Time Calculator
Find how much time lies between two clock times, or add and subtract hours, minutes and seconds. Results are shown as a duration, in decimal days, and in total seconds.
Formula and calculation
Worked example
From 09:30 to 17:45 the difference is 8 h 15 min — that is 29,700 seconds, or 0.3438 days.
Adding time by hand
To add 1 h 45 min and 2 h 30 min: add minutes first (45 + 30 = 75), carry the extra hour (75 min = 1 h 15 min), then add hours (1 + 2 + 1 carried = 4). The answer is 4 h 15 min. Subtracting works the same way in reverse — if the minutes go negative, borrow 60 from the hours. The calculator does this carry arithmetic for you, including seconds.
What the results mean
- Result
- The time difference (or sum) as days, hours and minutes. Negative results mean the second time is earlier than the first, or the subtraction goes below zero.
- Total seconds
- The same amount in total seconds — handy for converting into software time formats.
- In days
- The amount expressed in decimal days (24 h = 1.0 day).
Frequently asked questions
How do I find the time difference between two times?
Convert both times to minutes from midnight and subtract. 09:30 to 17:45 is 17:45 − 09:30 = 8 h 15 min. If the second time is earlier, the calculator shows a negative result instead of silently adding a day.
How do I add two time durations together?
Add seconds, then minutes, then hours, carrying anything over 60 to the next unit — 45 min + 45 min = 90 min = 1 h 30 min. Switch this calculator to “Add or subtract times” and enter each duration in its own hours/minutes/seconds boxes.
Why do times like 90 minutes need converting?
Because minutes only go up to 59 in a normal time notation. 90 minutes is 1 hour 30 minutes, and 2.5 hours is 2 h 30 min. This calculator normalises the result, and also gives the raw total in seconds and decimal days for use in other tools.