Calculating Rates of Return In 2018, one of the first copper pennies struck at the Philadelphia mint in 1793 was sold for $300,000. What was the rate of return on this investment? Calculating Rates of Return Assume the total cost of a college education will be $235,000 when your child enters college in 18 years. You presently have $53,000 to invest. What annual rate of interest must you earn on your investment to cover the cost of your child's college education?