Missing the right window can mean late penalties, coverage gaps, or being locked out of the plan you want. Here’s every enrollment period, when it applies, and what you can do during each one.
This is your first and most important enrollment window. It runs for 3 months before the month you turn 65, the month of your birthday, and 3 months after — 7 months total.
What you can do: Enroll in Part A, Part B, a Part D drug plan, and a Medigap plan. This is your guaranteed issue window for Medigap — no health questions, no underwriting.
When coverage starts: If you enroll in the 3 months before your birthday month, coverage starts on the first day of your birthday month. If you enroll in your birthday month or after, coverage starts 1–3 months later.
Don’t miss this window. Enrolling late in Part B triggers a permanent 10% premium increase for each 12-month period you were eligible but didn’t enroll. Late Part D enrollment carries its own penalty. These surcharges never go away.
Use the official 2026 figures to estimate your Part B and Part D late penalties. Both are permanent, so the calculator also shows the long-term cost.
The Part B penalty adds 10% of the standard premium ($202.90 in 2026) for each full 12-month period you were eligible but didn't enroll (without other job-based coverage).
Optional: fill these to auto-calculate your months late, or just type the number below.
$0.00
Estimated monthly penalty added to your Part B premium
Enter your months above to see your estimated penalty.
The Part D penalty adds 1% of the national base premium ($38.99 in 2026) for every full month you went without Part D or other creditable drug coverage (a gap of 63+ days).
Optional: fill these to auto-calculate your uncovered months, or just type the number below.
$0.00
Estimated monthly penalty added to your Part D premium
Enter your months above to see your estimated penalty.
If you or your spouse are still working and covered by employer insurance when you turn 65, you can delay Medicare enrollment without penalty and enroll later during a Special Enrollment Period when that coverage ends.
SEP for employer coverage: You have 8 months from when your employer coverage ends (or you stop working, whichever comes first) to enroll in Part B without penalty.
Other SEP triggers include: Moving to a new area, losing Medicaid eligibility, leaving a Medicare Advantage plan that leaves your area, and other qualifying events.
This is your guaranteed right to buy any Medigap plan in your state without medical underwriting. It starts the month you’re both 65+ and enrolled in Part B, and lasts 6 months.
This window does not repeat. After it closes, switching Medigap plans in most states requires answering health questions and can result in denial or higher premiums.
Missouri exception: Missouri’s Anniversary Rule gives you an annual window to switch Medigap carriers without underwriting — but this is for switching between carriers, not for initial enrollment after your open enrollment window closes.
Every fall, you can make changes to your Medicare Advantage or Part D plan. Changes take effect January 1 of the following year.
What you can do: Switch Medicare Advantage plans, switch Part D plans, join or drop a Medicare Advantage plan, or switch between Original Medicare and Medicare Advantage.
Important: AEP does NOT give you guaranteed issue rights for Medigap. If you want to switch from Medicare Advantage to a Medigap plan, you may face underwriting in most states (except Missouri’s Anniversary Rule window, which is separate).
If you’re enrolled in a Medicare Advantage plan, you can switch to a different MA plan or return to Original Medicare (and add a standalone Part D plan) during this window.
You cannot use this period to enroll in a Medigap plan with guaranteed issue rights — that still requires underwriting in most states.
Not sure which enrollment window applies to your situation? We’ll tell you exactly what your options are and what deadlines you need to hit.
Book a Free Review