How to Use an HP 12C Mortgage Calculator

The HP 12C is Hewlett Packard's longest-selling calculator. It is specifically designed for financial calculations, including mortgage payments, the time value of money, cash flow analysis and bond calculations. The HP 12C is probably unlike any calculator you have used before, because it uses Reverse Polish Notation, called RPN. Until you learn RPN, you won't be able to perform even the simplest of computations. Once you've mastered RPN, you'll be calculating your retirement income, mortgage payments and bond yields like a pro and you won't want to go back to the old way (called "the algebraic method").

No = (Equals) Sign

Notice there is no = (equals) sign. Let's walk through an example to see how this works. Say you want to add 3 + 5. Press "3."

Press "."

Press "5."

Press "+" and the answer 8 is displayed.

A More Complicated Example

Try another another example: 6 x 7 x 8. To clear the display press "." Press "6."

Press "."

Press "7."

Press "x" (multiplication) and the answer 42 is displayed.

Press "8."

Press "x" and the answer 336 is displayed.

Calculating a Mortgage Payment

Try calculating a mortgage payment. Let's say you are going to borrow $100,000 at an interest rate of 5 percent, paid back over 20 years, and you want to calculate the monthly payments. Enter "100000."

Press "." PV is short for Present Value; it is the amount of money you borrow.

Press "20." The mortgage amortization period is 20 years.

Press "." Press "n" (n is the number of payments) and 240 appears on the display. You tell the HP 12C how many years your mortgage is, and it figures out how many monthly payments there are.

Press "5." This is the annual interest rate in percentage form.

Press "." Press "i" and 0.42 is displayed. This is the monthly interest rate in percentage form.

Press "" and -659.96 appears on the display. This is the amount of your monthly payment.


  • The key to mastering the HP 12C is mastering RPN. It takes some practice, but once you have gotten it down pat, you will understand why this calculator is a best seller for HP. As you practice this it will become second nature.