Unix Timestamp

Unix seconds and milliseconds

Unix timestamps count seconds from 1970-01-01 00:00:00 UTC. Ten-digit values are usually seconds, while thirteen-digit values are usually milliseconds.

Current Unix seconds are usually ten digits. Current Unix milliseconds are usually thirteen digits. The same instant therefore appears as a much larger number in JavaScript, whereDate.now() returns milliseconds. A value with the wrong unit can land decades away from the intended date, so check the result rather than relying only on digit count.

Nothing is uploaded while you convert. JWT exp, nbf, andiat claims are normally Unix seconds, so you can inspect them with theJWT Decoder. If a claim looks like milliseconds, verify the issuer's contract before converting it.

UTC is the reference point

Unix time counts from 1970-01-01 00:00:00 UTC. It is not a local clock reading and it does not change when daylight saving rules change. This page displays the UTC result and a local-time result for your browser's time zone.

ISO 8601 input can include a Z suffix or an explicit offset. Read that offset before comparing a date with a timestamp. A local date with no offset can be ambiguous in other tools, so use an explicit UTC value when you are writing logs or an API contract. The guideUnix timestamps explained includes examples for both units.

Use timestamps as values, not explanations

A timestamp tells you when an event was represented, not why it happened or whether a request was authorized. Keep the original value when debugging, record the unit in your schema, and avoid converting back and forth repeatedly. For token claims, inspect the surrounding header and payload with the JWT Decoder before drawing a security conclusion.