How do I calculate time in Excel?

[Guest]

I am trying to show the difference between required hours and extra time
worked.
I have the first part done. End time-start time=hours worked. So
5:00pm-8:00am=9:00.

How do I subract 7.5 hours from 9:00. I've already tried 9:00-7:30 (or the
cell reference thereof) but no luck.

I'm sure this isn't hard, but I can't seem to get my head around it.

Thanks!

 

[Guest]

Hi
if both cells contain time values try:
=A2-A1+(A2<A1)