Add & subtract times · HH:MM:SS · Decimal hours

Time Calculator Online

Add or subtract multiple time values. Enter each time in HH:MM:SS format and choose + or − between them. Get total in hours, minutes, and seconds.

Total Time
0:00:00
—
Decimal Hours
0
Total Minutes
0
Total Seconds
0

Tracking hours worked?

Our hours calculator works with clock-in/clock-out times and computes weekly pay.

Open Hours Calculator

Time Arithmetic: Adding and Subtracting Hours, Minutes, and Seconds

Time arithmetic is different from regular arithmetic because time uses a base-60 system for minutes and seconds, and a base-24 system for hours, rather than the base-10 decimal system we use for ordinary numbers. This means you cannot simply add time values like regular numbers: 1:45 + 1:30 is not 2:75, it is 3:15. This non-decimal nature makes time calculations error-prone when done by hand, especially when adding many time values for tasks like timesheet tracking, video editing, race planning, or project management.

The Mechanics of Time Addition

To add two time values: add the seconds; if the total exceeds 59, carry 1 into minutes and keep the remainder. Then add the minutes (including any carried value); if the total exceeds 59, carry 1 into hours. Finally, add the hours. This cascading carry logic is what makes time addition require careful attention. Subtraction works similarly but in reverse, borrowing from the next unit when necessary.

1:45:30 + 0:30:45→2:16:1530+45=75s → 1:15 carried; 45+30+1=76m → 1:16 carried; 1+1=2h.
3:00:00 − 0:45:30→2:14:30Subtract 45 minutes and 30 seconds from 3 hours.

Converting to Decimal Hours

Decimal hours (sometimes called fractional hours) express time as a decimal number of hours. This format is required for payroll calculations, billing, and many spreadsheet formulas. To convert: decimal hours = hours + minutes/60 + seconds/3600. So 2 hours, 30 minutes, and 0 seconds = 2 + 30/60 = 2.5 hours. If you bill at $80/hour and worked 2:30, your fee is 2.5 × $80 = $200.

Practical Uses for Time Addition

  • Timesheet totals — adding up daily work hours across multiple sessions to get a weekly total.
  • Video and audio production — calculating total runtime from individual clip durations.
  • Race planning — estimating total race time from expected per-segment times.
  • Cooking — calculating when to start dishes with different preparation and cooking times.
  • Sports statistics — total playing time, time on ice, minutes played in a tournament.
  • Travel — estimating total journey time from legs with layovers.

When the Result Is Negative

If you subtract more time than the total of the additions, the result is negative. For example, if you have 1:00:00 and subtract 1:30:00, the result is −0:30:00 (negative thirty minutes). The calculator displays this correctly. A negative total time result usually indicates an error in the inputs — such as a clock-out time before the clock-in time — rather than a meaningful negative duration.