There are two ways to evaluate the number of days for such an interval. It's a matter of whether an interval such as:
Start Date = 7/1/14, End Date = 7/2/14 represents an interval of one day or two. This calc evaluates that as 1 day, not 2 so in your case you may need to add 1 to your result if the start date counts as one of the days.
To PhilModJunk- in case I forgot as I have been a little swamped, thank you for your help I did not realize that the interval did not include day 1. Again thanks