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Duration Calculator
Add and subtract durations, or sum daily timecards (in/out times with breaks) to a running total.
What this tool does
Two calculators in one: Add durations sums a list of time spans (each row can be added or subtracted), and Sum timecard adds up daily shifts based on clock-in / clock-out times and an optional break in minutes. The total is shown in HH:MM:SS, in whole hours, minutes and seconds, and as a decimal hours value — handy for invoicing.
How to use the duration calculator
- Pick a mode. Add durations is for free-form sums ("how long is 1h 30m + 45m + 2h?"). Sum timecard is for adding up workdays from clock-in / clock-out / break.
- Type each row. In durations mode, accepted formats are
HH:MM:SS,HH:MM, plain minutes (a number), or compound forms like1h 30m 15s. In timecard mode, just pick start and end times and a break in minutes. - Click the
+button on a row to flip it to subtract — useful for "total minus break" or "hours worked minus hours billed". The button turns red when active. - Read the total. Beneath it, the same value is broken out into whole hours, whole minutes, whole seconds and decimal hours so you can copy whichever form your invoice or spreadsheet expects.
How the math works
Each row is parsed into seconds. In durations mode, signed rows are added together. In timecard mode, each shift is (out − in) − break; a shift that crosses midnight (out earlier than in) automatically rolls forward 24 hours. The grand total is then formatted as HH:MM:SS; a negative total displays with a leading minus sign.
Accepted duration formats
1:30 = 1h 30m. 1:30:45 = 1h 30m 45s. 90 (a plain number) = 90 minutes. 1h 30m 15s (or 1hr 30min, 1 hour 30 minutes) = the same as 1:30:15. Mix and match across rows freely.
Frequently asked questions
Can I subtract a row?
+ button at the start of a row to flip it to −. The row's value is then subtracted from the running total. Useful for things like "total session minus the time spent on breaks".What format should I type durations in?
HH:MM, HH:MM:SS, a plain number (treated as minutes), or compound forms like 1h 30m 15s. The parser is forgiving — extra spaces, mixed units (hr, hour, min, minute) and decimals (1.5h) all work.How do timecards that cross midnight work?
22:00 → 06:00 with no break gives 8 hours, exactly as you'd expect for a night shift.Can the total go negative?
What's the decimal hours figure for?
3.75 for 3h 45m). The breakdown shows that conversion next to the HH:MM:SS form so you can copy whichever your destination needs without doing the conversion manually.