Add and subtract hours, minutes and seconds from a list of durations, with the total as H:MM:SS, decimal hours, minutes and seconds.
The 3 entries add up to 3:35:45 (H:MM:SS), which is 3.5958 hours or 215.75 minutes.
| Line | Entry | Seconds | Running total |
|---|---|---|---|
| 1 | 1:45:30 | 6,330 | 1:45:30 |
| 2 | 2:20:15 | 8,415 | 4:05:45 |
| 3 | - 0:30:00 | −1,800 | 3:35:45 |
H:MM:SS → 3600 × H + 60 × MM + SS.
12,945 s = 3:35:45
Each line is converted to seconds (3,600 × hours + 60 × minutes + seconds), lines that start with a minus sign are subtracted, and the sum is turned back into hours, minutes and seconds. Entries can be written as H:MM:SS, H:MM, 2h 15m, 90 min or 1.5 h. The total is a duration, not a time of day, so 23:59:59 plus one second gives 24:00:00 rather than wrapping to midnight.
Typical uses are adding up timesheet entries, video clip lengths, lap splits and flight legs. The default list, 1:45:30 plus 2:20:15 minus 0:30:00, totals 3:35:45, which is 3.5958 decimal hours or 215.75 minutes.
Decimal hours are the total seconds divided by 3,600, the form payroll and invoicing systems usually ask for: 7 hours 45 minutes is 7.75 hours. To find the time between a start and an end time of day, use the hours calculator instead.
Checked against: Python fractions: (6330 + 8415 − 1800) s = 12945 s = 3 h 35 min 45 s; 12945/3600 = 3.5958333…
Checked against: 86399 + 1 = 86400 s by hand
Checked against: 3600 − 9000 = −5400 s by hand
Checked against: 5400 + 5400 + 45 = 10845 s; 10845 / 60 = 180.75 by hand
Add the hours and the minutes separately, then carry every 60 minutes into an hour. 1:45 plus 2:20 gives 3 hours and 65 minutes, and 65 minutes is 1 hour 5 minutes, so the total is 4:05. Seconds carry into minutes the same way. Typing each duration on its own line here does the carrying for you.
Divide the minutes by 60. 15 minutes is 0.25 hours, 45 minutes is 0.75 hours, so 7 hours 45 minutes is 7.75 hours, and 3:35:45 is 12,945 ÷ 3,600 = 3.5958 hours. When a timesheet rounds to two decimals, each 0.01 hour is 36 seconds, so 3.5958 is entered as 3.60.
Keep the whole hours and multiply the decimal part by 60 to get minutes. 1.5 hours is 1 hour 30 minutes, 3.6 hours is 3 hours 36 minutes and 0.1 hours is 6 minutes. Type an entry such as 3.6 h on a line here to see it shown as 3:36:00.
Start the line with a minus sign. If the minutes to take away are larger, borrow 60 minutes from the hours: 2:10 minus 0:45 becomes 1:70 minus 0:45, which is 1:25. The total can go below zero; 1:00 minus 2:30 gives −1:30:00, an hour and a half short.
Excel stores a time as a fraction of a day, so a plain h:mm format wraps after 24 hours and 25 hours shows as 1:00. Format the total cell with the custom format [h]:mm:ss and the square brackets let hours run past 24. To get decimal hours in Excel, multiply the time by 24.
Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 4 worked examples whose answers come from independent sources; for example, “Two additions and a subtraction” is checked against Python fractions: (6330 + 8415 − 1800) s = 12945 s = 3 h 35 min 45 s; 12945/3600 = 3.5958333….
ISO 8601-1:2019 — durations and the extended time format hh:mm:ss; BIPM, The International System of Units (SI), 9th ed. — minute and hour as non-SI units accepted for use with the SI.
4 worked examples with independently sourced answers ship with this calculator. They run in the test suite; you can run them here too.
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