I see 2 ways of doing this:
A) Before you go in preview mode, create a script to total them into a field that's on the report
B) Create a calculation field that shows the date that looks like this:
If(dateField >= Get(CurrentDate) - 7;dateField;"")
Then, you can count-summarize this calculation field to get your last 7 day's count.
The B option seems to be simplest
If you do B, you would need to check the do not store calculation results box, which will make it run slower when it gets larger.
Thank you so much. It worked. I went for option B - nice and simple!