Time zone difference calculator

Whether you're booking a flight, scheduling a call with a remote team, or trying to figure out what time to text your family abroad without waking them up, knowing the time difference between two cities is essential. The world is divided into 24 theoretical time zones, each spanning 15 degrees of longitude and representing one hour of difference from its neighbours. In practice, time zone boundaries follow political and administrative lines rather than strict geography, which is why neighbouring countries can sometimes be 30 or even 45 minutes apart.

All time zones are expressed as an offset from Coordinated Universal Time (UTC), the modern successor to Greenwich Mean Time (GMT). A location at UTC+5 is five hours ahead of UTC; a location at UTC-3 is three hours behind. The complication — and the source of most time zone confusion — is Daylight Saving Time (DST): many countries advance their clocks by one hour in summer, but they do so on different dates, temporarily shifting the differences between certain pairs of cities.

How to calculate the time zone difference

Once you know the UTC offsets for two cities, the calculation is simple subtraction. Here are the key variables:

• Origin city UTC offset : for example, New York in winter is UTC-5, meaning it is 5 hours behind UTC.
• Destination city UTC offset : for example, London in winter is UTC+0; Tokyo is UTC+9 year-round (Japan does not observe DST).
• Time difference : destination offset minus origin offset. New York (UTC-5) to London (UTC+0): 0 − (−5) = +5 hours. London is 5 hours ahead of New York in winter.

Formula: Difference = UTC_destination − UTC_origin. If the result is positive, the destination is ahead. If negative, the destination is behind. Key UTC offsets: Los Angeles UTC−8/−7, New York UTC−5/−4, London UTC+0/+1, Paris UTC+1/+2, Dubai UTC+4, Mumbai UTC+5:30, Bangkok UTC+7, Tokyo UTC+9, Sydney UTC+10/+11.

Example: New York to London and Los Angeles to Tokyo

Let's walk through two common scenarios. First: New York (UTC-5 in winter) to London (UTC+0 in winter). The difference is 0 − (−5) = +5 hours. When it is 9 AM in New York, it is 2 PM in London. In summer, New York moves to UTC-4 and London to UTC+1, so the difference remains 5 hours throughout the year in this particular case — though that isn't always true for other city pairs. Second scenario: Los Angeles (UTC-8 in winter) to Tokyo (UTC+9, no DST). The difference is 9 − (−8) = +17 hours. When it is Monday noon in Los Angeles, it is Tuesday 5 AM in Tokyo. This 17-hour gap means that scheduling a live meeting between these two cities will always inconvenience one side. For international meetings, the convention is to share times in UTC to avoid confusion — for example, "the call is at 14:00 UTC" rather than naming a city. Regarding jet lag: the rule of thumb is approximately one day of recovery per time zone crossed. A direct flight from New York to London crossing 5 time zones typically produces 4–5 days of disruption. Los Angeles to Tokyo, crossing 17 time zones, can require up to two weeks for full adjustment.

Frequently asked questions about time zones