How the calculation works
The calculator turns each time into seconds, adds or subtracts them and then splits the result back into days, hours, minutes and seconds. For a time of day it adds the duration to the start time and wraps around at midnight.
Seconds = days × 86,400 + hours × 3,600 + minutes × 60 + seconds
Result = first ± second, then split into days, hours, minutes and seconds
For a time of day the result is taken modulo 24 hours. The number of whole days that wrap around is shown as days later or earlier.Worked examples
Adding times: 2 h 45 min + 1 h 30 min.
- In seconds: 9,900 + 5,400 = 15,300.
- 15,300 seconds is 4 hours (14,400) and 900 seconds, which is 15 minutes.
- Result: 4 h 15 min, or 4.25 hours.
Time of day: 22:30 plus 3 h 45 min.
- 22:30 plus 3 hours is 01:30, and 45 minutes more is 02:15.
- The clock passed midnight once, so the result is 02:15, 1 day later.
What this calculator does not include
- Calendar dates, months and years. It works with days of exactly 24 hours.
- Daylight saving time and time zones.
- Leap seconds.
Amounts are rounded for display only; the calculation itself is not rounded. Results are estimates for information, not financial advice. Last updated: 12 November 2026.
Frequently asked questions
How do I add times when the minutes go over 60?
Every 60 seconds make a minute and every 60 minutes make an hour, so the extra is carried over. 2 h 45 min plus 1 h 30 min is 3 h 75 min, which is 4 h 15 min. The calculator does the carrying for you.
Can the result be negative?
Yes. If you subtract a longer time from a shorter one, the result has a minus sign. For example, 1 h 30 min minus 2 h 45 min is −1 h 15 min.
How do I find the time after a duration?
Choose "Time of day", enter the start time on the 24-hour clock and the duration, and pick plus or minus. If the new time falls on another day, the calculator tells you how many days later or earlier it is.
How do I turn hours and minutes into decimal hours?
Divide the minutes by 60 and add them to the hours. 1 h 30 min is 1.5 hours and 2 h 45 min is 2.75 hours. The result shows the total in hours, minutes and seconds.
Does it handle daylight saving time?
No. It treats every day as exactly 24 hours. If a clock change falls inside your period, the real time can differ by an hour.