Epoch to human date and back. Seconds or milliseconds, detected automatically.
Unix time counts the seconds since 1 January 1970 UTC, a compact and timezone-free way to store a moment. Paste a 10-digit (seconds) or 13-digit (milliseconds) value to read it as a date in your local time and UTC, or pick a date to get its timestamp. Everything runs in your browser.
A Unix timestamp is the number of seconds that have elapsed since midnight UTC on 1 January 1970, a moment known as the "epoch". It is how computers store and exchange time internally, because a single number is unambiguous, easy to compare and free of timezone or formatting confusion. The tool above converts a timestamp to a human-readable date and back, which you need constantly when working with logs, databases and APIs.
Why systems love it. Storing time as one integer makes sorting, differences and comparisons trivial: later times are simply bigger numbers, and the gap between two events is a subtraction. Timezones and display formats are applied only when a human needs to read it, keeping the stored value clean and universal.
The 2038 problem. Older systems store the timestamp in a signed 32-bit integer, which overflows on 19 January 2038, after which it can wrap to a negative number and misread the date, a smaller echo of the Year 2000 bug. Modern systems use 64-bit integers, which push the limit hundreds of billions of years out, so it is a concern mainly for legacy hardware and embedded devices.