I am banging my head on this one. I need a simplified way to express a Log() function and as I am getting older, my head isn't working as well as it used to (if it ever worked at all).

I'm trying to figure out the calculation for a customer who pays extra on a loan, how many month will it take to pay it off. I am using this:

(Log ( extraPayment ) - Log ( extraPayment - ((CurrentBalance * InterestRateCalc ) / 12)) ) /

Log ( 1 + (InterestRateCalc / 12))

This works great but the software using the DDR that I generate doesn't like LOG() or any other financial functions. I also know of the function NPER() that works with excel but that won't work with filemaker. Any help would be awsome.

the software using the DDR that I generate doesn't like LOG() or any other financial functions

Log() is not a financial function - it is a math operation (and a rather basic one in a computing environment that cannot lookup a logarithmic table). It is also not clear why another application must use the same formula you are using in Filemaker.

Anyway, to calculate - or rather approximate - the logarithm, see:

http://en.wikipedia.org/wiki/Logarithm#Calculation