You need to sign up for Part B at certain times, or you may have to pay a penalty for the rest of your life. If you’re already receiving Social Security retirement benefits, you’ll be enrolled automatically in Medicare parts A and B at the beginning of the month you turn 65 or, if your birthday is on the first day of a month, during the previous month. (Puerto Rico’s rules differ.)
If you don’t have other insurance, you usually need to sign up for Part B when you are first eligible for Medicare, which is during the seven-month initial enrollment period that runs from three months before to three months after the month you turn 65.
If you or your spouse are still working and you have coverage through that employer’s plan, you may be able to delay signing up for Part B. But you must enroll within eight months of losing that employer-based coverage to avoid a penalty.
Be aware: If the company you are working for has fewer than 20 employees, you generally should sign up for Medicare parts A and B at age 65. Otherwise, you may have gaps in coverage.
If you miss those deadlines, you may have to pay a late enrollment penalty of 10 percent for each 12-month period you could have had Part B but didn’t sign up. The penalty is added to your monthly premium for as long as you have Part B.