Medicare Annual Enrollment: The 5 Deadlines That Matter

If you take one thing from this article: the only deadline that can permanently raise what you pay is the one around your 65th birthday. The rest, including important Medicare deadlines such as Annual Enrollment, are recoverable. Here they are in the order they’ll matter to you.

1. Your Initial Enrollment Period — seven months around your 65th birthday

It opens three months before the month you turn 65, includes your birthday month, and closes three months after. Enroll in Part A and Part B in this window and there’s no penalty and no gap. Sign up in the three months before your birthday month and coverage starts the first day of your birthday month.

The exception that trips people up: if you’re still working and covered by a qualifying employer group health plan, you may be able to delay Part B safely. Whether that’s true depends on how many employees the company has and how the plan is structured — confirm it before your birthday, not after.

2. Your six-month Medigap open enrollment

This is the most valuable window in Medicare, and almost nobody mentions it. For six months starting when your Part B takes effect, you can buy any Medicare Supplement policy sold in your state with no health questions asked. After it closes, most states let insurers underwrite — meaning they can charge more or decline you.

3. Annual Enrollment — October 15 to December 7

Every year, this is your dependable chance to change Medicare Advantage or Part D plans. Whatever you choose takes effect January 1. It’s also the right moment to re-price your prescriptions, because formularies change every January — a plan that was cheapest last year often isn’t.

Miss it and you generally keep what you have for another year, unless you qualify for a Special Enrollment Period. Inconvenient, not permanent.

4. Medicare Advantage Open Enrollment — January 1 to March 31

If you’re already in a Medicare Advantage plan and January makes it obvious the plan doesn’t fit, you get one change during these three months: switch to another Advantage plan or return to Original Medicare. One change, not several.

A caution: returning to Original Medicare doesn’t guarantee you can buy a Medigap policy. Outside a guaranteed-issue right, that purchase may require underwriting.

5. The 63-day drug coverage rule

Go 63 days or more without Part D or other creditable prescription coverage after you’re eligible, and a late enrollment penalty is added to your Part D premium — roughly 1% of the national base premium for every month you went without, for as long as you have Part D coverage.

This is why people who take no medications still buy a minimum-premium plan. It’s inexpensive insurance against both a new prescription and a permanent surcharge. Coverage through the VA, TRICARE, or a retiree plan usually counts as creditable — but get that in writing.

What about all the other deadlines you’re hearing about?

If a postcard or a phone call is pressuring you toward a date that isn’t one of the five above, treat it as marketing. Real Medicare deadlines are published by CMS and don’t depend on calling a particular number today.

Special Enrollment Periods are the genuine exception to all of this. Losing employer coverage, moving to a new service area, gaining Medicaid or Extra Help, or a plan leaving your county can each open a window outside the normal calendar. If your life changed, ask — you may have more options than you think.

What you can actually change during Annual Enrollment

Annual Enrollment is the one window each year that is open to everybody on Medicare, whatever your circumstances. Between October 15 and December 7 you can do any of the following, and you may do more than one.

• Move from Original Medicare to a Medicare Advantage plan.
• Move from Medicare Advantage back to Original Medicare.
• Switch from one Medicare Advantage plan to another.
• Join a Part D drug plan, change to a different one, or drop it.

What Annual Enrollment does not hand you is a guaranteed right to buy a Medigap policy. That is a separate matter governed by your state’s rules, and it is the most common misunderstanding about the Annual Enrollment period.

Your Annual Enrollment checklist

Most people who lose money during Annual Enrollment do so by doing nothing. Carriers may change premiums, deductibles, copays, drug formularies and provider networks every January, and the plan that was cheapest for you last year often is not this year.

Read the Annual Notice of Change. Your carrier must send it by September 30, ahead of Annual Enrollment opening. It lists every change to your plan for the coming year in one document. It is dull, and it is the most valuable post you will receive all year.

Re-price your prescriptions. Put your real drug list, with doses, into Medicare’s Plan Compare tool. Formulary tiers move, and one drug changing tier can swing your annual cost by hundreds of dollars.

Confirm your doctors are still in network. Networks are refreshed for January. A physician who was in network in December may not be in January, and Annual Enrollment is your chance to respond to that.

Look at the out-of-pocket maximum, not the premium. On a Medicare Advantage plan, the annual out-of-pocket ceiling is what protects you in a bad year. The premium is what you notice; the ceiling is what matters.

Decide before December 7. The date is firm. Changes made during Annual Enrollment take effect January 1, and the last election you make is the one that counts.

Annual Enrollment is not the same as Open Enrollment

The two names get used interchangeably and they should not be. Annual Enrollment runs October 15 to December 7 and is open to everyone on Medicare. Medicare Advantage Open Enrollment runs January 1 to March 31, is open only to people already in an Advantage plan, and allows one change.

There is also the Health Insurance Marketplace open enrollment, which has nothing to do with Medicare but sits close enough on the calendar to confuse people every year. If you are on Medicare, the Marketplace is not where you shop.

Pressure tactics during Annual Enrollment

Annual Enrollment is the busiest marketing season in American health insurance, and the volume of calls, postcards and television advertising rises to match. A few rules protect you.

An agent may not cold-call you without permission, may not turn up at your door uninvited, and may not offer you a gift beyond a nominal value to enrol. Before discussing specific plans, an agent must have a Scope of Appointment recorded, and may only cover the product lines you agreed to.

Nobody from Medicare will telephone you during Annual Enrollment to ask for your Medicare number, your bank details or your Social Security number. If a caller does, hang up and report it to 1-800-MEDICARE.

And no legitimate deadline expires today. If a caller tells you it does, that is a sales technique, not a fact.

If you miss Annual Enrollment

Missing Annual Enrollment is inconvenient rather than permanent. You keep your current plan for another year unless a Special Enrollment Period opens for you.

Those are more common than people expect. Moving out of a plan’s service area, losing employer coverage, entering or leaving a nursing home, qualifying for Medicaid or Extra Help, or your plan withdrawing from your county each open a window outside Annual Enrollment. If your circumstances have changed, ask.

Free help during Annual Enrollment

You never have to pay for help with this. Every state runs a State Health Insurance Assistance Program staffed by trained counsellors who sell nothing at all.

• Medicare.gov Plan Compare — every plan in your ZIP code with your prescriptions priced in
• SHIP National Technical Assistance Center — find your state’s free Medicare counselling service
• Social Security Administration — Extra Help with prescription drug costs
• CMS annual calendar — the official dates, published by the agency that sets them

If you would rather talk it through with a licensed agent who can see every plan in your area, O’Neal Insurance Group is on (877) 808-2900. Our help during Annual Enrollment costs you nothing — agents are paid by the carrier, not by you.

Related guides on this site

• Medicare Simplified — the full beginner’s guide, start to finish
• What Medicare Advantage costs — premiums, copays and the out-of-pocket ceiling
• How Medigap works — and why its own window matters more than Annual Enrollment
• Book a no-cost appointment before December 7

This article is general information, not advice about your specific situation, and figures reflect the 2026 plan year. For official information, see Medicare.gov’s enrollment pages or call 1-800-MEDICARE.