mysql> select abs(to_days(date_1) - to_days(date_2)) - 2 * abs(week(date_1) - week(date_2));
where date_1 and date_2 are your two date columns in MySQL. I threw in the abs() just in case you didn't know which date was sooner. You can use NOW() for one of the dates to find it relative to the current date. Hope that helps.
---John Holmes...