Duration Calculator: Add & Subtract Hours, Minutes, Seconds
Add and subtract explicit durations beyond 24 hours, preserving signed totals without confusing elapsed time with wall-clock dates.
Enabling local controls…
1. Enter durations
Data is calculated in page memory. This adds duration spans, not wall-clock times, calendar months, dates or wages.
Up to 64 KiB and 1,000 lines. Strict H…:MM:SS or S…s, up to 3 decimal places. Hours: 12 digits; seconds: 16 digits. Minutes/seconds: 00–59. Errors and blank lines are rejected; one final newline is allowed. Hours do not wrap at 24; BigInt preserves milliseconds.
2. Result
Paste durations or load a sample, then calculate.
How to use this tool
Enter one signed duration per line using the displayed grammar, calculate, then copy the total duration and total seconds.
When not to use it
Hours do not wrap at midnight. No months, calendar-day arithmetic, time-zone or daylight-saving conversion, payroll or rounding policies.
Read the guide →