Medicare Enrollment Basics

Medicare is the federal health insurance program for people 65 and older, and enrolling at the right time matters: missing your window can mean permanent premium penalties and coverage gaps.

The parts of Medicare

• Part A — hospital insurance; premium-free for most people with a sufficient work history.
• Part B — outpatient and doctor services; monthly premium, income-adjusted (IRMAA).
• Part C (Medicare Advantage) — private all-in-one plans replacing A/B delivery, often with drug coverage.
• Part D — prescription drug coverage through private plans.
• Medigap — private supplemental policies that fill cost-sharing gaps in Original Medicare.

Your initial enrollment period

The Initial Enrollment Period (IEP) is seven months: the three months before your 65th-birthday month, that month, and the three months after. Enrolling early in the window prevents coverage delays.

Still working at 65?

If you (or your spouse) have coverage from an employer with 20 or more employees, you can usually delay Part B without penalty and use a Special Enrollment Period when that employment ends. Two important traps:

• COBRA and retiree coverage do not count as active employer coverage for penalty purposes.
• HSA contributions must stop before Medicare enrollment begins — and Part A can be backdated up to six months when you enroll late, which catches many HSA contributors off guard.

Penalties for late enrollment

• Part B: premiums rise 10% for each full 12-month period you were eligible but not enrolled — for life.
• Part D: a smaller but also permanent penalty accrues for each month without creditable drug coverage.

The Medigap window

Your one guaranteed-issue window for Medigap is the six months after Part B starts. After it closes, insurers in most states can deny coverage or charge more based on health.

Key takeaways

• Mark the seven-month window around your 65th birthday.
• Working past 65 can justify delaying Part B — but only with qualifying employer coverage, and mind the HSA rules.
• Part B, Part D, and Medigap each have deadlines with lasting consequences.

This article is for educational purposes only and is not insurance advice. Consult your advisor about your specific situation.