Timestamp Converter

What an epoch timestamp is

A Unix timestamp counts seconds since 1 January 1970 at 00:00:00 UTC. It has no time zone: the same integer represents the same instant everywhere on Earth. Time zone only enters when you format it for a human. That property is exactly why timestamps are the right way to store and transmit instants, and why storing a local-time string is a recurring source of bugs.

Seconds or milliseconds

Unix tools, most databases and most backend languages use seconds. JavaScript's Date.now() uses milliseconds. Mixing them produces two unmistakable symptoms: a date in 1970 when milliseconds are read as seconds, or a date tens of thousands of years in the future when seconds are read as milliseconds. A present-day timestamp in seconds has 10 digits; in milliseconds it has 13. This tool detects the magnitude and tells you which it assumed.

The 2038 problem

A signed 32-bit integer holding seconds overflows on 19 January 2038, wrapping to a negative number and thus to 1901. Modern 64-bit systems are unaffected, but 32-bit embedded devices, older database columns and legacy file formats still carry the limit. It is worth checking any system that stores timestamps in a 32-bit field and is expected to outlive the next decade.

Leap seconds and UTC

Unix time deliberately ignores leap seconds: every day is exactly 86,400 seconds. When a leap second is inserted, the counter repeats a value rather than incrementing. This means Unix time is not a true count of elapsed SI seconds since the epoch, and durations computed across a leap second are off by one. For nearly all applications this is irrelevant, but it matters for precise interval measurement.

ISO 8601

When you need a human-readable instant that is still unambiguous, ISO 8601 with an explicit offset is the right format: 2026-08-12T03:41:00Z or with an offset such as +05:30. Avoid formats without an offset, and avoid ambiguous orderings where the day and month can be transposed.

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