42 CFR § 406.21 - Individual enrollment.
(a) Basic provision. An individual who meets the requirements of § 406.20 (b) or (c) may enroll for premium hospital insurance only during his or her “initial enrollment period”, a “general enrollment period”, a “special enrollment period”, or, for HMO/CMP enrollees, a “transfer enrollment period”, as set forth in paragraphs (b) through (f) of this section.
(b) Initial enrollment periods -
(1) Initial enrollment period for individual age 65 or over. The initial enrollment period extends for 7 months, from the third month before the month the individual first meets the requirements of § 406.20 (b)(1) through (b)(3) through the third month after that first month of eligibility.
(2) Initial enrollment period of individual under age 65. The initial enrollment period begins with the month in which the individual receives notice that entitlement to Medicare Part A will end because he or she has lost entitlement to disability benefits solely because of earnings in excess of the amounts allowed under the social security regulations on substantial gainful activity (20 CFR 404.1571-404.1574). It continues for 7 full months after that month.
(c) General enrollment period.
(1) Except as specified in paragraph (c)(4) of this section, the general enrollment period extends from January 1 to March 31 of each calendar year.
(2) General enrollment periods are for individuals who do not enroll during the special enrollment period, who failed to enroll during the initial enrollment period, or whose previous period of entitlement had terminated.
(3) If the individual enrolls or reenrolls during a general enrollment period, his or her entitlement begins on July 1 of the calendar year.
(4) During the period April 1 through September 30, 1981, the general enrollment period was any time after the end of the individual's initial enrollment period. Any eligible individual whose initial enrollment period has ended, or whose previous period of entitlement had terminated, could enroll or reenroll during that 6-month period.
(d) “Deemed” initial enrollment period for individual age 65 or over.
(1) If an individual who has attained age 65 fails to enroll during the initial enrollment period because of reliance on incorrect documentary information which led him or her to believe that he or she was not yet age 65, an initial enrollment period may be established for him or her as though he or she had attained age 65 on the date indicated by the incorrect documentary information.
(2) The deemed initial enrollment period will be used to determine the individual's premium and right to enroll in a general enrollment period if such use is advantageous to the individual.
(f) Transfer enrollment period for HMO/CMP enrollees -
(2) Basic rule. Effective February 1, 1991, individuals enrolled in an HMO or CMP under part 417, subpart K of this chapter who meet the requirements of § 406.20(b) may enroll in premium hospital insurance during a transfer enrollment period. This transfer enrollment period begins with any month or any part of a month in which the individual is enrolled in an HMO or CMP and ends with the last day of the 8th consecutive month in which the individual is no longer enrolled in the HMO or CMP.
(3) Effective date of coverage.
(i) If the individual enrolls in premium hospital insurance while still enrolled in an HMO or CMP, or during the first month that he or she is no longer enrolled in the HMO or CMP, part A coverage will begin on the first day of the month of part A enrollment, or, at the option of the individual, on the first day of any of the following 3 months.
(ii) If the individual enrolls in premium hospital insurance during any of the last 7 months of the transfer enrollment period, coverage will begin on the first day of the month after the month of enrollment.