Calculate the total of multiple time durations, or find a new date and time by adding or subtracting days, hours, minutes, and seconds.
Add Time Formula
This calculator works in two modes. The first adds and subtracts time durations and reports the total. The second adds a duration to or subtracts it from a starting date and time and reports the resulting date and time.
To total several durations, each duration is first converted to seconds and then summed:
T = Sum of [ s * ( (D * 86400) + (H * 3600) + (M * 60) + S ) ]
The absolute value of total seconds T is broken down into days, hours, minutes, and seconds. If T is negative, a minus sign applies to the entire normalized duration:
A = abs(T) ; Days = floor(A / 86400) ; Hours = floor((A mod 86400) / 3600) ; Minutes = floor((A mod 3600) / 60) ; Seconds = A mod 60
To find a new calendar clock time, the duration is added to or subtracted from the starting date and time, with normal day, month and year rollover. Each day is 24 hours. This calculation does not adjust for time zones or daylight saving and does not measure elapsed time between zoned timestamps:
New = Start +/- ( (D * 86400) + (H * 3600) + (M * 60) + S )
- T = total time, measured in seconds before it is normalized
- s = sign of each duration line, +1 when the duration is added and -1 when it is subtracted
- D = days entered
- H = hours entered
- M = minutes entered
- S = seconds entered
- Start = starting date and time, in seconds
- New = resulting date and time after the duration is applied
The 86400, 3600, and 60 constants are the number of seconds in a day, an hour, and a minute. Converting every value to seconds first means days, hours, minutes, and seconds can be mixed on the same line without manual carrying. Enter one duration per line, using d, h, m and s; prefix a line with minus to subtract it. Up to twenty nonempty lines are supported. In date and time mode the calendar rollover is handled for you, so crossing midnight or month boundaries moves the date forward or back automatically.
Time Unit Conversions
Every input is reduced to seconds before any math happens. These are the conversion factors the calculator uses.
| Unit | Seconds | Minutes | Hours |
|---|---|---|---|
| 1 minute | 60 | 1 | 0.0167 |
| 1 hour | 3,600 | 60 | 1 |
| 1 day | 86,400 | 1,440 | 24 |
| 1 week | 604,800 | 10,080 | 168 |
Decimal entries are allowed. The table below shows how common decimal hours convert to minutes, which is useful when a duration is recorded as a decimal instead of hours and minutes.
| Decimal hours | Hours and minutes |
|---|---|
| 0.25 h | 0 h 15 min |
| 0.50 h | 0 h 30 min |
| 1.75 h | 1 h 45 min |
| 2.10 h | 2 h 6 min |
Example Problems
Example 1: Totaling durations. You work three shifts and want the combined time. The shifts are 3 hours 45 minutes, 5 hours 30 minutes, and 2 hours 50 minutes. Convert each to seconds and add them: 13,500 + 19,800 + 10,200 = 43,500 seconds. Normalizing 43,500 seconds gives 12 hours, 5 minutes, and 0 seconds. So the three shifts total 12 hours 5 minutes.
Example 2: New time after adding a duration. A process starts at 9:30:00 on a given day and runs for 1 day, 18 hours, and 45 minutes. The duration is 1 x 86,400 + 18 x 3,600 + 45 x 60 = 154,500 seconds. Adding that to the start moves the clock to 4:15:00 and advances the date by two days, because the 18 hours 45 minutes pushes past midnight on the day after the start.
Frequently Asked Questions
Can I subtract time instead of only adding it? Yes. In total mode, prefix any duration line with minus, for example -1h 30m, and the entire duration is taken away from the running total. In date and time mode, choose subtract to move the clock and calendar backward. A total can come out negative if you subtract more than you add, and the result keeps the sign.
What happens if I leave a field blank? In date and time mode, blank numeric duration components mean zero. In total mode, omitted units on a duration line mean zero, but an empty list needs at least one duration, such as 0s. Values may contain up to six decimal places; the final result rounds to the nearest millisecond.
Does adding time roll the date over correctly? Yes. When you use date and time mode, crossing midnight moves the date forward by a day, and the same logic applies across month and year boundaries. Subtracting past midnight moves the date backward in the same way.
