Adding or Summing Time in Microsoft Excel
The biggest problem people encounter when they try to add time values is incorrect formatting of the results cell.
In our demonstration, both A1 and B1 are automatically formatted as time. A simple sum formula works fine at this point to provide a total of 4 hours.
Things change drastically when we try to add 12.5 hours to 12.5 hours, we only get a result of 1 hour.
That's because it's adding the time of day, and not hours. So if you add 12.5 hours to 12:30 on the clock, it's now 1:00 am. You wanted a result of 25 hours.
In the following demonstration, the resulting cell is formatted to properly add the hours. Note the square brackets around the hour format. If desired, just delete the last 3 characters in the Type box so you don't see the seconds values.
The only thing I've changed is the format of the resulting cell: