Unix Timestamp Converter — Epoch ↔ Date (Seconds & ms)

One integer, one instant

A Unix timestamp counts the seconds elapsed since 1 January 1970 at 00:00:00 UTC — the epoch. One number, always increasing, trivially comparable and sortable, with no formatting or locale to argue about.

A timestamp has no time zone

This is the most important fact about the format, and almost every timestamp bug traces back to it.

The number is the same instant everywhere on Earth. A zone enters only at the moment it is displayed to a person. Two people looking at the same timestamp will correctly see different local times, and neither is wrong.

So when a stored time looks wrong by a whole number of hours, the timestamp is almost never the problem. Something applied a zone twice, or applied the wrong one, or parsed a local time as though it were UTC. The rule that avoids all of it: store the timestamp, and apply a zone exactly once, at the edge where a human reads it.

Seconds or milliseconds — count the digits

Unix tools, most databases and most languages work in seconds. JavaScript works in milliseconds. That mismatch is the usual source of confusion, and it is easy to diagnose.

For any current date, a seconds timestamp is 10 digits and a millisecond timestamp is 13. Nothing more subtle is needed.

Getting it wrong in one direction is loud: read a 13-digit millisecond value as seconds and you land tens of thousands of years in the future — around the year 56000 — which nobody mistakes for real data.

The other direction is quieter and therefore worse. Read a 10-digit seconds value as milliseconds and you land in January 1970, which looks like a plausible bug rather than an obvious one. Related and worth recognising: a date displayed as exactly 1 January 1970 at 00:00 almost always means the timestamp was zero or missing, not that anything happened in 1970.

The year 2038

A signed 32-bit seconds counter covers 1901 to 2038 and overflows on 19 January 2038. Systems still using one will need to move to 64-bit counters, which have no practical limit.

It is a real constraint on old software rather than an imminent crisis, and it is most likely to surface in embedded devices and long-lived database schemas rather than anything written recently.

Leap seconds

Unix time ignores them, so it is not an exact count of physical seconds since the epoch. They have been inserted irregularly, and none has been added since 2016.

This almost never matters, and it matters exactly once: if you are tempted to treat the difference between two timestamps as a precise physical interval for scientific timekeeping, it is not one.

Where you meet them

Log files, database columns, token expiry values, cache headers, and anywhere two events need comparing. The common task is reading one out of a log and finding out what it means, which is what this is for — paste it and get the local time, UTC and the ISO form together.

Everything runs in your browser. For the gap between two calendar dates rather than the meaning of a timestamp, see the date difference calculator.