i have a spreadsheet which i want to calculate the variance between planned v actual times, i have following columns
Planned start, actual start, planned finish, actual finish, total hours, total planned hours and hours variance
the problem starts when i have a finish time after midnight, keeps returning negative total hours eg

planned start 13:00
Actual start 13:00
Planned finish 00:30
Actual finish 00:30
Total planned hours is returning -12:30, same with actual hours. I have excel using the 1904 date system but cant get this to work, anyone have any ideas?

Lawry