f = p * (1 + r) ^ n f is the future value p is the present value r is the interest rate per time period n is the number of time periods. in your problem: p = 80000 f = what you want to find r = 6.15% interest per year compounded quarterly = 0.0615/4 per quarter n = 4*18 = 72 compounding periods formula becomes f = 80000 * (1 + 0.0615/4)^72 Calculate to get f = 239991.33.