How to calculate amount of day’s in form based on table

I want to calculate the amount of day’s between 2 dates in a access 2003 form which is based on a table.

In the form I have entered a date. Next session I will enter a second date. I want the form to tell me when I have entered the second date, how many days have elapsed between date 1 and date 2. I want this to be shown in a textbox,but this number doesn’t need to be saved in the table. The dates are saved in the table. Thank for helping.