OneTaskBy Tim King · Updated
Time Difference Calculator
Hours Ahead or Behind Between Two Cities, With UTC Offsets Table
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How the Time Difference Calculator works
This time difference calculator tells you how many hours one city is ahead of or behind another on the date you choose, with daylight saving applied for both. It also shows each city's UTC offset, the time in both right now and a table matching every hour in one city to the clock in the other.
The time difference between two places is the gap between their UTC offsets. The calculation is simple; the catch is that the offsets change during the year, and not on the same dates.
Time difference calculator formula
The formula is: difference = offset of the second city − offset of the first city, with both offsets taken on the same date. A positive answer means the second city is ahead. For example, on 15 January London is UTC+0 and Tokyo is UTC+9, so Tokyo is nine hours ahead. In July London moves to UTC+1 and Tokyo stays put, so the gap shrinks to eight hours. That is why the date matters.
How many hours ahead: a worked example with half hours
Not every offset is a whole hour. India is UTC+5:30 all year, so in another example, New York in summer (UTC−4) to Delhi is 9 hours 30 minutes. Nepal is UTC+5:45 and parts of Australia sit on half-hour offsets as well. The calculator works in minutes, so these come out exactly rather than rounded.
Common time differences from London
The table below shows how many hours each city is from London in January and in July 2026. A negative figure means that city is behind London.
Hours ahead of or behind London, January and July 2026
| City | January | July |
|---|---|---|
| New York | −5 | −5 |
| Chicago | −6 | −6 |
| Denver | −7 | −7 |
| Phoenix | −7 | −8 |
| Los Angeles | −8 | −8 |
| Anchorage | −9 | −9 |
| Honolulu | −10 | −11 |
| Mexico City | −6 | −7 |
| São Paulo | −3 | −4 |
| Buenos Aires | −3 | −4 |
| Reykjavik | 0 | −1 |
| Dublin | 0 | 0 |
| Paris | +1 | +1 |
| Berlin | +1 | +1 |
| Athens | +2 | +2 |
| Istanbul | +3 | +2 |
| Moscow | +3 | +2 |
| Dubai | +4 | +3 |
| Karachi | +5 | +4 |
| Delhi | +5:30 | +4:30 |
| Bangkok | +7 | +6 |
| Singapore | +8 | +7 |
| Hong Kong | +8 | +7 |
| Tokyo | +9 | +8 |
| Brisbane | +10 | +9 |
| Sydney | +11 | +9 |
| Auckland | +13 | +11 |
FAQ
Why does the time difference change during the year?
Because daylight saving moves some clocks and not others, and the two hemispheres move theirs at opposite ends of the year. London and Sydney are eleven hours apart in January and nine in July, with ten-hour weeks in between while only one of them is on summer time.
Is the time difference the same in both directions?
The size is the same, the sign flips. If Tokyo is nine hours ahead of London, London is nine hours behind Tokyo. The calculator states which city is ahead so you do not have to work out the direction from a plus or minus sign.
What date should I enter?
The date you care about, such as the day of a call or a flight. If you leave today's date in place you get the difference as it stands now, which may be an hour out a few weeks later if either city changes its clocks in between.
See also: all Time Zones and Travel tools, Calendars, Countdowns, Durations, Work and Contracts, Date Formats, Sun and Daylight.
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