Subtract the average salary of a high school graduate from your salary. This is the amount you are making additionally due to education. In 2008, the average salary was $25,000 for a high school graduate. For example, assume you make $60,000 a year, so $60,000 minus $25,000 equals $35,000.
Add together your total cost to go to college. In the example, assume college cost $100,000.
Divide the cost to go to college by the amount you make above the level of a high school graduate to calculate your payback period. In the example, $100,000 divided by $35,000 equals 2.85 years.