Home / Everyday / Time Calculator
Time Calculator: Add or Subtract Durations
Enter two durations in days, hours, minutes and seconds, then add or subtract them. The answer is normalised, so 90 minutes becomes 1 hour 30 minutes, and totals are shown in every unit.
How time arithmetic works
Time uses mixed units: 60 seconds make a minute, 60 minutes make an hour and 24 hours make a day. Adding by hand means carrying at 60 instead of 10. The calculator avoids carrying errors by converting each duration into total seconds, adding or subtracting those, and converting back.
total seconds = days × 86,400 + hours × 3,600 + minutes × 60 + seconds
For the example above, 1:45:30 is 6,330 seconds and 2:30:45 is 9,045 seconds. Their sum is 15,375 seconds, which is 4 hours 16 minutes 15 seconds.
Decimal hours versus hours and minutes
Payroll, billing and spreadsheets often need decimal hours. To convert, divide the minutes by 60: 4 hours 15 minutes is 4.25 hours, and 4 hours 20 minutes is 4.3333 hours, not 4.20. A common mistake is reading 4.20 hours as 4 hours 20 minutes. The result table shows the decimal figure to four places so that you can round it to the precision your system expects.
Subtracting and negative results
In subtract mode the calculator computes the first duration minus the second. If the second is larger, the result is shown with a minus sign. That is useful for finding how far over or under a time budget you are. To find the length between two clock times on the same or different days, such as a shift from 22:00 to 06:00, use the hours calculator, which handles overnight spans.
Assumptions
A day here always means 24 hours. Calendar days can be 23 or 25 hours long on the days clocks change, and calendar months vary in length, so this tool does not convert to months. For gaps between calendar dates, use the days between dates calculator. Fractional entries are rounded to the nearest whole unit before the sum is taken.
Typical uses include adding up the lengths of several recordings, working out when a timer started if you know how long it has run, and checking whether a list of tasks fits inside a fixed block of time. For rota and timesheet work, convert the result to decimal hours first, then multiply by the hourly rate. Keep the sign in mind in subtract mode, because a negative total means you are over budget rather than that the calculation failed.
Worked example
A video edit takes 1 hour 45 minutes 30 seconds and the export takes 2 hours 30 minutes 45 seconds. What is the total time?
Inputs
| Operation | Add (A + B) |
|---|---|
| First duration: days | 0 |
| Hours | 1 |
| Minutes | 45 |
| Seconds | 30 |
| Second duration: days | 0 |
| Hours | 2 |
| Minutes | 30 |
| Seconds | 45 |
Result
Normalised so that minutes and seconds stay below 60.
| Clock style | 4:16:15 |
|---|---|
| Total hours (decimal) | 4.2708 |
| Total minutes | 256.25 |
| Total seconds | 15,375 |
| Total days (decimal) | 0.1780 |
Accuracy note: Results are calculated in your browser from the values you enter. Check anything that matters for legal, academic or financial purposes against the official source.
Frequently asked questions
How do I add hours and minutes together?
Add the hours, add the minutes, then carry any group of 60 minutes into an extra hour. This calculator does that automatically, including for seconds and days.
How do I subtract time?
Choose subtract and enter the larger duration first. The tool converts both to seconds, subtracts and shows the result in days, hours, minutes and seconds.
How do I convert hours and minutes to decimal hours?
Divide the minutes by 60 and add them to the hours. For example, 2 hours 45 minutes is 2.75 hours.
What does a negative result mean?
It means the second duration was longer than the first. The size of the result is the difference between them.
Can I add more than two durations?
Add the first two, then enter that result as the first duration and add the next one. Repeat until all durations are included.