Medicare requires that nearly all workers sign up for the program during a seven-month Initial Enrollment Period (IEP) that includes the three months before, the month of, and the three months following their 65th birthday. If you are already receiving Social Security at that point, you will be signed up for Medicare Part A (hospitalization) and Part B (outpatient services) automatically.

But everyone else needs to pay careful attention to the enrollment rules. Missing your IEP can trigger late-enrollment penalties levied in the form of higher premiums that continue for life.

There really is only one important exception to the enrollment mandate. You can postpone enrollment if you are still working beyond age 65 and have insurance through your employer, or if you receive insurance through your spouse’s employer. (One exception to that exception: if you work for an employer with fewer than 20 workers, you can continue with that coverage, but Medicare becomes your primary source of insurance at age 65, and you should sign up during your IEP.

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