CMS Pub. 100-01, ch. 3, § 10.4

A benefit period is a period of time for measuring the use of hospital insurance benefits.

It is a period of consecutive days during which covered services furnished to a patient, up

to certain specified maximum amounts, may be paid for by the hospital insurance plan.

For example, a patient is eligible for 90 days of hospital care in a benefit period and 100

days of extended care services during the same benefit period. A patient may be eligible

for as many as l50 days of hospital care in a benefit period if he/she draws on his/her

lifetime reserve. As long as a person continues to be entitled to hospital insurance, there

is no limit on the number of benefit periods he/she may have. The term "benefit period"

is synonymous with spell of illness. Since the term "spell of illness" could connote a

single illness or a particular "spell" of sickness, the term benefit period is used in

communications with the public.