Unix Timestamp Converter
Convert a Unix timestamp (seconds or milliseconds) to a readable date, or a date to a timestamp. Great for reading log files and API responses.
How to use it
Enter a timestamp, choose its unit (seconds/milliseconds), and convert to a date — or type a date and convert it to a timestamp. Results are shown in both UTC and your browser's local time zone.
Unix time and UTC
A Unix timestamp counts elapsed time from the Unix epoch at 1970-01-01 00:00:00 UTC. The number itself does not contain a time-zone name. Converting it to UTC produces the same instant everywhere, while the local display depends on the browser's current time-zone rules. When debugging an API, compare UTC values first so two developers in different regions do not mistake a display difference for a data difference.
Seconds versus milliseconds
Many backend systems and JWT claims use whole seconds, while JavaScript commonly uses milliseconds. Selecting the wrong unit shifts a date by a factor of one thousand: a current millisecond value interpreted as seconds lands far in the future, while a current second value interpreted as milliseconds lands near January 1970. Digit length is a useful clue but not a validation rule, especially for historical, negative, or deliberately truncated values. Confirm the producer's contract.
Convert dates without time-zone ambiguity
Prefer ISO 8601 input with an explicit Z or numeric offset, such as 2026-07-21T12:00:00Z or 2026-07-21T15:00:00+03:00. A date-time without an offset may be interpreted as local time, and date parsers do not all accept the same informal formats. If the source value represents a calendar date rather than an instant, decide the intended zone before converting it to Unix time.
Precision, rounding, and range
Converting milliseconds to seconds can discard sub-second precision. Decide whether the consuming system expects rounding or truncation and keep that choice consistent. This page reports integer seconds using the represented instant and also exposes milliseconds for comparison. Very large magnitudes can exceed the date range or exact integer precision supported by a browser, even when another language or database accepts them. Treat an invalid browser date as a range warning, not proof that every system rejects the value.
Common debugging uses
Timestamp conversion helps inspect JWT iat, nbf, and exp claims, API audit fields, webhook event times, database exports, and scheduler logs. Check the unit, UTC instant, local display, and expected ordering. For token-specific validation, use JWT Decoder; decoding a claim does not verify its signature or prove that the current clock satisfies the issuer's policy.
Daylight saving time and privacy
UTC has no daylight-saving transition, but a local representation can skip or repeat wall-clock times when regional rules change. Store instants in UTC and keep the intended zone separately when future local scheduling matters. All conversions on this page run locally, and entered timestamps or date strings are not sent to Cryonel. Clear copied production identifiers when you finish, and avoid placing sensitive values in shared URLs or logs.
Frequently Asked Questions
Is a Unix timestamp in seconds or milliseconds?
The Unix epoch is traditionally in seconds, while JavaScript's Date.now() returns milliseconds. A 10-digit value is usually seconds; a 13-digit value is usually milliseconds.
What is the Year 2038 problem?
On 32-bit signed systems, a second-based timestamp overflows on January 19, 2038. Modern 64-bit systems aren't affected.
What happens when a date has no time-zone offset?
It may be interpreted as local time. Use ISO 8601 with Z or an explicit numeric offset when the instant must be unambiguous.