Subtracting days from the current date

[cousinconley]

I am trying to create a Crystal Report that has a series of formulas that will tract amounts posted to an account in a MAS200 database. I need to have a formula that will pull the account amount 7 days ago, then one that will do it 6 days ago, etc. I need to do this based on the current date or possibly a paramenter date value if the currentdate cant be done.

This is what I have so far:
IF {GL4_DailyPosting.AccountNumber} LIKE "446**-40-40" AND {GL4_DailyPosting.TransactionDate}=CurrentDate-7 then {GL4_DailyPosting.PostingAmount}