It's your annual ROI. The total investment is 4 years of tuition + 4 years of opportunity cost. The total return is your salary till age 65 - salary of someon

It's your annual ROI. The total investment is 4 years of tuition + 4 years of opportunity cost. The total return is your salary till age 65 - salary of someone without a degree. Subtract 1 from 2, annualize it.