Date Format Converter

By digit count. 10-or-11-digit pure-integer input is treated as seconds (Unix timestamps are 10 digits through year 2286); 13-plus digits is milliseconds.

ISO 8601 requires an offset on local-time strings (+09:00, -05:00) so the instant is unambiguous. The UTC variant ends in Z and the offset is implicit.

The format HTTP defines for the Date, Expires, Last-Modified, Set-Cookie (Expires=) headers — Mon, 02 Jun 2026 15:04:05 GMT. Always UTC.

Locale (date / time string) and the local-timezone offset depend on your browser settings. The Unix epoch and ISO UTC values are the same everywhere.

When a millisecond timestamp is small enough to look like a second one. Any pure integer of eleven digits or fewer is read as seconds, so 1000000000 is taken as September 2001 rather than as the twelfth of January 1970, which is what it means in milliseconds. That only bites on timestamps from the first weeks of the epoch, but it is silent when it does. Current-era values are unambiguous: ten digits is seconds, thirteen is milliseconds, and anything eleven or twelve digits long read as seconds lands thousands of years in the future.

It is the last second a signed 32-bit integer can hold, and it falls on 19 January 2038 at 03:14:07 UTC. Systems still storing Unix time in a 32-bit signed field wrap to a negative number one second later and read it as December 1901 — the same shape of bug as Y2K, still present in older embedded firmware, some file formats and legacy database columns. Converting a date near that boundary here is a quick way to see whether a value your system produced has already wrapped.