The formula
How it works
Add or subtract two lengths of time in hours, minutes and seconds. Enter each duration, choose add or subtract, and the calculator returns the total in h:m:s along with the decimal hours and total seconds.
FAQ
Can the result be negative?
Yes. If you subtract a larger duration from a smaller one, the result is shown with a minus sign — for example, 1:00:00 minus 1:30:00 is −0:30:00. This is handy for working out how far short of a target time you are.
What are decimal hours for?
Payroll, billing and spreadsheets usually work in decimal hours rather than minutes. The calculator gives both, so 2 hours 30 minutes shows as 2.5 decimal hours — the form you would enter on a timesheet or invoice.
Can I leave minutes or seconds blank?
Yes — any field you leave empty is treated as zero, so you can enter just hours, or hours and minutes, without filling in seconds.
Can I use this to add more than two durations?
Not directly — it only combines two at a time. To total three or more, add the first pair, then use that result as one of the inputs in a second calculation.
How is this different from the Time Duration Calculator?
This tool adds or subtracts two durations you already know in hours, minutes and seconds. The Time Duration Calculator instead works out a duration from two calendar dates and clock times, such as the gap between a start and end timestamp.
What happens with values over 60 minutes or 60 seconds?
You can enter them — 90 minutes, for instance — and the calculator still adds correctly, carrying the extra time into the next unit as it converts everything to seconds internally.
Can I enter a negative number in one of the fields?
It is best to keep the individual hour, minute and second fields at zero or above and use the Subtract option to find a difference — entering a negative field directly can give confusing intermediate results.
About the time calculator
This calculator adds or subtracts two spans of time given in hours, minutes and seconds. Because time is not decimal — sixty seconds to a minute, sixty minutes to an hour — adding durations by hand means carrying across those boundaries, which is fiddly and easy to get wrong. The calculator handles the carrying for you and shows the answer several ways at once.
How to use it
Enter the first duration in hours, minutes and seconds, then the second, and choose whether to add or subtract. The result appears as h:m:s, as decimal hours and as a total number of seconds. For example, 2:30:00 plus 1:45:30 is 4:15:30, or 4.26 decimal hours. Subtracting instead gives the gap between the two durations, which may be negative.
The formula
Each duration is first converted entirely into seconds, . The two totals are then added or subtracted, , and the result is converted back into hours, minutes and seconds. Working in seconds throughout avoids the carrying errors that come from adding the columns separately, and makes the decimal-hour figure a simple division by 3,600.
Where it is used
People use it to total up task times, add legs of a journey, or work out how much time is left against a deadline. It suits anyone logging durations — from athletes adding split times to editors summing video clips and workers filling in timesheets. Any time you need to combine or compare stretches of time without slipping on the 60-minute boundary, it does the arithmetic cleanly.