ISO/RFC Date-Time Formatter

RFC-3339 is a profile of ISO-8601 for internet timestamps with UTC or offsets.

Format any date/time to ISO-8601, RFC-3339, RFC-1123, and more. DST and time-zones supported.

Local date & time Or use Unix seconds below. Timezone Unix (seconds) Milliseconds Use Z (UTC)

Timezone Offset DST Input (local) Input (UTC) ISO-8601 RFC-3339 RFC-1123 RFC-2822 Week date Ordinal date Unix (s) Unix (ms)

FAQ

ISO-8601 vs RFC-3339?
RFC-3339 is a stricter internet profile of ISO-8601 (e.g., 2025-10-29T12:34:56Z or with an offset).

Should I use Z or an offset?
Use Z for UTC APIs; use offsets when you must preserve a local wall time context.

What is RFC-1123?
An HTTP-friendly format (e.g., Wed, 29 Oct 2025 12:34:56 GMT).