How adding time works
To add two durations, sum the seconds, then the minutes, then the hours, carrying over whenever a column reaches 60. For example 1 h 30 m + 2 h 45 m = 4 h 15 m because 30 + 45 = 75 minutes, which is 1 h 15 m carried into the hours.
A longer example: 3 h 47 m 38 s plus 1 h 25 m 45 s. Seconds first: 38 + 45 = 83 s, which is 1 m 23 s, so write 23 s and carry 1 minute. Minutes: 47 + 25 + 1 = 73 m, which is 1 h 13 m, so write 13 m and carry 1 hour. Hours: 3 + 1 + 1 = 5. The total is 5:13:23.
For the same task from a slightly different angle, try the subtract time calculator.
How to use this calculator
Enter both durations as hours, minutes and seconds. The total appears in H:MM:SS with carry-over already applied. To convert the answer into decimal hours, use the minutes to hours calculator, or check a shift length with the work hours calculator.
Common uses include totalling billable time across several tasks, adding travel legs to find a door-to-door journey time, stacking cooking stages to work out when a dish will be ready, and summing lap or split times from a training session. Enter a duration rather than a clock time: 90 minutes of driving goes in as 1 h 30 m, not as 13:30.
Why carry-over matters
Time is base-60 for minutes and seconds, not base-100. Adding 40 minutes to 40 minutes gives 80 minutes, which is really 1 h 20 m. This calculator handles every carry automatically so you never end up with an impossible value like 1:75.
The same base-60 rule is why 0.5 hours is 30 minutes and not 50, and why a shift logged as 7.75 hours is 7 h 45 m. If you need the answer as a decimal for payroll, divide the minutes by 60 and add them to the hours: 4 h 15 m becomes 4.25 hours.
If you are checking your work, the time duration calculator gives you a second reference point.
Frequently asked questions
- What is 1:30 plus 2:45?
- 1 hour 30 minutes plus 2 hours 45 minutes equals 4 hours 15 minutes (4:15:00).
- How do I add two durations together?
- Add the seconds, minutes and hours separately, carrying over to the next unit whenever a column reaches 60.
- Does it carry over past 60 minutes?
- Yes. If minutes exceed 60 they roll into hours, and seconds over 60 roll into minutes automatically.
- Can I add seconds too?
- Yes. Each duration has hours, minutes and seconds fields, and seconds carry into minutes when they reach 60.
- Why does my spreadsheet give a different total?
- Usually because the durations were typed as decimals instead of base-60 values. 1.30 + 2.45 as plain numbers is 3.75, but 1 h 30 m + 2 h 45 m is 4 h 15 m. Convert to decimal hours first if you want to add times with ordinary arithmetic.