Medicare 101 Series
Medicare · Enrollment Windows
Every Window You Can —
and Can't — Use
Medicare has six different enrollment windows. Each one lets you do different things, lasts different lengths of time, and most have a lifetime penalty if you miss them. Knowing which window you're in matters more than people realize.
Part D late-enrollment penalty
Skip Part D when first eligible and the penalty compounds every month you go without — for the rest of your life. The same math applies to Part B.
The Medicare Year at a Glance
Fixed-date windows across the calendar year. IEP, Medigap OE, and SEPs aren't shown because they depend on personal triggers (your birthday, Part B effective date, life events).
IEP
Initial Enrollment Period
7 months around your 65th birthday
Medigap OE
Medigap Open Enrollment
6 months from when Part B becomes effective
SEPs
Special Enrollment Periods
Triggered by qualifying life events (move, lose coverage, etc.)
Initial Enrollment Period
7 months: 3 before, the month of, and 3 after your 65th birthday
First time enrolling in Medicare. Sign up for Part A, Part B, Part D, or a Medicare Advantage plan.
Consequence
Miss it → lifetime late-enrollment penalty for Part B and Part D.
Medigap Open Enrollment
6 months starting the month your Part B becomes effective
The ONLY guaranteed window to buy ANY Medicare Supplement (Medigap) plan without health questions. After this, you can be denied or charged more for pre-existing conditions.
Consequence
Miss it → underwriting required. Health issues can mean denial or higher premiums.
Annual Enrollment Period
October 15 – December 7 every year
The main annual switch window. Change Medicare Advantage plans, switch between Original Medicare + Part D and Medicare Advantage, or change Part D plans. Changes take effect January 1.
Consequence
Most people who want to change plans must do it in this window or wait a year.
Medicare Advantage OEP
January 1 – March 31 every year
If you're on a Medicare Advantage plan, you can make ONE change during this window: switch to a different MA plan, or drop MA and return to Original Medicare (with a Part D plan).
Consequence
Only applies if you're already enrolled in a Medicare Advantage plan.
General Enrollment Period
January 1 – March 31 every year
For people who missed their Initial Enrollment Period and don't qualify for a Special Enrollment Period. You can enroll in Part B (and Part A if not premium-free).
Consequence
Late-enrollment penalties usually apply. Coverage starts the month after you sign up.
Special Enrollment Periods
Triggered by qualifying life events — varies
Examples: you move out of your plan's service area, lose employer coverage, qualify for Extra Help, your plan stops serving Medicare, or a 5-Star plan becomes available in your area.
Consequence
Window length depends on the event (usually 2 months). Document the trigger event for proof.
The annual rhythm
Jan – Mar
MA OEP (one switch if you're on MA) + GEP (for late enrollees)
Apr – Sep
Quiet for most. SEPs still available if you have a qualifying event.
Oct 15 – Dec 7
AEP. The big annual window. Most plan changes happen here, effective January 1.
Not sure which window applies to you?
We'll look at your situation and tell you exactly which windows you can use right now — and which ones you should be watching for.
Keep Reading
More in Medicare
Sources
medicare.gov/sign-up · cms.gov
Educational content only. Not financial advice. Consult a licensed advisor for your specific situation.