How this time calculator works
Adding and subtracting time is awkward because the units do not use base ten — there are 60 seconds in a minute, 60 minutes in an hour and 24 hours in a day. The reliable way to handle it is to convert every duration into a single common unit, do the arithmetic there, then convert back. This calculator turns each row into a signed number of seconds, adds them all up, and then normalizes the total.
To normalize the total, the calculator divides the total seconds into whole days, hours, minutes and seconds, carrying and borrowing so that every leftover unit is smaller than the next unit up — seconds stay under 60, minutes under 60 and hours under 24. A row set to minus simply subtracts its seconds, so you can mix added and subtracted durations freely. If the subtractions outweigh the additions, the total is negative and is shown with a leading minus sign.
Reference note: a day is treated as exactly 24 hours and blank fields count as zero. This tool adds and subtracts durations; it does not add a duration to a calendar date or account for daylight saving changes.
Common time conversions
| Duration | Seconds | Minutes | Decimal hours |
|---|---|---|---|
| 1 minute | 60 | 1 | 0.0167 |
| 15 minutes | 900 | 15 | 0.25 |
| 1 hour | 3,600 | 60 | 1 |
| 1 hour 30 minutes | 5,400 | 90 | 1.5 |
| 1 day | 86,400 | 1,440 | 24 |
Frequently asked questions
- How do I add hours and minutes?
- Enter each duration on its own row with the hours and minutes filled in and the sign set to plus, then read the running total. The calculator converts every row to seconds, sums them, and normalizes the result back into days, hours, minutes and seconds — so 2 h 45 m + 1 h 30 m gives 4 h 15 m.
- How do I subtract time?
- Set a row's sign to minus and that duration is subtracted from the total instead of added. You can mix plus and minus rows freely, so 5 h − 1 h 30 m leaves 3 h 30 m. If you subtract more than you have added, the total is shown with a leading minus sign.
- How many minutes are in a total?
- The calculator shows the total expressed purely in minutes alongside the normalized days, hours, minutes and seconds. It divides the total number of seconds by 60, so a result of 1 hour 30 minutes is also shown as 90 minutes.
- How is the result normalized?
- Every row is converted to a signed number of seconds and summed. The total is then carried back into days, hours, minutes and seconds: 60 seconds become a minute, 60 minutes become an hour and 24 hours become a day, so the leftover units are always less than their next unit up.
- Can the total be negative?
- Yes. If the durations you subtract outweigh the durations you add, the total is negative and is shown with a leading minus sign, for example −1 h 15 m. The totals in seconds, minutes and decimal hours are negative as well.
- Does this handle days?
- Yes. Each row has a days field, and the normalized result carries every 24 hours into a day. This treats a day as exactly 24 hours, which is the standard assumption for adding and subtracting durations rather than calendar dates.