Add Time Calculator: Add or Subtract Hours, Minutes and Seconds
Add or subtract durations in hours, minutes and seconds (HH:MM:SS, 1h 30m or days), as many as you need, and get the total as h m s, HH:MM:SS, minutes, seconds and decimal hours, plus the end time on the clock.
How it works
total seconds = Σ ± (days × 86,400 + hours × 3,600 + minutes × 60 + seconds) for each entry; hours = ⌊total ÷ 3,600⌋, minutes = ⌊remainder ÷ 60⌋, seconds = what is left
Each entry is converted to seconds, added or subtracted, and the total is split back into hours, minutes and seconds. Working in seconds is what makes the carry exact: 45 minutes 30 seconds plus 2 hours 15 minutes gives 3 hours 0 minutes 30 seconds, never an impossible "60 minutes". You can type HH:MM:SS, HH:MM (read as hours and minutes), D:HH:MM:SS for durations longer than a day, or words like "1h 30m", "2 hours 15 min" or "1d 4h". A plain number is read as seconds. Use the + / − buttons to subtract durations 2 and 3, and paste longer lists (one per line, a leading minus subtracts) under More options. Empty fields count as zero, and anything the calculator cannot read is listed in a note rather than silently dropped. Hours are not wrapped at 24, so 30:00:00 stays 30 hours; the "in days and hours" line and the optional start time show the day rollover.
Worked example
Adding 01:30:00, 00:45:30 and 02:15:00: 5,400 + 2,730 + 8,100 = 16,230 seconds. 16,230 ÷ 3,600 = 4 hours with 1,830 seconds left; 1,830 ÷ 60 = 30 minutes with 30 seconds left. The total is 4h 30m 30s (4:30:30), which is 270.5 minutes or 4.508 decimal hours. Starting at 9:00, the clock would read 1:30:30 PM.
Sources: Calculator.net: time calculator (add/subtract days, hours, minutes, seconds) · CalculatorSoup: add/subtract time calculator (carrying at 60 s, 60 min, 24 h) · Omni Calculator: add time calculator
Frequently asked questions
How do I add hours and minutes?
Add the minutes, and for every 60 minutes carry 1 hour; then add the hours. For example 3 h 37 min + 2 h 44 min: 37 + 44 = 81 minutes = 1 h 21 min, so the total is 6 h 21 min. The calculator does this exactly by converting to seconds first.
Can I add only two durations, or more than three?
Leave a field blank and it counts as zero. For more than three, paste one duration per line into "More durations" under More options; there is no practical limit.
What formats does it accept?
HH:MM:SS (01:30:00), HH:MM read as hours and minutes (01:30 is an hour and a half), D:HH:MM:SS for days, unit text such as 1h 30m, 90 min or 2 hours 15 minutes, and a plain number, which is read as seconds.
How do I subtract time?
Switch duration 2 or 3 to "Subtract", or start a line in the list with a minus sign. If the subtractions are larger, the result is shown as a negative duration.
How do I convert the total to decimal hours?
Divide the total seconds by 3,600, or the total minutes by 60. 4 h 30 min 30 s is 16,230 ÷ 3,600 = 4.508 hours, the figure you multiply by an hourly rate on a timesheet.
What time will it be after adding the durations?
Enter a start time of day under More options (for example 9:00 or 8:30 pm). The calculator adds the total and shows the end time in 12-hour and 24-hour form, and whether it lands on the next day.
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This calculator is for educational purposes. Double-check important results before acting on them.