>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.

Would a daily interest rate/amount do it. There may be some fine print 30/360. ACT/360/ACT/365 or ACT/ACT (leap year the daily amount is less).

If the annual dollar amount is $17, then $17/days-in-year would return the daily amount.

"B" loans are a scam:) - the lenders will sometimes include an insurance "premium" in the principal. In texas - counter loan shops do this a lot - raising the effective return from 21% to over a 100% on a one year note!:-)

Are the car loans (as suggested by Lucy) being sold at a premium or discount - sometimes insurance add ons are a premium IOW if a 100$ loan for a 100 car included a 12$ insurance premium that was amortized (not front loaded) at 1$/month - the cost per dollar loaned would be 1.08 (premium). For early pays, if the premium is to be returned to the borrower, that would decrease the total return to the lender.

Do you have a sample scenario and the expected results? If we could look at that, we might be more helpful!