What format is an ISO-8601 duration?

It starts with P, then optional date parts nYnMnWnD, then a T separator before optional time parts nHnMnS. For example P1Y2M10DT2H30M means 1 year, 2 months, 10 days, 2 hours, and 30 minutes.

Why does the M appear twice?

M before the T means months; M after the T means minutes. The T separator is what disambiguates them, which is why a time-only duration like 45 minutes is written PT45M.

How are years and months converted to seconds?

Years and months have no fixed length, so the tool uses Gregorian averages: a year is 365.2425 days and a month is one twelfth of that. Day, hour, minute, and second parts are exact.

Are fractional values allowed?

Yes. ISO-8601 permits a decimal fraction, such as PT1.5H for one and a half hours, using either a dot or a comma as the decimal separator. The parser accepts both.

Can it parse the week form like P2W?

Yes. A week component such as P2W is parsed as 14 days. The tool accepts weeks alongside the other fields rather than requiring them to be used alone.

ISO-8601 Duration Converter

What an ISO-8601 duration looks like

ISO-8601 represents a span of time as a string that begins with P for period. Date components come first as nY years, nM months, nW weeks, and nD days, followed by a T and the time components nH hours, nM minutes, and nS seconds. The same letter M means months before the T and minutes after it, which is the most common point of confusion. This tool parses the whole string and reports both totals and a per-component breakdown.

How it works

The parser matches the canonical grammar with a single regular expression, extracting each optional component and rejecting strings that do not fit, such as a trailing T with no time parts. It accepts decimal fractions written with a dot or a comma, so PT1,5H and PT1.5H are equivalent.

To compute a single total, the components are summed into seconds. Days, hours, minutes, and seconds are exact. Years and months have no fixed length, so the tool uses Gregorian mean values: a year is 365.2425 days and a month is one twelfth of a year. Weeks are exactly 7 days.

P1Y2M10DT2H30M  ->  about 37,090,800 seconds
PT45M           ->  2,700 seconds
P2W             ->  1,209,600 seconds

Example and notes

Use the component breakdown to verify intent before relying on the totals. If your duration contains only days and smaller units the totals are exact to the second. If it contains years or months, treat the seconds, minutes, and hours totals as averages, since a calendar year that includes a leap day is slightly longer than one that does not. For exact calendar arithmetic, add the duration to a specific start date rather than converting it to a fixed number of seconds.