Unix Timestamp Converter

Epoch time, explained

A Unix timestamp counts the number of seconds since midnight UTC on 1 January 1970, a moment called the epoch. It is a single number with no timezone attached, which makes it ideal for storing and comparing moments across systems. Converting goes both ways: a timestamp into a human date, and a date back into the number.

Seconds or milliseconds?

This trips people up constantly. Classic Unix time is in seconds, but JavaScript Date.now() and many APIs use milliseconds. If a date lands in 1970, you probably treated a seconds value as milliseconds or vice versa. The quick tell: a current seconds timestamp is 10 digits, a milliseconds one is 13.

Example

1700000000  (seconds)
= Tue, 14 Nov 2023 22:13:20 UTC

1700000000000  (milliseconds)
= same instant, 13 digits

Where you meet timestamps

They show up in log files, database columns, JWT iat and exp claims (see the JWT decoder), cookie expiries, and cache headers. Storing in UTC and formatting to the user timezone only at display time avoids a whole category of off-by-an-hour bugs around daylight saving changes.

FAQ

What is the year 2038 problem? A signed 32-bit second counter overflows in January 2038. Modern systems use 64-bit values, which pushes the limit billions of years out.

Does a timestamp include a timezone? No. It is always UTC-based. The timezone is applied only when you format it into a readable date.

Why is my converted time off by seconds? Unix time ignores leap seconds, so it can differ slightly from strict astronomical time, though for everyday use this is irrelevant.