### Title

FINANCIAL; Formula to find APR%

### Post

I am looking to find what the APR is given the fact that I know the number of MONTHS, the PRINCIPAL, the FINANCE CHARGE and the AMOUNT OF MONTHY PAYMENTS.

$9,000.00 IS THE PRINCIPAL

$3,960.00 IS THE AMOUNT OF INTEREST

$270.00 ARE THE MONTHLY PAYMENTS

48 IS THE NUMBER OF MONTHS

In this case I know the answer is 19.19%, but I need the formula that I can program in Filemaker Pro so that I can use in many different scenarios. I am not a math wiz and I am stumped. I have a link to view an online calculator that does this and gives the correct formula but I can't translate it to Filemaker format.

http://www.efunda.com/formulae/finance/loan_calculator.cfm

Also in excel the formula seem simple enough

=RATE(MONTHS,PAYMENTS,PRINCIPAL)*12 >>>RETURNS 19.19%

Someone please help me, I'll greatly appreciate it.