If a person starts investing $100 per month starting at age 21, and that money earns a 5% return every year, how much will this person have when turning 70 years old? For ease of calculation, assume starting balance of $0 and annual contributions of $1,200 (12*$100).

The formula for calculating compound interest with yearly contributions is:Balance = X*(1 + Y)^n + Z((1 + Y)^(n + 1) - (1 + Y)/Y)where the balance is the money earned after n years investedY is the interest rate as a fractionZ is the yearly contributionX is the starting investmentTherefore the calculation for this example is:Balance = 1200*(1 + 0.05)^48 + 1200((1.05)^49 - (1.05)/05)
= $249,393.5