An HP 12c is a financial calculator that can figure the time value of money problems and compound interest calculations. Compound interest is common in bank accounts and loans, where you earn interest on top of both the principal amount in the account and on the interest you previously earned. By using the HP 12c, you can quickly calculate compound interest without needing to use the complex compound interest formula.

Press "f," "Clear" and "Fin."

Enter the number of years you are compounding, then "g" followed by "12^x." This enters the number of periods for your loan.

Enter your annual interest rate per year, then "g" followed by "12/." The screen will display your interest rate per month.

Enter the original amount you had in the account and press "PV."

Enter any cash you pay into the account. Be sure to put a negative sign in front of cash paid in. If you paid any cash out of the account, make the number positive. Then press "Chs" and "Pmt."

Press "g" and then "End" if you make the payments at the end of the period. Press "g:" and then "Beg" if you make payments at the beginning of the period.

Press "FMV" to get the accounts value, plus compound interest, at the end of time period set.