Date subtraction

I must be having a bad day, because for some reason I my brain has shut me out of all simple excel formulas...

What I want to do is figure out how many days are in between two dates. In one column I have a specific date, and I want to subtract that from another specific date, not located in any cell.

For instance, in cell N3 I have 20-Apr-11 and I want my current cell to display the difference from 21-Apr-11, which would be 1.

I have done this MANY times before, I just can't for the life of me do it now, I feel so dumb

If you are using today's date, you can use either:

=DATEDIF(N3,TODAY(),"d")

or

=TODAY()-N3

you can replace TODAY() with DATE(2011,4,21) if you are looking at a specific date.