# Calculating how long it’ll take you to pay off a loan

The calculator below calculates the number of months it takes to pay off a loan debt (for example, a credit card balance); it is based on equation (3.14) in *The Calculus of Happiness*. The result depends on the loan amount, current monthly payment, and the interest rate on the loan (expressed as a decimal). Input those values into the **green** cells to see how long it would take to pay off the loan.

In Section 3.2.3 of *The Calculus of Happiness *I use the formula the calculator below is based on (equation (3.14) in teh book) to illustrate how increasing the monthly payment even by as little as $5 can save you *months* of payments (and all the interest associated with them). Specifically, I calculate that paying $5 more than the $20 minimum monthly payment due for a $1,000 credit card debt at a 12% annual interest rate reduces the payoff time by 18.4 months!

## Limitations

This calculator assumes that the monthly payments and interest rate are fixed for the life of the loan.