42 CFR §409.64

1. (a)Except as provided in paragraph (b) of this section for lifetime reserve days, all covered inpatient days and home health visits are counted toward the allowable amounts specified in §§ 409.61 through 409.63 if—
   1. (1)They are paid for by Medicare; or
   2. (2)They would be paid for by Medicare if the following requirements had been met:
      1. (i)A proper and timely request for payment had been filed; and
      2. (ii)The hospital, CAH, SNF, or home health agency had submitted all necessary evidence, including physician or allowed practitioner certification of need for services when such certification was required;
   3. (3)They could not be paid for because the total payment due was equal to, or less than, the applicable deductible and coinsurance amounts.
2. (b)Exception. Even though the requirements of paragraph (a)(2) of this section are met, lifetime reserve days are not counted toward the allowable amounts if the beneficiary elected or is deemed to have elected not to use them as set forth in § 409.65.