{delenda est}

>Can anyone provide me with a formula to determine 'same yield' APR on the same principal amount but with different payment intervals ( 1 monthly the other weekly) over the same loan period. At this point I know two things for certain. 1= Coming up with an APR that will result in the same Finance charges is incorrect. 2= Using the formula for determining effective annual return (EAR) does not work either.

From my work in the motor trade here (we don't have anything like the same rules but depreciation rules have some similarities), and some work with financials I'd build a table of factors which increase or decrease depending on whether the payment is early or late and relating to the APR that it has to meet. This undoubtedly will include some fudge factor for fortnightly figures in relation to calendar month when the month is five weeks. That fudge factor is probably calculable but whether you'd come up with the same as the official figure is doubtful.

So because of that, I'd hit them with a request under the Freedom of Information Act (I'm not american so IANAL definitely applies), my understanding is that a taxpayer has the right to see that information. Perhaps it would mean one of your clients in the state making the request on your behalf.