Add the number of cars (new or used) you have purchased FOR YOURSELF to the number of PRIMARY residences you have purchased since graduation and subtract the number of years since graduation. DO NOT include cars or houses purchased for parents/spouses/children, etc.
For example, you graduated in 1995 and since that time you have bought/leased 4 cars and 2 primary residence properties.
4 + 2 - 17 = -11.
My number is -18. I've got a sister-in-law that graduated a year ahead of me that is well into positive numbers.