Time difference calculator
Pick any two cities or time zones and a date to see the exact time difference, with daylight saving time included. Defaults to New York and India.
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How a time difference is worked out
Every time zone is defined as an offset from Coordinated Universal Time (UTC). New York in winter is UTC−5, London in winter is UTC+0 and India is always UTC+5:30. The time difference between two places is simply the difference between their two offsets on the day in question: New York to London is 0 − (−5) = 5 hours, and New York to India is 5.5 − (−5) = 10.5 hours. The place with the larger offset is ahead, which means its clock shows a later time. When it is noon in New York, it is 5:00 PM in London and 10:30 PM in India.
The calculator above does exactly this, using the time zone rules built into your browser (the IANA time zone database). It reads each place’s offset on the date you pick, subtracts, and writes the answer as “B is N hours ahead of (or behind) A”. It also shows the current local time in both places, so you can see the result against a real clock, and the exact offset for the chosen date, for example UTC−4 for New York on a July day.
Why the difference changes in spring and autumn
A time difference is not a fixed property of two cities, because many places change their clocks and others do not. When the United States moves to daylight saving time in March, New York goes from UTC−5 to UTC−4. India does not change, so India is suddenly one hour closer: 10.5 hours becomes 9.5 hours. Nothing about India has moved. The whole change comes from the clock that jumped.
The subtler case is two places that both change clocks, but on different days. The United States changes on the second Sunday of March and the first Sunday of November. The United Kingdom changes on the last Sunday of March and the last Sunday of October. Between the two dates one side is on summer time and the other is not, and the gap between them is one hour different from normal. In 2027 that happens from 14 to 28 March and from 31 October to 7 November. The calculator picks this up automatically, and so does the note under the result, which names every clock change between today and the date you chose.
Worked examples
New York and London are five hours apart for most of the year. When it is 9:00 AM in New York, it is 2:00 PM in London. In the weeks when only one of them has changed its clocks, the gap is four hours, and 9:00 AM in New York is 1:00 PM in London. A recurring weekly call that you have set up in London time therefore appears one hour earlier on the New York calendar for those two weeks in March 2027, and one week in the autumn.
India and California are 13.5 hours apart in winter and 12.5 hours apart in summer. At 9:00 AM in San Francisco it is 10:30 PM the same day in India during winter, and 9:30 PM in summer. The half hour in the answer comes from India’s UTC+5:30 offset, and it is why people who think of India as “12 or 13 hours ahead” often get the minutes wrong.
| Pair (first is ahead) | January 2027 | July 2027 | Other weeks in 2027 |
|---|---|---|---|
| London – New York | 5 h | 5 h | 4 h from 14 to 28 March and 31 October to 7 November |
| India – New York | 10 h 30 min | 9 h 30 min | Changes on 14 March and 7 November |
| India – California | 13 h 30 min | 12 h 30 min | Changes on 14 March and 7 November |
| India – London | 5 h 30 min | 4 h 30 min | Changes on 28 March and 31 October |
| Tokyo – New York | 14 h | 13 h | Changes on 14 March and 7 November |
| Dubai – London | 4 h | 3 h | Changes on 28 March and 31 October |
| Sydney – London | 11 h | 9 h | 10 h from 28 March to 3 April and from 3 to 30 October |
Southern hemisphere and places with no clock changes
Daylight saving time works in opposite seasons in the northern and southern hemispheres. Sydney is on daylight time from the first Sunday of October to the first Sunday of April, which is summer in Australia, so the Sydney to London gap swings from 11 hours in January to 9 hours in July, with 10 hours in the transitional weeks. Many countries do not change their clocks at all: India, Japan, Singapore, China, the United Arab Emirates and most of Africa and South-East Asia keep one offset all year, and so do Hawaii and most of Arizona in the United States. For those places, every change in the time difference comes from the other end.
If you plan a meeting several months ahead, do not assume that today’s difference will still apply. Use the date field above for the actual date of the meeting. For the most common pairs we also keep dedicated pages with the full year’s dates and a 24-hour conversion table.
Time difference pages for popular pairs
Each page lists the current difference for every relevant time zone, the exact clock-change dates for 2026 and 2027, the weeks when the gap shifts, and an hour-by-hour conversion table with the shared working hours highlighted. For a single time rather than a gap, see the full list of converters, or the 24-hour clock converter if you only need to translate between 12-hour and 24-hour notation.
Quick answers
How do I calculate the time difference between two cities?
Find each city’s UTC offset on the date you care about and subtract. New York in winter is UTC−5 and London is UTC+0, so London is 5 hours ahead. The calculator above does this for any two IANA time zones and any date, including daylight saving time.
Why is the time difference between New York and London sometimes 4 hours?
The US and the UK change their clocks on different dates. In the weeks between the two changes (14 to 28 March 2027 and 31 October to 7 November 2027), one side is on summer time and the other is not, so the gap is 4 hours instead of 5.
What is the time difference between India and California?
13.5 hours while California is on standard time (PST) and 12.5 hours while it is on daylight time (PDT). India is always ahead because it does not change its clocks.
Does the calculator take daylight saving time into account?
Yes. It uses the time zone rules in your browser to find each place’s offset on the date you pick, and it lists any clock changes between today and that date.
What does “ahead” and “behind” mean in a time difference?
A place that is ahead has a later clock time. If London is 5 hours ahead of New York, it is 5:00 PM in London when it is noon in New York. A place that is behind has an earlier clock time.