 If it did half of that, if it only grew at 7% a year, the rule of 72 allows us to do some easy math here. At 7.2% interest compounded over time, your money's going to double every 10 years. They have their $700,000 secured and guaranteed, providing all the income that they need at 50 grand a year. That other $300,000 gives them a 20-year lifespan to leave those dollars alone. And the rule of 72 says that $300,000 is going to be worth $600,000 in 10 years, $1.2 million in 20 years.