Since the function library in Forms doesn't contain an equivalent to MS Excel's PMT function, I'm trying to put together one long-hand. Here's the standard equation:

P = (Pv*R) / [1 - (1 + R)^(-n)]

Forms Variables are:

**Pv**= Loan_Amount**R**= Fixed_Rate/Payment_Frequence (Payment_Frequency is a drop-down field with word values that I'm assigning numeric values to)**n**= Ammortization (total number of payments over life of the loan)

Here's the formula I've come up with. I did it based on 1/(1+R)^n instead of (1+R)^(-n) just in case Forms couldn't handle the negative exponent.

DIV(MULT(Loan_Amount,DIV(Fixed_Rate,Payment_Frequency)),SUB(1,DIV(1,POWER(SUM(1,DIV(Fixed_Rate,Payment_Frequency)),(Amortization)))))

I keep getting a calculation error, though it's not telling me where the issue is. Any ideas where I'm going wrong?