About the Time Calculator
This time calculator adds and subtracts time the way a clock does, carrying 60 seconds into a minute and 60 minutes into an hour so you never have to do base-60 arithmetic by hand. Use it in duration mode to combine two lengths of time (2 h 45 min + 1 h 30 min), or in clock mode to find what time it will be after a duration (9:15 AM + 3 h 20 min) or what time it was before.
It is useful for totalling time sheets and billable hours, adding up video or podcast segments, lap and race splits, cooking and baking schedules, flight and travel legs, and working out when a shift, exam or parking session ends. Results are shown as h:mm:ss, in words, and as decimal hours, minutes and seconds for payroll and spreadsheets.
Values can exceed their normal range — 90 minutes or 200 seconds are fine — and are normalised automatically. In clock mode the result wraps around midnight and tells you if it falls on the next or previous day.
How to use the time calculator
- 1Choose Duration ± duration or Clock time ± duration.
- 2Enter the first duration, or the start time for clock mode.
- 3Pick Add or Subtract.
- 4Enter the hours, minutes and seconds to add or subtract.
- 5Read the result in h:mm:ss, words and decimal hours.
Formula and method
Each time is converted to seconds, the seconds are added or subtracted, and the total is converted back to hours, minutes and seconds. Working in seconds handles all the carrying and borrowing automatically: 45 min + 30 min is 4,500 seconds, which is 1 hour 15 minutes.
In clock mode the start time is the number of seconds after midnight. After adding or subtracting the duration, the result is wrapped into a single 24-hour day (mod 86,400 seconds) and the number of whole days crossed is reported. Decimal hours equal total seconds ÷ 3,600.
- h, m, s
- Hours, minutes and seconds
- T
- Result in seconds
- 86,400
- Seconds in one day
Worked examples
2:45:30 + 1:30:45
Seconds: 30 + 45 = 75 = 1 min 15 s. Minutes: 45 + 30 + 1 = 76 = 1 h 16 min. Hours: 2 + 1 + 1 = 4. The total is 4:16:15, or 4.2708 decimal hours.
8 h 15 min − 9 h 40 min
8 h 15 min is 495 minutes and 9 h 40 min is 580 minutes; 495 − 580 = −85 minutes, which is −1 hour 25 minutes.
10:30 PM + 3 h 45 min
10:30 PM plus 1 h 30 min reaches midnight, and the remaining 2 h 15 min takes the clock to 2:15 AM the next day.
9:15 AM − 45 minutes
Going back 45 minutes from 9:15 AM gives 8:30 AM, which is 510 minutes after midnight.
Frequently asked questions
How do I add hours and minutes together?+
Add the minutes first; if the total is 60 or more, subtract 60 and carry 1 hour. Then add the hours. For example 1 h 50 min + 2 h 25 min = 3 h 75 min = 4 h 15 min. The calculator does this carrying for you.
How do I convert hours and minutes to decimal hours?+
Divide the minutes by 60 and add them to the hours: 4 h 15 min = 4 + 15 ÷ 60 = 4.25 hours. Payroll and invoicing systems usually need decimal hours rather than h:mm.
How do I subtract time that crosses zero?+
Borrow 60 minutes from the hours column, just as you borrow 10 in normal subtraction. If the second duration is larger than the first, the result is negative, shown with a minus sign.
What time will it be in 8 hours?+
Switch to clock mode, enter the current time as the start time and 8 hours as the duration. The calculator shows the time and whether it falls on the next day.
Can I enter more than 59 minutes or seconds?+
Yes. Enter 90 minutes or 150 seconds directly and they are converted, so 90 minutes becomes 1 hour 30 minutes in the result.