Initial Enrollment Period 7 Months

Medicare’s Initial Enrollment Period is seven months: three before your 65 birthday month, your birthday month, and three after — and the Medigap clock inside it matters as much as the Medicare one.

Window	Months	What Happens
Before 65	Months 1–3 pre-birthday	Part B can start on birthday month
Birthday month	Month 4	Part B effective; Medigap OEP can begin
After 65	Months 5–7	Last chance to avoid Part B late penalty

Sequencing Part B and Medigap

Medigap’s own guaranteed-acceptance window (the six-month OEP) starts when you are 65 AND enrolled in Part B — binding both together is the clean path. The penalty mechanics for missing Part B are in the late-enrollment file.

Working past 65

With employer coverage, IEP can be deferred — but the rules differ for companies under/over 20 employees, and COBRA timing traps are common. The interplay with guaranteed-issue rights when employer coverage ends is worth reading before giving notice.

FAQ

When should I apply for Part B?

Two-to-three months before you want coverage active; the SSA application can be filed up to 3 months pre-eligibility.

Does the IEP apply to Medicare Advantage too?

Yes — the same 7-month window opens MA enrollment.

Related reading: All windows · Medigap OEP · Part B penalty