Debt Investment Calculator Before you go throwing darts on Wall Street, check to make sure you can't earn a higher rate of return simply by investing in your own debt! For example, if you have a credit card balance that's costing you 19% per year, and you increase your payment, you will get a guaranteed 19% return on your investment. What's more, your earnings will be tax-free! So use this JavaScript Calculator to see how much you could be earning if you increased your payment on any one of your debts. Enter the principal balance owed: Enter the annual interest rate: Enter the current monthly payment amount: Enter a monthly amount to add to the current payment: Total interest savings (Return on investment): Guaranteed Annual Rate of Return: