Calculate Due Date On Form

I have a form (frm_Active) that reads from a query (qry_Active) based on a table (tbl_Data). The form/query/table has the following fields:

EVENT DATE
START_DATE
REVIEW_DATE
APPROVED_DATE
POST-REVIEW_DATE

When I add a new record, I would like for the default dates to be populated based on the EVENT_DATE. For example, if I enter 1/1/2006 for the EVENT_DATE, I want the

START_DATE = +7 days
REVIEW_DATE = +55 days
APPROVED_DATE = +60 days
POST-REVIEW_DATE +180 days

I tried to do this in the table as the "default value" and it would not accept it. I don't think I can do this in the query because the query is basically displaying the table and I want to be able to manually enter a different date if needed so it will be stored in the table. I tried this on the form in the "Default Value" field, but it is just blank when I enter a new record and enter the EVENT_DATE. However I am not sure I am entering the formula correct. Can someone tell me what is the best way of doing this and what the correct formula is?

Thanks,
Jim