time.
Subtract the first offset from the second. That signed number is the gap.
Add the gap to the original time. If the result passes 24:00 or drops below 00:00, the date moves with it.
Say the result with its date. “02:00” is not an answer; “02:00 on Tuesday” is.
a whole-hour gap
09:00 in New York is 14:00 in Berlin.
Berlin is +5 hours from New York today.
a half-hour zone
09:00 in London is 14:30 in Mumbai.
Mumbai is +5 hours 30 minutes from London today — not a whole number of hours, so the minutes move too.
a gap that crosses midnight
17:00 in London is 04:00 in Sydney, the next day.
Sydney is +11 hours from London today — wide enough that the calendar date changes.
The conversions people ask for most
Worked out for right now, with daylight saving already applied where it is in force. The 9:00 column is there because it is the hour most people are converting — the start of someone's working day.
Offsets shown for the moment this page was built. The clocks above are live.
The weeks when the usual gap is wrong
Two cities that both observe daylight saving are not always the same distance apart, because they rarely change on the same Sunday. Between the two dates the gap is an hour off — and in the Southern Hemisphere the clocks move the opposite way, so the gap to Sydney or São Paulo swings by two hours over the year. These are the windows for 2026, read from the time zone database rather than typed in.
Most conversions that go wrong go wrong here rather than in the arithmetic. IST is India (UTC+05:30), Israel (UTC+02:00) and Ireland (UTC+01:00) — a spread of four and a half hours. CST is the central United States (UTC−06:00), all of China (UTC+08:00) and Cuba (UTC−05:00). BST is British Summer Time (UTC+01:00) and Bangladesh Standard Time (UTC+06:00). Six abbreviations in common use mean more than one thing, so where it matters, write the offset instead of the letters — the full list of abbreviations has the rest.
The second trap is the date. Converting across nine hours or more usually lands on a different day, which is why every row above says so when it does — 17:00 in London is 02:00 in Sydney, but tomorrow.
Common questions
How do I convert a time from one time zone to another?
Take the difference between the two UTC offsets and add it to the original time. If New York is UTC−4 and Berlin is UTC+2, Berlin is six hours ahead, so 09:00 in New York is 15:00 in Berlin. The converter does this for every city you add at once, and applies daylight saving for the date in question.
Does the converter handle daylight saving time?
Yes. Offsets come from the IANA time zone database through the browser, so a city that is on summer time reports its summer offset. This matters most in the weeks when one country has changed and the other has not, which is when manual conversion usually goes wrong.
What about time zones that are not a whole number of hours?
They are handled the same way. India is UTC+5:30, Nepal UTC+5:45, and parts of Australia UTC+9:30. Converting by whole hours alone gives the wrong answer for roughly a fifth of the world.
Why does my converted time land on a different day?
Because the gap is wider than the hours left in the day. London to Sydney is nine hours, so 17:00 on a London Monday is 02:00 on a Sydney Tuesday. Anything across nine hours or more will usually cross midnight in one direction or the other, which is why a converted time is only complete with its date attached.
What does IST convert to?
It depends which IST. India Standard Time is UTC+05:30, Israel Standard Time is UTC+02:00 and Irish Standard Time is UTC+01:00 — up to four and a half hours apart. CST and BST are ambiguous in the same way. Where the answer matters, use the UTC offset rather than the letters.
Is the difference between two cities always the same?
No. Countries move on and off daylight saving on different dates, so the usual gap is wrong for a few weeks each spring and autumn. London and New York are five hours apart for most of the year and four for about three weeks in March and one week in autumn: the US moves on the second Sunday in March and the first Sunday in November, the UK and EU on the last Sundays of March and October, and in both mismatch windows the gap shrinks by an hour.
What is the difference between UTC and GMT?
For converting times, none: both mean the zero point the offsets are measured from, and no city is ever "on GMT" in summer. UTC is the modern standard kept by atomic clocks; GMT is the older name tied to the Greenwich meridian. The UK itself is on GMT (UTC+0) in winter and BST (UTC+1) in summer.
How do I convert one time for three or more cities at once?
Convert each city from the same starting point rather than chaining them, or the day-boundary shifts compound. The meeting planner does this for any number of cities on one grid, colouring each hour by whether it falls in office hours, so the overlap is visible instead of calculated.
Why is 12:00 EST not always 17:00 GMT?
Because for most of the year New York is on EDT, not EST. EST is UTC−5, EDT is UTC−4, and people write "EST" for both. 12:00 EST is 17:00 UTC; 12:00 EDT is 16:00 UTC — and the UK is usually on BST (UTC+1) at the same time, which moves the London clock again. Use the city name and the date instead of the letters.
How do I read "UTC−4" or "UTC+5:30"?
As hours (and minutes) to add to UTC. UTC−4 means the local clock is four hours behind UTC: at 12:00 UTC it is 08:00 there. UTC+5:30 means five and a half hours ahead: 12:00 UTC is 17:30. The sign always reads from UTC to the city, never the other way.
Planning a call rather than converting a single time? The meeting planner shows the overlapping working hours for every city at once.