Google searches are producing complex formulas that I don't understand.

It seems simple enough what I want to accomplish.

I have a calendar date selector that I wish to restrict the selection to within 7 days. I don't want the user to be able to select a date in the past or past 7 days.

My syntax started off as `=[Checkin Date]>=TODAY()` 

This works well to restrict a selection in the past. How do I add to this formula so that the user cannot select a date 7 days past the current date?

Can't seem to wrap my head around it need assistance, thanks.