Help with "if" formula in web form.

I am trying to get a web form to add a late fee when needed and having trouble. My formula is as follows if ([Date Signed] < [Cut Offa], "100.00","0.00")

What i want is it to add $100.00 if the date the doc is signed (Date Signed) is after a pre established Cut off date(Cut Offa). It somewhat works as it adds the $100 regardless of whether the cut off is before or after the signed date. I haveto be missing somethig stupid. Thanks in advance for your help!