Time Calculator
Add or subtract two lengths of time in hours, minutes and seconds, or work out how long it is between two clock times, with the answer also given in decimal hours, minutes and seconds.
Result
- Decimal hours
- 4.2708
- Total minutes
- 256.25
- Total seconds
- 15,375
- Breakdown
- 4 hours, 16 minutes, 15 seconds
What the time calculator does
Time does not follow the decimal system, which makes mental arithmetic with hours, minutes and seconds error-prone. This calculator adds or subtracts two durations with the correct carrying between seconds, minutes and hours, and it measures the time elapsed between a start and an end clock time, including shifts that cross midnight. Every answer is shown as h:mm:ss, as decimal hours and as plain minutes and seconds.
Method and worked example
Internally each time is converted to seconds (hours × 3600 + minutes × 60 + seconds), the arithmetic is done on the totals, and the result is converted back.
Adding durations: 2:45:30 is 9,930 seconds and 1:30:45 is 5,445 seconds. Their sum is 15,375 seconds. Dividing by 3,600 gives 4 hours with 975 seconds left, which is 16 minutes and 15 seconds, so the total is 4:16:15, or 4.2708 decimal hours.
Time between clock times: 09:00 to 17:30 is 17.5 − 9 = 8.5 hours, written 8:30:00. If the end time is smaller than the start time, 24 hours are added first, so 22:00 to 06:00 is 8 hours.
How to use this calculator
- For adding or subtracting, enter both durations and choose the operation. Leave a part at 0 if it does not apply.
- For elapsed time, enter the clock times with your browser's time picker. Seconds are optional.
- Use the decimal-hours figure for timesheets: hours worked × hourly rate. The salary calculator converts between hourly and annual pay.
Tips and limitations
- Clock-time mode handles at most one midnight crossing (under 24 hours). For longer spans use the date calculator for the days and this tool for the remainder.
- Daylight-saving changes are ignored; a shift across a clock change may be an hour longer or shorter in real life.
- Decimal hours are rounded to four places, which is well within the precision timesheets require.
Frequently asked questions
How do I add hours and minutes by hand?
Add the seconds, minutes and hours separately, then carry over: every 60 seconds becomes 1 minute and every 60 minutes becomes 1 hour. For 2:45:30 plus 1:30:45, the seconds give 75 (1 min 15 s), the minutes give 75 + 1 = 76 (1 h 16 min) and the hours give 2 + 1 + 1 = 4, so the total is 4:16:15.
What is decimal time and why is it shown?
Decimal hours express a duration as a plain number of hours, so 4 hours 15 minutes is 4.25 hours. Payroll, invoicing and timesheets usually multiply decimal hours by an hourly rate, which is why the calculator shows the result in that form too.
What happens when the end time is earlier than the start time?
The calculator assumes the end time falls on the following day, so a shift from 22:00 to 06:00 is 8 hours. If you actually meant a negative difference on the same day, swap the two times or use the duration mode with subtraction.
Can the result be negative?
Yes, in duration mode. Subtracting 1:30:00 from 1:00:00 gives −0:30:00. This is handy for checking whether you have worked more or fewer hours than planned.