How time maths works
Time is counted in sixties, not tens: 60 seconds make a minute and 60 minutes make an hour. That is why you cannot add times like ordinary decimals. The calculator turns everything into seconds, does the sum, then turns the answer back into hours, minutes and seconds.
To go back, divide by 3,600 for whole hours, take the remainder and divide by 60 for minutes, and what is left is seconds.
Worked examples
Adding two durations
2 h 45 min 30 s plus 1 h 30 min 45 s:
- Seconds: 30 + 45 = 75 s, which is 1 min 15 s. Write 15 s and carry 1 minute.
- Minutes: 45 + 30 + 1 = 76 min, which is 1 h 16 min. Write 16 min and carry 1 hour.
- Hours: 2 + 1 + 1 = 4 h.
The answer is 4:16:15, or 15,375 seconds.
An overnight shift
A shift starts at 22:30 and ends at 06:15 the next morning, with a 30-minute unpaid break. The end time is earlier than the start, so the shift crosses midnight:
That is 7 hours 15 minutes, or 7.25 hours on a timesheet.
A time plus a duration
A train leaves at 21:30 and the trip takes 3 h 45 min. 21:30 + 3:45 = 25:15, which is past 24:00, so the train arrives at 01:15 the next day (1:15 AM).
Decimal hours and hours:minutes
Payroll systems and invoices often use decimal hours, where the part after the point is a fraction of an hour, not minutes.
| Minutes | Decimal hours |
|---|---|
| 6 min | 0.1 |
| 10 min | 0.167 |
| 15 min | 0.25 |
| 20 min | 0.333 |
| 30 min | 0.5 |
| 40 min | 0.667 |
| 45 min | 0.75 |
| 50 min | 0.833 |
A common mistake is reading 7.30 as seven and a half hours. In decimal hours, 7.30 is 7 hours and 18 minutes; seven and a half hours is 7.5. If a payslip and your own notes disagree, check which format each one uses.
Using the timesheet
The timesheet adds up as many entries as you like. Each row accepts:
- Clock style:
7:30(7 hours 30 minutes) or7:30:15with seconds. - Decimal hours:
7.5or7,5. - Units:
7h 30m,90 min,45sor2 days 3 hours. - Corrections: start with a minus sign, like
-0:30, to take time off.
Add an hourly rate to see the pay for the total. For example, 38.5 hours at 15.50 an hour is 38.5 × 15.50 = 596.75 before tax. To see what that leaves after tax, try the paycheck calculator.
Some employers round each shift, for example to the nearest quarter hour. If yours does, enter the rounded times so the total matches your payslip.
Tips
- Same start and end time? The calculator shows 0. If it was really a full 24-hour shift, the time worked is 24:00.
- Your device decides 12 or 24 hours. The time boxes follow your phone or computer settings, and results are shown in both formats.
- Counting days, not hours? The date calculator counts the days and business days between dates.
- Timing something live? Use the online timer for a countdown with an alarm, or its stopwatch with lap times.
- Counting days by hand? The guide on how to count days between dates explains inclusive counts and business days.
All the maths happens in your browser, and nothing you type is sent anywhere.