Duration Calculator
Add and subtract elapsed durations with exact milliseconds, total-hours formatting and a complete JSON report.
Your inputs stay in your browser.Add or subtract 1-100 durations. Hours 0-999999, minutes 0-59, seconds 0-59.999. Blank cells count as zero only in a populated row; empty rows are ignored. Drafts stay in memory only; refreshing clears them. Processing and exports stay local.
Enter values or try an example, then choose Calculate / Generate.
How to use Duration Calculator
Enter hours, minutes and seconds in each Add or Subtract row. Blank cells in a populated row mean zero; entirely blank rows are ignored. Add, duplicate or delete rows, choose 2-6 decimal places and Calculate. Export the full text summary or JSON with milliseconds stored as strings.
Worked example
1 hour 45 minutes plus 30 minutes is 2:15:00.000. 59.999 seconds plus 0.001 seconds is exactly one minute.
Rules and limits
1-100 rows. Hours 0-999999; minutes 0-59; seconds 0-59.999 with at most three fractional digits. Negative totals use one overall sign. A day means 24 hours. Secondary decimal totals round half away from zero and never replace exact milliseconds. This does not calculate clock times, DST, schedules or wages.
What should we improve next?
Help shape the next update to Duration calculator. Tell us what would make it better for you.
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