20 C.F.R. § 418.3101
How do you become eligible for a subsidy?
Unless you are deemed eligible as explained in § 418.3105 and 42 CFR 423.773(c), you are eligible for a Medicare Part D prescription drug subsidy if you meet all of the following requirements:
(a) You are entitled to or enrolled in Medicare Part A (Hospital Insurance) or enrolled in Medicare Part B (Supplementary Medical Insurance) or both under title XVIII of the Act.
(b) You are enrolled in a Medicare prescription drug plan or Medicare Advantage plan with prescription drug coverage. We can also determine your eligibility for a subsidy before you enroll in one of the above programs. However, as explained in § 418.3225(b), if we determine that you would be eligible for a subsidy before you have enrolled in a Medicare prescription drug plan or Medicare Advantage plan with prescription drug coverage, you must enroll in one of these plans to actually receive a subsidy.
(c) You reside in the United States as defined in § 418.3010.
(d) You (and your spouse, if applicable) meet the income requirements as explained in §§ 418.3301 through 418.3350 and 42 CFR 423.773.
(e) You (and your spouse, if applicable) meet the resources requirements as explained in §§ 418.3401 through 418.3425 and 42 CFR 423.773.
(f) You or your personal representative file an application for a subsidy as explained in §§ 418.3201 through 418.3230.