Compute the inflation adjusted annual income you will have when you retire. To do this you are simply using a future value (F V = P V (1 + r) N ) where inflation (the growth rate, or r in this case) is 4% per year. You are 20, please use a retirement age of 70 and a take home income of $33,530.45.

Next, You just figured out based on our income at (approximately 20 years old), figure out how much that would be at age 70.