A general enrollment period from Oct 15 through Dec 7 of each year permits people 65 or over who failed to enroll or dropped their Part B Medicare coverage to sign up. Their coverage will begin Jan 1.

Generally, a 10 percent premium penalty will be added to the monthly premium for each year they could have enrolled but did not. However, if you are covered by an employer or union group health plan through you or your spouse's current or active employment, you may qualify for a special enrollment period.

If you meet the requirements for a special enrollment period, you do not have to wait for a general enrollment period or pay a premium penalty. You have an eight-month special enrollment period if you have group health plan coverage from current employment at the time you first became eligible for Medicare. This special enrollment period begins with the month employment ends or the month your group health plan coverage ends, whichever comes first.

If you enroll in Part B after this eight-month window, you may face a late enrollment penalty and will not be able to enroll in a Medicare Advantage plan until the next general enrollment period.