Official Staff Commentary 226.32(a)(1)(i).
4. Treasury securities. To determine the yield on comparable Treasury securities for the annual percentage rate test, creditors may use the yield on actively traded issues adjusted to constant maturities published in the Board's "Selected Interest Rates" (statistical release H-15). Creditors must use the yield corresponding to the constant maturity that is closest to the loan's maturity . If the loan's maturity is exactly halfway between security maturities, the annual percentage rate on the loan should be compared with the yield for Treasury securities having the lower yield. In determining the loan's maturity, creditors may rely on the rules in ยง226.17(c)(4) regarding irregular first payment periods. For example:
i. If the H-15 contains a yield for Treasury securities with constant maturities of 7 years and 10 years and no maturity in between, the annual percentage rate for an 8-year mortgage loan is compared with the yield of securities having a 7-year maturity, and the annual percentage rate for a 9-year mortgage loan is compared with the yield of securities having a 10-year maturity.
ii. If a mortgage loan has a term of 15 years, and the H-15 contains a yield of 5.21 percent for constant maturities of 10 years, and also contains a yield of 6.33 percent for constant maturities of 20 years, then the creditor compares the annual percentage rate for a 15-year mortgage loan with the yield for constant maturities of 10 years.
iii. If a mortgage loan has a term of 30 years, and the H-15 does not contain a yield for 30-year constant maturities, but contains a yield for 20-year constant maturities, and an average yield for securities with remaining terms to maturity of 25 years and over, then the annual percentage rate on the loan is compared with the yield for 20-year constant maturities.
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The opinions expressed are mine and they are not to be taken as legal advice.