How to add and subtract time
Because time uses base 60, you cannot add 1:45 and 2:30 like ordinary decimals. The reliable method is to convert everything to the smallest unit, add or subtract, then convert back:
- Convert each value to seconds: hours × 3600 + minutes × 60 + seconds.
- Add or subtract the totals.
- Convert back: divide by 3600 for hours, take the remainder ÷ 60 for minutes, and what's left is seconds.
Example: 2 h 45 min + 1 h 30 min = 9,900 s + 5,400 s = 15,300 s = 4 h 15 min (4.25 decimal hours).
Subtracting: 5 h 10 min − 2 h 35 min. Borrow an hour: 4 h 70 min − 2 h 35 min = 2 h 35 min.
What people use the time calculator for
- Adding up hours worked across several jobs or tasks for an invoice.
- Totalling video, podcast or music track lengths.
- Adding lap, split or workout times.
- Working out how much time is left in a project budget.
Need the time between two clock times instead? Use the hours calculator. To find what time it will be after adding hours to the current time, use hours from now.
Frequently asked questions
How do you add hours and minutes together?
Add the hours and minutes separately. If the minutes total 60 or more, subtract 60 and add 1 to the hours. Example: 3:40 + 2:35 = 5 h 75 min = 6 h 15 min.
What is 1 hour 45 minutes plus 2 hours 30 minutes?
4 hours 15 minutes, or 4.25 hours in decimal.
How do I convert the result to decimal hours?
Divide total minutes by 60. The calculator shows decimal hours automatically – for example 4 h 15 min is 4.25 hours.
Can the result be negative?
Yes. If you subtract more time than you added, the result is shown with a minus sign, which tells you how much time you are short.