ISO 8601 to Unix timestamp

Counting seconds from an ISO date

Convert an ISO 8601 date-time with a timezone into Unix seconds. Use this direction when an API request, scheduled job or database column expects Unix seconds and you have a date-time with an explicit timezone. Supply a complete ISO form such as 2024-01-01T00:00:00Z or a numeric offset. A date without Z or an offset is rejected so the browser’s local timezone cannot silently change the answer.

The stated timezone offset is applied before counting seconds from 1970-01-01T00:00:00Z. The converter shifts the stated clock time by its offset to UTC, then counts from the 1970 epoch. Thus 2024-01-01T02:00:00+02:00 and 2024-01-01T00:00:00Z produce the same seconds. A fractional part of one to three digits is preserved; invalid calendar dates, missing seconds and leap seconds are reported instead of guessed. For a concrete check, the example input 2024-01-01T00:00:00.000Z produces 1704067200. Keep the original beside the result when comparing it with another application.

Two ways to express one instant

A Unix timestamp counts elapsed seconds from 1970-01-01T00:00:00Z. An ISO 8601 date-time names calendar fields and carries a timezone indicator, such as Z for UTC or an offset like +02:00. Both can identify one instant when the timezone is explicit. This converter keeps fractions to three decimal places, so millisecond precision is preserved in either direction. It is useful for API records, audit logs, scheduled jobs and debugging a timestamp copied from a database without relying on the computer’s local timezone.

Offsets, precision and calendar pitfalls

An explicit timezone is required for ISO input. Leap seconds and more than millisecond precision are outside this tool’s scope. An offset describes how clock time differs from UTC at that written instant; it is not the same as a named timezone with daylight-saving rules. The conversion applies the offset supplied in the input and displays UTC in ISO output. A date lacking a timezone is deliberately rejected because interpreting it as local or UTC could change the instant. Leap seconds such as 23:59:60 are outside the standard Date calculation used here. Fractions smaller than a millisecond are also outside scope, and very distant years are limited by the browser date range. Check the unit before pasting a timestamp: milliseconds are one thousand times larger than seconds.