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a count — it is computed from the IANA Time Zone Database for the date stated, not copied from a table that may be out of date.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

A Unix timestamp is a single number: the count of seconds since 00:00:00 UTC on 1 January 1970. The timestamp 1700000000 is 14 November 2023 at 22:13:20 UTC. The timestamp 0 is 1 January 1970 itself. Every second that passes, the number goes up by one.

Timestamps are how computers store time. A database stores a timestamp, not a string like '14 November 2023', because a number is unambiguous: it means the same moment everywhere on Earth, in every time zone, with no confusion about daylight saving or date formats. When your phone shows you a message time, it is converting a stored timestamp into your local time zone.

To convert a timestamp to a readable date, you need a time zone. The same timestamp is 14 November 2023 at 22:13 in London, 17:13 in New York, and 15 November at 07:13 in Tokyo. The timestamp itself has no time zone — it is a moment, and the local time is a presentation of that moment.

Timestamps are usually in seconds, but some systems use milliseconds (13 digits instead of 10) or microseconds. If a timestamp looks too long, divide by 1,000 — it is probably in milliseconds. And if you see a timestamp that is negative, it is a date before 1970: the system counts backwards from the epoch.

In practice

The timestamp is the same number whether you are in New York or Tokyo, and that is its power. A Unix timestamp does not have a time zone: it is a count of seconds since 1 January 1970 in UTC, and the same timestamp means the same instant everywhere on Earth. The time zone only appears when you convert it into a human date — and that conversion is where the bugs live, because two people converting the same timestamp in different zones will get different dates.

The commonest mistake is mixing seconds and milliseconds. JavaScript's Date object works in milliseconds, so Date.now() returns a 13-digit number; most other systems work in seconds, so they return a 10-digit number. If you pass a millisecond timestamp to a function expecting seconds, the date comes out thousands of years in the future. The fix is simple — divide by 1,000 — but it is the most common timestamp bug in the world.

Timestamps are also how computers store the past. A photograph's creation time, a file's modification time, a database record's creation time — all of them are timestamps, and all of them are in UTC. When your phone shows a photo as taken at 3pm, it is converting the stored UTC timestamp into your local time zone. Change your time zone and the photo's displayed time changes, but the timestamp — and the moment it records — does not.

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 is a Unix timestamp?

The number of seconds since 1 January 1970 (UTC) — the same as epoch time. It is the standard way computers record a moment.

Are Unix timestamps in seconds or milliseconds?

Usually seconds, but JavaScript's Date object works in milliseconds, so Date.now() returns a 13-digit number. Passing a millisecond timestamp to a function expecting seconds gives a date thousands of years in the future.

Does a Unix timestamp have a time zone?

No. It is a count of seconds since 1 January 1970 in UTC, and the same timestamp means the same instant everywhere. The time zone appears only when you convert it to a date.

How do I convert a Unix timestamp to a date?

Divide by 1,000 if it is in milliseconds, then convert from UTC using your offset. Most programming languages have a built-in function for it.

What happens to a timestamp when I change time zones?

Nothing. The timestamp records a moment, and the moment does not change — only the date shown changes, because your phone converts the timestamp into your new local time.

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.