Hi, Per,
A day is one unit in excel time, subdividing into hours & mins & seconds. But, whatever the reason, as you were saying yourself, it does not do negative time. I am on holidays now but, at work, I did something like this: say someone has a balance of 3:00, and they take a flexi-day, say 7:30, in effect, meaning they are now 4:30 down, you can have your formula say =abs(balance - hrs taken), which gives it a positive value (4:30). In another column there will be a display of "up" or "down" based on something like this: =if(hrs taken > balance,"down", "up) placed alongside the formulas with the absolute. So the 2 columns will now display "4:30 down". Can be done. THe other way would be two use ordinary numbers and be happy to display 7:30 as 7.5, or even 7 30/60... Hope these ideas might be helpful.