Time Calculator - Add or Subtract Hours, Minutes & Seconds
Add or subtract hours, minutes, and seconds, or find the duration between two clock times, with decimal-hour output.
Sum any number of time durations with per-row add or subtract toggles, and the running total normalizes automatically (90 minutes carries to 1h 30m). Results show as hh:mm:ss plus total minutes, total seconds, and decimal hours. A second mode computes the gap between two clock times, including overnight shifts that cross midnight.
This time calculator handles the two arithmetic problems clocks make awkward: stacking durations and measuring the gap between two times of day. In Add / Subtract mode you build a list of duration rows, each with hours, minutes, and seconds fields and a toggle that marks the row as added or subtracted. The running total updates as you type and normalizes overflow, so 50 minutes plus 40 minutes reads as 1h 30m, not 90 minutes. If the subtractions outweigh the additions, the total shows a leading minus instead of failing.
Alongside the hh:mm:ss total you get the same value as total minutes, total seconds, and decimal hours. Decimal hours matter for anything billed or logged numerically: timesheet software, invoices, and payroll systems usually want 7.75, not 7:45. The conversion is exact division by 3600, so there is no rounding drift between the formats.
Time between mode takes a start and end clock time and returns the elapsed duration in hh:mm and decimal hours. A crosses-midnight checkbox handles overnight spans: a shift from 22:00 to 06:00 resolves to 8 hours instead of a negative number. If the end time lands before the start time and the checkbox is off, the calculator shows the signed negative result and suggests the overnight option, so a typo never produces a silently wrong answer.
- 1
Pick a mode
Choose Add / Subtract to total a list of durations, or Time between to measure the gap separating two clock times.
- 2
Enter your times
Fill in hours, minutes, and seconds per row (toggling rows to subtract as needed), or set a start and end time and mark overnight spans.
- 3
Read and copy the result
The normalized total updates live in hh:mm:ss, total minutes, total seconds, and decimal hours. A copy button puts the result on your clipboard.
Timesheet totals
Add up a week of shift durations like 7h 45m and 8h 20m and read the payroll-ready decimal-hour figure.
Overnight shift length
Find how long a 22:30 to 06:15 night shift runs by checking the crosses-midnight option.
Editing media timecodes
Sum clip lengths in minutes and seconds to confirm a podcast episode or video cut hits its target runtime.
Race and workout splits
Subtract a split time from a finish time to see how much a pacing change cost or saved.
How does the calculator normalize overflow like 90 minutes?
All rows are converted to seconds, summed, and converted back, so 90 minutes carries to 1h 30m and 75 seconds carries to 1m 15s automatically.
Can the result be negative?
Yes. If subtracted rows exceed added ones, the total displays with a leading minus, for example -01:15:00, and the minutes, seconds, and decimal-hour figures are signed the same way.
How are decimal hours calculated?
Total seconds divided by 3600. So 7h 45m becomes 7.75 hours, the format most timesheet and billing systems expect.
What does the crosses-midnight checkbox do?
It treats the end time as falling on the next day, adding 24 hours to the span. That turns 22:00 to 06:00 into 8 hours instead of a negative result.
Is anything I enter sent to a server?
No. All arithmetic runs in your browser with plain JavaScript. The times you enter never leave your device, and the page works offline once loaded.