Doubling Your Money This calculator demonstrates the power of compound interest. You are viewing this website at a small screen resolution which doesn't support calculators. Click here to view this calculator. Share | Related Content What Our Kids Can Teach us About Saving Money Would you guess that Millennials are effectively saving for retirement? Well, they are. Life and Death of a Twenty Dollar Bill How long does a $20 bill last? Paying Off a Credit Card Enter various payment options and determine how long it may take to pay off a credit card.