Create a rolling date period

[JPL3]

Using a pivot table in Excel 10 to look at totals by date. I want to look at sales for the last 7 days. I right click a date, select Filter, then Date Filters and the date filter window opens, that offers me options. I want to use "Is Between" then use something like =Today() and =Today()-7, but it only lets me enter hard dates. Will those Filter fields accept function (DAX?) or only hard dates, and if so, how do you establish a rolling window of time?

Thanks in advance

jpl