Unless you're planning to use that system for loans with a term of less than 10 yrs, Section 1026.17(c)(4)(iii) allows you to ignore any number of "short odd days" and up to 32 "long odd days." That should cover most mortgage loans for most lenders. If you think there's any possibility this system will need to calculate shorter terms, read the remaining subsections of paragraph (c)(4) and deal with your vendor accordingly. To me, software developer shortcuts like this are a big red warning sign...where else will you find design "surprises" like this?
APRWIN will verify your APRs, but you will have to:
1. manually confirm that the term of each loan and number of odd days conform with Section 1026.17(c)(4),
2. key in "1" as the number of whole unit periods and "0" odd days for the first payment stream, and
3. accept the default values APRWIN supplies for the whole and fractional unit periods for the remaining streams.
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...gone fishing.