I have a single-pay loan for $2312.72. Loan Date 1/10/2012 with a single payment due 3/10/2012. Disclosed APR was 21.715% with the amount financed of $2300. It's disclosed as an "Actual / 360" loan.

When I use APRWIN, I get a violation if I enter the "Payment Frequency" as "Equal Months", but not if I enter it as "Actual Days".

I have read through the Help files and can understand that it has to do with the whole 360 / 365 day thing. So my question is: On a loan that is disclosed as "Actual / 360", should I be using a payment frequency of "Equal Months" or "Actual Days" when I use APRWIN to verify the APR? (And why?)

Your interest accrual basis does not enter into the APR calculation. When (and only when) the maturity date is an anniversary of the date of consummation, you have the choice to calculate the APR with term measured either in days or months. If you measure the time in multiples of months, you have 2/12 of a year. Because the reg permits you to count or ignore the occurrence of leap year, you would get either 60/366 or 59/365 of a year if you're measuring in days. (I don't think you can mix & match the leap year rule and get 60/365.)

That gives you 3 legally acceptable APRs:
12.72 * 100 / 2300 * 12 / 2 = 3.3183
12.72 * 100 / 2300 * 60 / 366 = 3.3736
12.72 * 100 / 2300 * 59 / 365 = 3.4214

21.715%?

Thanks for the explanation, Richard. That helps. I have been figuring out the OCC calculator as I go, and just when I think I have it figured out, something strange comes up.

Based on your comments and calculated APR's, methinks there is more going on with this loan than meets the eye. I shall have to dig deeper.

Is there some type of origination or service charge that's not reflected in the disclosed AF and FC (but is included in the APR)?