hi
would have been nice if you had posted your formula so someone might see
what your are doing wrong.

excel keeps time as a decimal value of a day.
12 hrs = .5 day

assuming that your date/time that you are subtracting is A....
=IF(B1A1,A1-0.5,0)

post back with more details. maybe we can refine it more.

regards
FSt1


"Cindy" wrote:

I am trying to subtract 12 hours from a date/time cell if the date in B1 is
greater than A1.

A1 3/3/2010 2030 (formatted: m/d/yyyy hh:mm)
B1 3/4/2010 1030 (formatted: m/d/yyyy hh:mm)

No matter how I format A1, B1 and C1 I still get a #Value error. I am
obviously missing something or leaving something out. Any help is greatly
appreciated.

Cindy