How to add and subtract time
Time doesn't work in tens like normal numbers. There are 60 seconds in a minute and 60 minutes in an hour, so you can't just add times on a normal calculator: 1.45 + 1.30 gives 2.75, but 1 h 45 min + 1 h 30 min is really 3 h 15 min.
The easy way is to work in one unit. Turn everything into seconds (or minutes), add or subtract, then turn the answer back into hours, minutes and seconds. That's exactly what this calculator does.
total seconds = hours × 3,600 + minutes × 60 + seconds
hours = total ÷ 3,600 (whole number), minutes = what's left ÷ 60, seconds = remainder
Worked examples
2 hours 45 minutes plus 1 hour 30 minutes
Hours: 2 + 1 = 3. Minutes: 45 + 30 = 75. 75 minutes is 1 hour 15 minutes, so the answer is 4 hours 15 minutes (4.25 hours).
8 hours minus 2 hours 35 minutes 40 seconds
8 hours is 28,800 seconds. 2 h 35 min 40 sec is 9,340 seconds. 28,800 − 9,340 = 19,460 seconds, which is 5 hours 24 minutes 20 seconds.
What time will it be 7 hours 45 minutes after 9:30?
9:30 plus 7 hours is 16:30. Add 45 minutes to get 17:15, or 5:15 pm. If the total goes past midnight, the calculator tells you it's the next day.
Minutes to decimal hours
Payroll, invoices and timesheets often need time as a decimal. Divide the minutes by 60.
| Minutes | Decimal hours | Minutes | Decimal hours |
|---|---|---|---|
| 5 min | 0.08 | 35 min | 0.58 |
| 10 min | 0.17 | 40 min | 0.67 |
| 15 min | 0.25 | 45 min | 0.75 |
| 20 min | 0.33 | 50 min | 0.83 |
| 25 min | 0.42 | 55 min | 0.92 |
| 30 min | 0.5 | 60 min | 1.0 |
So 7 hours 20 minutes is 7.33 hours, not 7.2. Mixing these up is one of the most common mistakes on timesheets.
Tips
- Working out hours worked? The hours calculator takes start and finish times with breaks and adds up a weekly timesheet and pay.
- Counting days rather than hours? Use the date calculator for days between dates, or the days until calculator for countdowns.
- Running or cycling splits? The running pace calculator turns a finish time into pace per km or mile.
- Calling abroad? The time zone calculator converts UK time to other countries.
Frequently asked questions
How do I add hours and minutes together?
Add the hours and minutes separately, then turn every 60 minutes into an hour. 2 h 45 min + 1 h 30 min = 3 h 75 min = 4 h 15 min.
How do I convert minutes into decimal hours?
Divide the minutes by 60. For example, 45 minutes is 0.75 hours and 20 minutes is 0.33 hours, so 7 h 20 min is 7.33 hours.
How many minutes are in 2.5 hours?
2.5 hours is 150 minutes, because 2.5 × 60 = 150. That's 2 hours 30 minutes.
What time will it be in 8 hours?
Enter the current time as the starting time and 8 in the 'Plus hours' box. The calculator shows the finishing time and tells you if it's the next day.
Can I subtract a bigger time from a smaller one?
Yes. The answer is shown with a minus sign, which tells you how far short the first time is.
Last reviewed October 2026. This tool is for guidance only.