This guide covers How to Convert Between Time Zones | TimeFlow — what it means, how it works, and how to use it. The explanations below are followed by worked examples with real dates and real times, a set of frequently asked questions, and links to the tools that do the calculation for you: the time zone converter, the world clock, and the UTC converter. Where a number is given — an offset, a date, a count — it is computed from the IANA Time Zone Database for the date stated, not copied from a table that may be out of date.

Try the tool: Time Zone Converter — convert any time between any two cities, with the daylight saving rules for the date you choose.

Converting between time zones is a two-step calculation: convert the first city's time to UTC, then convert UTC to the second city's time. In practice that means one subtraction: the difference between the two offsets. If New York is UTC−05:00 and London is UTC+0, the difference is 5 hours, so 09:00 in New York is 14:00 in London.

The step people skip is the date. Offsets change with daylight saving, and the change dates differ by country, so the difference between two cities can change during the year. New York and London are 5 hours apart in winter and 4 hours apart for three weeks in March, when the United States has changed its clocks and Europe has not. Sydney and London are 11 hours apart in the northern winter and 9 hours apart in the northern summer. A conversion that is right in January can be wrong in July.

The method that never fails is to convert through UTC on the specific date. Take the time in city A, subtract A's offset on that date to get UTC, then add B's offset on that date. The time-zone converter on this site does exactly that, using the IANA database, so the result is right for the date you pick — including the awkward weeks when the two cities change their clocks on different days.

For a quick mental check, remember the offsets of the cities you deal with most, and remember whether they observe daylight saving. The offsets of the world's major cities are listed on the world clock pages on this site, with the winter and summer values side by side.

In practice

The method is to go through UTC. Convert the first city's time to UTC by subtracting its offset, then convert UTC to the second city's time by adding its offset. 3pm in New York in winter (UTC−05:00) is 20:00 UTC, and 20:00 UTC is 9am the next day in Tokyo (UTC+09:00). The two steps are the whole calculation — no tables, no lookup, just two additions.

The reason to go through UTC is that it is the fixed reference. Converting directly between two cities means subtracting one offset and adding another, which is the same calculation — but going through UTC makes it harder to get the sign wrong, and it makes the date change visible: when the result crosses midnight, the date changes, and you see it in the middle step. The time zone converter does the calculation for any two cities, with the daylight saving rules applied for the date you choose.

The practical shortcut is the offset difference. The gap between New York (UTC−05:00) and London (UTC+0) is five hours in winter, so you add five hours to New York time to get London time. The gap changes with daylight saving — it is four hours for a few weeks in March and October, because the two places change their clocks on different dates — so the shortcut is only safe if you know both offsets for the date in question.

The numbers: what 12:00 UTC looks like around the world

The table below shows the local time in eight major cities when it is 12:00 UTC on 15 January 2026. The spread is the whole point of time zones: the same moment is a morning in New York, midday in London, evening in Mumbai and night in Tokyo.

City Local time when it is 12:00 UTC (15 January 2026) UTC offset
New York 7:00 am UTC−05:00
London 12:00 pm UTC+00:00
Paris 1:00 pm UTC+01:00
Dubai 4:00 pm UTC+04:00
Mumbai 5:30 pm UTC+05:30
Tokyo 9:00 pm UTC+09:00
Sydney 11:00 pm UTC+11:00
Los Angeles 4:00 am UTC−08:00

Two things stand out. First, the range: from 04:00 in Los Angeles to 23:00 in Sydney, the same instant covers almost the whole day. Second, the half hour: Mumbai is at 17:30, not 17:00 or 18:00, because India uses a half-hour offset (UTC+05:30). If you convert a time for Mumbai by rounding to the nearest hour, you will be half an hour out. The UTC converter shows the offset and the local time for any city on any date, and the time zone converter converts between any two cities directly.

The offsets change during the year for the cities that observe daylight saving. The same eight cities in January and in July:

City Offset in January 2026 Offset in July 2026 Changes?
New York UTC−05:00 UTC−04:00 Yes — one hour
London UTC+00:00 UTC+01:00 Yes — one hour
Paris UTC+01:00 UTC+02:00 Yes — one hour
Dubai UTC+04:00 UTC+04:00 No
Mumbai UTC+05:30 UTC+05:30 No
Tokyo UTC+09:00 UTC+09:00 No
Sydney UTC+11:00 UTC+10:00 Yes — one hour
Los Angeles UTC−08:00 UTC−07:00 Yes — one hour

New York, London, Paris, Sydney and Los Angeles all change by one hour between January and July; Dubai, Mumbai and Tokyo do not, because they do not observe daylight saving. That is why a conversion done in January can be wrong in July — and why the UTC converter asks for the date.

Key facts

  • UTC never observes daylight saving. It is the fixed reference that every other time zone is measured against.
  • The world uses 38 different UTC offsets, from UTC−12:00 to UTC+14:00 — a span of 26 hours.
  • Nepal is on UTC+05:45, the only 45-minute offset in regular use. India is on UTC+05:30.
  • The Prime Meridian is at 0 degrees longitude, through Greenwich, London.
  • A time written in UTC means the same thing everywhere on Earth, in January and in July.

Frequently asked questions

How do I convert between two time zones?

Go through UTC: convert the first city's time to UTC by subtracting its offset, then convert UTC to the second city by adding its offset. The time zone converter does it for any two cities.

What is 3pm in New York in Tokyo?

In winter, 3pm New York (UTC−05:00) is 20:00 UTC, which is 5am the next day in Tokyo (UTC+09:00). In summer it is 4am, because New York is on EDT (UTC−04:00).

What is the time difference between London and Sydney?

Ten hours in the northern winter (London UTC+0, Sydney UTC+11:00) and nine hours in the northern summer (London UTC+01:00, Sydney UTC+10:00) — because the two cities change their clocks in opposite directions.

How do I convert a time and get the date right?

Watch for midnight: if the result is 24:00 or more, subtract 24 and add a day; if it is below 0:00, add 24 and subtract a day. The converter shows the date as well as the time.

What is the easiest way to convert time zones?

Use the time zone converter: pick the two cities and the date, and it gives the time in both, with the daylight saving rules applied.

What time is it in Tokyo when it is 12:00 UTC?

23:00 the same day — Tokyo is UTC+09:00 all year, so you add nine hours to 12:00 UTC. In New York it is 07:00 in winter (UTC−05:00) and 08:00 in summer (UTC−04:00). The UTC converter shows the time in any city for 12:00 UTC.

What is the time difference between London and Tokyo?

Nine hours in January 2026: London is UTC+00:00 and Tokyo is UTC+09:00. In July it is eight hours, because London moves to UTC+01:00 while Tokyo stays on UTC+09:00. The time zone converter gives the difference for any two cities and any date.

Related pages

Sources

  • IANA Time Zone Database, via Node.js Intl (Intl.DateTimeFormat with timeZone) — offsets, daylight saving dates and local times in this article were worked out from the IANA database, not typed from memory.
  • TimeFlow's own time-zone data (data/cities.ts, data/dst.ts), computed from the IANA database.
  • Time zone rules and offsets: the IANA Time Zone Database, as applied by this site's tools. Offsets and daylight saving dates on this page are computed from the database for the dates stated.
  • TimeFlow's time zone converter, world clock and UTC converter — the live tools behind the numbers on this page.
  • Time-zone and daylight saving rules are set by governments and can change. For flights, deadlines and meetings that cannot move, confirm the time with an official source.