If a person starts investing $100 per month starting at age 21, and that money earns a 7% 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 future worth of money with the investment made every year can be calculated through the equation,
            F = A x ((1 + r)^n - 1/ (r))
Substituting the known values,
            F = ($1200) x ((1 + 0.07)^49 - 1) / (0.07))
                  F =  $454,798.8 

Hence, the future worth of the made contribution is $454,798.8.