This guide covers What Is UTC? | 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a count — it is computed from the IANA Time Zone Database for the date stated, not copied from a table that may be out of date.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.

UTC — Coordinated Universal Time — is the world's time standard. It is the time at 0 degrees longitude, the Prime Meridian at Greenwich, London, and every other time zone on Earth is defined as an offset from it: New York is UTC−05:00 in winter, Tokyo is UTC+09:00, Sydney is UTC+10:00 in winter and UTC+11:00 in summer.

UTC is not quite the same thing as GMT, though people use the two interchangeably. GMT is an older astronomical measure of mean solar time at Greenwich. UTC is an atomic time scale, kept by atomic clocks around the world and adjusted with leap seconds so it never drifts more than 0.9 seconds from the Earth's rotation. In everyday use the difference is zero — UTC and GMT show the same clock time — but UTC is the precise standard, and GMT is the historical name.

UTC never observes daylight saving. That is the whole point of it: it is the fixed reference that everything else is measured against. When London moves to British Summer Time, London is UTC+01:00 — UTC itself does not move. This is why flight times, server logs, weather data and international schedules are all recorded in UTC: it is the one clock that never jumps forward or back.

You use UTC more often than you think. When a website says an event starts at 14:00 UTC, it means 14:00 at Greenwich — 09:00 in New York in winter, 15:00 in Paris, 19:30 in Mumbai, 23:00 in Tokyo. Converting from UTC is the simplest time-zone calculation there is, because you only add or subtract your own offset.

In practice

UTC is the time that servers, aeroplanes and weather stations run on, and there is a good reason for that: it never changes. A timestamp in UTC means the same thing in January and in July, in London and in Tokyo. When you see a flight time, a log entry or a satellite pass quoted in UTC, you are seeing the one clock that every other clock is measured against.

The 'C' in UTC stands for 'Coordinated', and the name is a compromise — in English it would be CUT, in French TUC, so the two language communities agreed on UTC, which belongs to neither. It is a small detail, but it tells you something about how the standard was made: by international agreement, not by one country's decree, which is why the whole world accepts it.

Converting from UTC is the simplest time-zone calculation there is. Find your offset — New York is UTC−05:00 in winter, London is UTC+0, Mumbai is UTC+05:30, Tokyo is UTC+09:00 — and add it to the UTC time. 14:00 UTC is 09:00 in New York in winter, 14:00 in London, 19:30 in Mumbai and 23:00 in Tokyo. The UTC converter does this for any city, and the time zone converter converts between any two cities directly.

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

What does UTC stand for?

Coordinated Universal Time. The name is a compromise between the English CUT and the French TUC — UTC belongs to neither language.

Is UTC the same as GMT?

On your clock, yes: 14:00 UTC is 14:00 GMT. Underneath, UTC is an atomic time scale kept in step with the Earth's rotation by leap seconds, while GMT is an older solar measurement.

Does UTC observe daylight saving?

No, never. That is the point of it: UTC is the fixed reference that every other time zone is measured against. When London moves to BST, London is UTC+01:00 — UTC itself does not move.

What time is 14:00 UTC in New York?

09:00 in winter (UTC−05:00) and 10:00 in summer (UTC−04:00). In London it is 14:00 in winter and 15:00 in summer; in Tokyo it is 23:00.

Why is UTC used for flights and servers?

Because it never changes. A timestamp in UTC means the same thing in January and July, in London and Tokyo, so flight times, server logs and weather data are all recorded in UTC.

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.