General
Time Calculator
Adds and subtracts times, where the base is sixty rather than ten.
Result
Durations are treated as elapsed time, not clock times. To work out hours between a start and finish time of day, use the hours calculator instead.
Get a Free Business AuditHow the calculation works
Durations added in hours, minutes and seconds, carrying at sixty rather than at ten. The carrying is what makes time arithmetic different from decimal arithmetic, and it is where manual calculation goes wrong when minutes exceed sixty and are not carried into hours.
What moves the number
- Whether the values are times of day or durations.
- Carrying at sixty for minutes and seconds.
- Crossing midnight for times of day.
- Whether a result can validly exceed twenty-four hours.
Where this one goes wrong
A time of day and a duration are different quantities even though they look the same, since adding two times of day is meaningless while adding two durations is not, and the calculation has to know which it is working with. Be clear about it. A duration can validly exceed twenty-four hours while a time of day cannot, which is why a total of thirty hours is correct for a sum of durations and an error for a clock time.
Before you quote
- Distinguish times of day from durations.
- Carry minutes and seconds at sixty, not ten.
- Allow durations to exceed twenty-four hours.
Questions
About this calculator
Why is time arithmetic different?
Because it carries at sixty rather than ten. Adding forty minutes to thirty minutes gives one hour ten, not seventy minutes expressed as 1.10, and that carrying is where manual time calculation most often goes wrong.
Can I add two times of day?
Not meaningfully. Adding nine in the morning to three in the afternoon produces nothing useful. Durations can be added; times of day can be subtracted to produce a duration, and the two are different quantities.
Can a time total exceed 24 hours?
A duration can and should; a time of day cannot. A total of thirty hours is correct for a sum of durations and an error for a clock time, which is why the calculation needs to know which it is producing.
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How to use this calculator
- First duration: hours. Enter your own figure; the page starts at 2.
- First duration: minutes. Enter your own figure; the page starts at 45.
- Operation. Enter your own figure; the page starts at Add (+).
- Second duration: hours. Enter your own figure; the page starts at 1.
- Second duration: minutes. Enter your own figure; the page starts at 30.
The result updates as you type, so you can try a figure, see what it does to result, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| First duration: hours | 2 |
| First duration: minutes | 45 |
| Operation | Add (+) |
| Second duration: hours | 1 |
| Second duration: minutes | 30 |
What comes out
| Result | Value |
|---|---|
| Result main result | 4h 15m |
| As decimal hours | 4.25 |
| Total minutes | 255 |
| As days | 0.177083 |
The result is 4h 15m, which is 4.25 decimal hours.
How sensitive the answer is
Holding everything else steady and changing only first duration: hours, this is what happens to result. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| First duration: hours | Result |
|---|---|
| 1 | 3h 15m |
| 2 | 4h 15m |
| 2 example above | 4h 15m |
| 3 | 5h 15m |
| 4 | 6h 15m |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- First duration: hours
- A number, between 0 and 100000, starting at 2.
- First duration: minutes
- A number, between 0 and 59, starting at 45.
- Operation
- Choose from Add (+), Subtract (−).
- Second duration: hours
- A number, between 0 and 100000, starting at 1.
- Second duration: minutes
- A number, between 0 and 59, starting at 30.
What the results tell you
| Result | What it is |
|---|---|
| Result | The headline result. A category or planning selection, rather than a measured quantity. |
| As decimal hours | A number. |
| Total minutes | A number. |
| As days | A number. |
Keep going
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