Time & money

Duration calculator

Turn messy duration strings into seconds, clocks, and ISO-8601.

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Duration

What this tool does

Parse mode accepts English tokens, clock form, and ISO-8601 durations that use weeks, days, and the time designator. Add and subtract apply the span to a starting datetime. Years and months are rejected because they are not fixed numbers of seconds.

How to use it

Choose parse, add, or subtract.
Enter a duration such as 2h 15m or PT2H15M.
For add or subtract, enter a starting datetime.
Copy the JSON clock, ISO-8601, and human forms.

Supported input

A duration string, and optionally a starting datetime

Output

JSON with totalSeconds, clock, iso8601, and human text

Privacy

This tool processes files and text locally in your browser. Your content is not uploaded or stored by this site.

ConvertPass does not include your input in analytics, URLs, or error reports. Encoding: UTF-8 duration tokens / ISO-8601. Limit: 4 KB (4.0 KB).

Limitations

P1Y and P1M are refused. A year is not 31,536,000 seconds in every calendar.
Clock form 1:30 is minutes:seconds. Use 1:30:00 or 1h 30m for one hour thirty.
Leap seconds are not applied.

Example

Input

1h 30m

Output

{
  "totalSeconds": 5400,
  "clock": "01:30:00",
  "iso8601": "PT1H30M"
}

Troubleshooting

1:30 became ninety seconds: Two-part clock values are MM:SS. Write 1h 30m or 01:30:00 for ninety minutes.

FAQ

Does PT1H30M work?

Yes. ISO-8601 durations with D, W, H, M, and S are accepted. Years and months are not.

Can I add a duration to a timezone-aware meeting?

Add produces a UTC instant. Convert it with the time zone converter if you need a wall clock in another city.

Are decimal seconds allowed?

Yes in ISO form (PT1.5S) and in token form (1.5s).

Why refuse months?

February is not the same length as July. ConvertPass will not pick 30 days and hide the lie.

Related tools

Date difference
Count days and weekdays between two dates without a spreadsheet.
Time zone converter
Convert a meeting time across IANA zones without sending the date anywhere.
UNIX timestamp converter
Translate UNIX time and ISO-8601 without a timezone guessing game.

Related formats

JSON

Last reviewed 16 August 2026. Report a problem. Reports do not include your input.