How to use the time calculator
Enter the first duration in A and the second in B, then choose Add or Subtract. Leave any unused unit blank. The result updates automatically, including totals expressed in hours, minutes, and seconds.
How adding time works
To add hours and minutes, convert both durations to seconds, add them, then convert the total back. Every 60 seconds becomes a minute, and every 60 minutes becomes an hour.
For example, 45 minutes plus 35 minutes is 80 minutes, or 1h 20m.
How subtracting time works
Subtract removes B from A. If B is larger, the difference is negative: 1h 15m minus 2h is -0h 45m, meaning negative 45 minutes.
The minus sign applies to the entire duration, not just the hours.
Converting minutes and seconds
Total seconds = hours x 3,600 + minutes x 60 + seconds
Minutes and seconds can exceed 59. Entering 90 minutes gives 1h 30m; entering 75 seconds gives 0h 1m 15s. Hours do not wrap at 24.
Total hours divide the seconds by 3,600; total minutes divide them by 60. These decimal displays use two to four places. Total seconds and the normalized duration remain exact.
Worked examples
2h 45m + 1h 30m = 4h 15m. The extra 15 minutes is 0.25 hours, so the total is 4.25 hours or 15,300 seconds.
5h 20m - 2h 45m = 2h 35m. This difference is 155 minutes, or 9,300 seconds.
1h 0m 30s + 0h 0m 45s = 1h 1m 15s. The 75 seconds carry into one minute and 15 seconds.
Frequently asked questions
Can I enter decimal or negative values?
Use whole numbers of zero or more in each field. For half a minute, enter 30 seconds. Choose Subtract to get a negative difference when B exceeds A.
Can the total exceed one day?
Yes. These are durations, not clock times. A total of 25 hours stays 25 hours instead of becoming 1:00.
What if I leave a duration empty?
All blank fields count as zero. Adding an empty duration leaves A unchanged; subtracting A from an empty duration produces negative A.
Does this calculator use dates or time zones?
No. It performs duration arithmetic only. Calendar dates, daylight saving changes, and AM/PM clock times are not involved.