MEMORANDUM ***

Stephen Yagman owes the United States approximately $22,500. A portion of that debt is offset against his monthly Social Security benefit pursuant to 31 U.S.C. § 3716(c)(3)(A)(i). Yagman sued in the district court, raising a variety of chai-, lenges to the offsets. He eventually pursued only a claim under the Administrative Procedure Act, which the district court dismissed pursuant to Federal Rule of Civil Procedure 12(b)(6). We review the district court’s decision de novo. See Edwards v. Marin Park, Inc., 356 F.3d 1058, 1061 (9th Cir. 2004).

1. 31 U.S.C. § 3716(c)(3)(A)(ii) makes $9,000 per year — or $750 per month — “exempt from offset.” The plain meaning of that phrase is that $750 of a debtor’s monthly benefit cannot be withheld as an offset. The statute does not refer to the 15% cap contained'in 31 C.F.R. § 285.4(e), let alone dictate the base on which the cap is to be calculated.

Thus, the statutory exemption guarantees only that a debtor will receive a monthly benefit of at least $750 notwithstanding the debt. Since Yagman has always received far in excess of that amount, the calculation of his offsets complies with the statute’s unambiguous command.

2. Yagman’s argument that § 285.4(e) is arbitrary and capricious because the agency did not articulate a rationale for the 15% cap was not raised below and may be disregarded. See Peterson v. Highland Music, Inc., 140 F.3d 1313, 1321 (9th Cir. 1998). In any event, the agency’s statement that Social Security beneficiaries “may be dependent upon their Federal benefits for a substantial part of their income,” Offset of Federal Benefit Payments To Collect Past-due, Legally Enforceable *684 Nontax Debt, 63 Fed. Reg. 44986, 44987 (Aug. 21,1998), explained the rationale for the cap.

3. Yagman’s challenge to the notiee- and-comment procedure by which § 285.4(e) was promulgated also was not raised below. Had it been, it would have been untimely. See Wind River Min. Corp. v. United States, 946 F.2d 710, 715 (9th Cir. 1991).

4. Finally, Yagman’s contention that the offsets were not authorized by an agency head also was not raised below. In any event, it is without merit. AFFIRMED.