What is a duration?
A duration is an amount of time you add to or subtract from a base time. This calculator starts from a local date and time in a chosen time zone, then applies the same duration in both directions.
ISO 8601 examples
- PT45M means 45 minutes.
- P2DT6H means 2 days and 6 hours.
- P1DT2H3M4.005S means 1 day, 2 hours, 3 minutes, and 4.005 seconds.
How this calculator works
- Enter a base time in YYYY-MM-DD HH:mm:ss.SSS and choose the time zone you want to evaluate.
- Enter the duration either as ISO 8601 text or with the day, hour, minute, second, and millisecond fields. The tool keeps both inputs in sync and normalizes overflow.
- Enter positive durations only. Use the built-in add and subtract result cards to compare both directions.
- The result cards show the adjusted local time, the UTC ISO 8601 timestamp, and Unix timestamps in seconds and milliseconds. Offsets can change around daylight saving time transitions.