Time calculator
Add or subtract durations, or add time to a clock.
- Hours, minutes and seconds
- Add time to a clock reading
- Flags next-day or previous-day results
How to calculate with time
- Pick duration math or a clock time plus a duration.
- Enter the hours, minutes and seconds.
- Read the result instantly.
Carrying seconds and minutes
Time carries in base 60. Every 60 seconds roll over into a minute and every 60 minutes into an hour, the same way a spreadsheet or stopwatch counts. Subtraction borrows the other way: 1 minute becomes 60 seconds, 1 hour becomes 60 minutes.
The safest method by hand is to convert everything to seconds, do the sum, and convert back. 3:45:30 is 13,530 seconds and 2:20:45 is 8,445 seconds. Their sum, 21,975 seconds, is 6:06:15.
| Calculation | Carry or borrow | Result |
|---|---|---|
| 2:30:00 + 1:45:00 | 75 min = 1 h 15 min | 4:15:00 |
| 3:45:30 + 2:20:45 | 75 s = 1 min 15 s, then 66 min = 1 h 6 min | 6:06:15 |
| 1:50:40 + 0:25:35 | 75 s = 1 min 15 s, then 76 min = 1 h 16 min | 2:16:15 |
| 4:05:10 - 2:30:50 | Borrow 60 s from the minutes, then 60 min from the hours | 1:34:20 |
| 0:30:00 - 1:15:00 | Second duration is longer | -0:45:00 |
Duration mode vs clock mode
Duration mode treats both values as lengths of time, so there is no ceiling. 22:00:00 plus 3:30:00 is 25:30:00, which is what you want when totaling hours worked, a playlist or a long drive.
Clock mode treats the first value as a time of day and wraps at midnight. 10:00 PM plus 3 hours 30 minutes shows 1:30 AM with a note that it lands on the next day. Going the other way, 1:00 AM minus 2 hours 30 minutes shows 10:30 PM on the previous day. Results use the 12-hour AM and PM format.
Everyday uses for time math
- Adding a marinade time to a cook time to see when dinner is ready.
- Totaling the segments of an interval workout.
- Checking a layover by subtracting the landing time from the next boarding time.
- Adding a movie or podcast runtime to a start time to find when it ends.
Mistakes when adding hours and minutes
- Treating a duration as a decimal. 2.30 hours is 2 hours 18 minutes, since 0.3 of an hour is 18 minutes.
- Leaving 75 seconds or 75 minutes in a column instead of carrying 60 of them up.
- Missing that a clock result crossed midnight, which changes the date even though the time looks normal.
Time calculator FAQ
What is 2 hours 30 minutes plus 1 hour 45 minutes?
2:30:00 + 1:45:00 = 4:15:00, or 4 hours 15 minutes.
What time is 5 hours 30 minutes after 9:00 AM?
9:00 AM plus 5 hours 30 minutes is 2:30 PM.
What happens if the result crosses midnight?
The clock time wraps around and a note tells you the result lands on the next day or the previous day.
Can the duration result be negative?
Yes, when subtracting a longer duration from a shorter one. The result shows a minus sign, like -0:45:00.
What is 3 hours 45 minutes 30 seconds plus 2 hours 20 minutes 45 seconds?
6:06:15, or 6 hours, 6 minutes and 15 seconds.
What is 5 hours 15 minutes minus 1 hour 45 minutes 30 seconds?
3:29:30, or 3 hours, 29 minutes and 30 seconds.
What time is 3 hours 45 minutes after 11:30 PM?
3:15 AM, and it lands on the next day, since adding the duration crosses midnight.
Can I add more than two durations at once?
This tool combines two durations at a time. For three or more, add the first two, then add that result to the next duration, repeating until every duration is included.