A student who is twenty years old wants to quit working when they are 60...How much will they accumulate if they invest $1,000.00 per year for the next 40 years ? What opportunity cost or compounding rate should we use ? What will the money grow at ? Use $1,000.00 a year for your calculation.. 40 as the number of periods since we assume simple interest and one compounding period per year.n=_, interest rate = %3D Approximately 10% is the average return for the S&P 500 since its inception back in 1928. Adjusted for inflation the "real return" is more like 7%. Also worth noting that nearly half of the gains from the S&P 500 resulted from dividends. 419306.78 209,653.39 199,635.11 442,592.56