Medicare Open Enrollment Dates and the Part B Mistake

Medicare open enrollment dates: October 15 to December 7

Medicare open enrollment runs October 15 through December 7 every year, and any change you make takes effect January 1. For the 2027 plan year, the window is October 15 to December 7, 2026.

Three readers land here, and they need different parts of this page:

Already enrolled and reviewing coverage — the next section lists what this window lets you change.
Turning 65 and not yet signed up — skip to “This is not the window for signing up for Part B.” Your deadline is a different one.
Helping a parent — the four-window table below identifies which period applies to them.

What you change here lands on more than one line item, because Medicare bills through five separate charges rather than a single premium.

ℹ️ Financial Disclaimer: This is general education about Medicare enrollment periods — not personalized advice on insurance, tax, credit, lending, or debt relief. Plan selection is an insurance decision with tax consequences through income-related premium adjustments. Before acting, consult a State Health Insurance Assistance Program counselor, a state-licensed insurance broker, or a CPA about the income side. Researched from primary CMS and Medicare.gov sources; AI tools assisted in drafting, and every figure was verified against the cited authority.

What you can actually change between October 15 and December 7

Between October 15 and December 7 you can do five things, and each one starts January 1:

Medicare Open Enrollment Dates and coverage changes for Medicare Advantage and Part D — During Medicare Open Enrollment, eligible beneficiaries can join, switch, or drop Medicare Advantage and Medicare drug coverage.

Join a Medicare Advantage plan for the first time.
Switch from one Medicare Advantage plan to another.
Leave Medicare Advantage and return to Original Medicare.
Join, switch, or drop a Part D prescription drug plan.
Add a standalone Part D plan alongside Original Medicare.

You can change your mind as often as you like inside the window. Only the choice on record at the December 7 cutoff counts.

What happens if you do nothing

Nothing lapses. Your plan renews into its next-year version, which can carry a different premium, a different covered-drug list, and a different provider network.

⚠️ Costly Mistake: Reading renewal as “no change.” The plan changes even when you don’t. A medication covered in 2026 can drop off the formulary for 2027, and you would find out at the pharmacy counter in January.

Medicare’s own breakdown of when you can join, switch or drop a plan covers the mechanics. If the switch itself is the question, start with how Medicare Advantage plans are built.

This is not the window for signing up for Part B

Medicare Open Enrollment Dates compared with the separate Part B enrollment periods — Medicare Open Enrollment is for changing health and drug plan coverage—not for using the annual October 15–December 7 window to enroll in Part B.

You cannot use October 15 to December 7 to enroll in Part A or Part B. This window only moves Medicare Advantage and Part D coverage, and only for people who already have Medicare.

When you actually sign up

Your Initial Enrollment Period is seven months: the three months before your 65th birthday month, that month, and the three months after. That is the signup deadline that matters if you are new to Medicare.

Two things legitimately delay it. Active employer coverage can, though the size of the employer decides the answer. COBRA generally does not — it is not treated as creditable coverage for Part B purposes.

If you already missed it

The General Enrollment Period runs January 1 to March 31. Coverage begins the first of the month after you enroll.

✅ Action Step: If you are past 65 and still working, put one question to your benefits administrator in writing: “Is our group plan creditable coverage for Medicare purposes, and does it qualify me for a Special Enrollment Period?” Then confirm your Part B start date directly with the Social Security Administration. The full list of qualifying situations is published by Medicare.

What using the wrong window actually costs

The Part B late enrollment penalty is 10% of the standard premium for each full 12-month period you could have signed up but didn’t, and it lasts as long as you have Part B.

🔍 How It Works: The penalty is a percentage, not a fixed dollar amount, so it is recalculated every year against that year’s standard premium. It does not expire, and it does not shrink.

The Part B penalty, calculated

The standard Part B premium is $202.90 per month in 2026, per Medicare.gov. A 12-month delay adds 10%:

$202.90 × 10% = $20.29 per month, or $243.48 per year — permanently.

Medicare’s own published example runs it further: a two-year delay is a 20% surcharge, bringing the 2026 monthly premium to $243.50. Over a 20-year retirement, that is roughly $9,700 in premiums for a deadline that was missed once. The full penalty mechanics sit in a separate guide.

The Part D penalty, calculated

Part D works differently: 1% of the national base beneficiary premium — $38.99 in 2026 — for every full month without creditable drug coverage, triggered once a gap reaches 63 days. The month-by-month math compounds quietly, and Medicare’s published penalty calculation shows both formulas side by side.

Four Medicare windows, and which one is yours

Four separate windows get called “open enrollment,” and they do different jobs.

Medicare Open Enrollment Dates compared with four Medicare enrollment windows — Different Medicare enrollment windows serve different purposes, from changing Medicare Advantage or Part D coverage to enrolling in Part A or Part B.

Window	Dates	Who it’s for	What it permits	Key detail
Annual Enrollment Period	Oct 15 – Dec 7	Anyone with Medicare	Change Medicare Advantage or Part D	Cannot be used to enroll in Part A or B
Medicare Advantage Open Enrollment	Jan 1 – Mar 31	Current Medicare Advantage enrollees only	One switch, or return to Original Medicare	Cannot be used to join Advantage from Original Medicare
General Enrollment Period	Jan 1 – Mar 31	People without Part A or Part B	Enroll in Part A and Part B	Coverage starts the first of the following month
Medigap Open Enrollment	Six months, once	Turning 65 and enrolled in Part B	Buy any Medigap policy sold in your state	Personal, not calendar-based; never repeats

Source: Centers for Medicare & Medicaid Services and Medicare.gov, verified September 2026.

One more exists: a 5-star Special Enrollment Period lets you move into a 5-star plan once between December 8 and November 30, if one serves your area. The six-month Medigap window and what it protects is the one most often confused with the annual period — it suspends medical underwriting, and it does not come back. Costs across all four windows roll up into what Medicare runs per year.

✅ Action Step: Ask a State Health Insurance Assistance Program counselor one question before you change anything: “Given my Part B start date and my current coverage, which window am I in right now, and what am I allowed to change?”

Most people don’t compare — and that’s where the money goes

Medicare Open Enrollment Dates and Medicare plan comparison of premiums medications doctors and networks — A smart Medicare plan review considers premiums, medications, doctors, provider networks, and overall annual costs—not just the monthly premium.

Skipping the review is the norm, not the exception.

📊 Data Point: 69% of Medicare beneficiaries did not compare their coverage against other options during an open enrollment period, and 43% of Medicare Advantage enrollees did not review their own plan for cost changes — Source: KFF analysis of the CMS Medicare Current Beneficiary Survey (2022 file, most recent available).

Two verified changes make the 2027 review worth more than usual. The Part D national base beneficiary premium rises to $41.33 from $38.99, a 6.0% increase and the maximum the Inflation Reduction Act permits — per the CMS bid announcement of July 28, 2026. In the same release, CMS confirmed the Part D Premium Stabilization Demonstration ends after 2026, returning standalone drug plans to ordinary market pricing.

The 2027 standard Part B premium has not been announced. CMS publishes it in mid-November, so check then rather than trusting a projection — the current Part B premium is the only confirmed figure until it lands. Higher earners should also review the income thresholds that raise both premiums and the Part D out-of-pocket cap.

Five mistakes that cost money in this window

These are the errors this article has been correcting, gathered in one place.

Ignoring the Annual Notice of Change, which your plan must send by September 30.
Comparing on monthly premium alone instead of total annual cost with your actual medications.
Assuming this window lets you enroll in Part B.
Assuming the January window lets you join Medicare Advantage from Original Medicare.
Dropping a Medigap policy to try Medicare Advantage.

⚠️ Costly Mistake: The Medigap exit is close to one-way. Once your six-month window has passed, insurers can apply medical underwriting, which means your health history can raise the price or block the policy entirely.

Where to get free help

Your state offers free one-on-one counseling through the State Health Insurance Assistance Program, and 1-800-MEDICARE answers plan questions at no cost. Neither earns a commission on what you choose.

Medicare open enrollment: common questions

1. When does Medicare open enrollment start and end?

Medicare open enrollment dates are October 15 through December 7 every year, with any changes taking effect January 1.

2. When does coverage from open enrollment begin? J

anuary 1 of the following year, whether you enrolled on October 15 or on December 7.

3. What can I change during Medicare open enrollment?

You can join, switch, or drop a Medicare Advantage or Part D plan, or return to Original Medicare. Confirm plan details with a SHIP counselor before switching.

4. Do I have to do anything if I like my current plan?

No. Your plan renews automatically, but its premium, drug list, and provider network can all change for the new year.

5. Can I sign up for Part B during open enrollment?

No. This window changes Medicare Advantage and Part D only; Part B signup happens during your Initial or General Enrollment Period. Confirm your dates with the Social Security Administration.

6. How much is the Part B late enrollment penalty?

Ten percent of the standard premium for each full 12-month period you delayed, added permanently to your monthly premium. Ask the Social Security Administration whether a penalty applies to you.

7. How much is the Part D late enrollment penalty?

One percent of the national base beneficiary premium for each full month you went without creditable drug coverage, charged permanently. A SHIP counselor can confirm whether your past coverage counted.

8. What’s the difference between this and Medicare Advantage Open Enrollment?

Open enrollment is available to everyone on Medicare; the January 1 to March 31 window serves only people already in a Medicare Advantage plan.

9. What happens if I miss the December 7 deadline?

Your current coverage continues into the new year, and your next opportunity depends on which window your situation qualifies you for.

10. Can I buy a Medigap policy during open enrollment?

You can apply, but your protected six-month Medigap window is personal and one-time — it is not this annual period. A licensed broker can tell you whether underwriting applies.

11. Where can I get free help comparing Medicare plans?

Your State Health Insurance Assistance Program provides free one-on-one counseling, and 1-800-MEDICARE answers plan questions at no cost.

Before December 7

Pull your Annual Notice of Change, then run your actual medication list and your doctors through the Medicare Plan Finder — premium alone will mislead you. If anything is unclear, book a free SHIP appointment while the calendar is still open. Then fold both premiums into your fixed monthly costs using the retirement income calculator.

Written byView profile

Sameer Patel — Founder & Editor

Research, drafting and original analysis

Contributor at Finance Authority Hub.

Important notice

Informational disclaimer

The content on Finance Authority Hub is provided for general informational and educational purposes only and should not be considered personalized financial, investment, tax, legal, or professional advice. Financial decisions depend on your individual goals, income, risk tolerance, location, and regulatory situation. Before acting on any information, strategy, estimate, or calculator result, consult a qualified licensed professional who can evaluate your specific circumstances.

Medicare open enrollment dates and the window people overlook

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Medicare open enrollment dates: October 15 to December 7