Enrollment
Medicare enrollment: which window applies to you
There is more than one enrollment period, and they do different things. Here is which one you are in.
Initial Enrollment Period
Your seven-month window around your 65th birthday: three months before, your birthday month, and three months after. This is when most people first enroll in Part A and Part B.
Annual Enrollment Period, October 15 to December 7
The one most people mean by open enrollment. During this window you can join, switch, or drop a Medicare Advantage plan or a Part D drug plan. Changes take effect January 1.
This is the window to check your drug plan. Formularies, pharmacy networks, and costs change every year, and a plan that fit last year may not fit this year.
Medicare Advantage Open Enrollment, January 1 to March 31
If you are already in a Medicare Advantage plan, you get one chance in this window to switch to a different Advantage plan or to go back to Original Medicare and add a drug plan.
You cannot use this window to join an Advantage plan from Original Medicare.
General Enrollment Period, January 1 to March 31
For people who missed their initial window and do not qualify for a special one. Coverage generally begins the month after you sign up, and a late penalty may apply.
Special Enrollment Periods
Life events can open a window outside the usual dates. Common ones include moving out of your plan service area, losing employer or union coverage, leaving or entering a nursing facility, and qualifying for Medicaid or Extra Help.
People with both Medicare and Medicaid, and people who qualify for Extra Help, often have more chances to change plans during the year than everyone else.
Official resource
A rule that changed, and advice that is now wrong
The General Enrollment Period runs January 1 to March 31 for anyone who missed their initial Medicare enrollment window. It used to be that coverage bought during it did not start until July 1, leaving people uninsured for months after they had signed up and started paying.
That changed. Coverage now begins on the first day of the month after you enroll. Any guide or forum post still describing a July start date is working from superseded rules, and the difference can be six months of coverage.
It is worth knowing which Medicare enrollment advice ages badly, because a great deal of what circulates online was accurate when written and is not now. Anything about the coverage gap in Part D, the July start date, or year-round sign-up for lower-income households falls into that category.
The Medicare enrollment window most people never hear about
If a plan in your area holds five stars from CMS, you may switch to it once between December 8 and November 30 — almost the entire year, outside every other window.
Two conditions apply. The rating must be current, and ratings reset every autumn, so a plan that was five stars last year may not be. And it is one use per year, not a standing right to move around.
Five-star plans are uncommon and not evenly distributed, so this is worth checking rather than assuming. It is also the only Medicare enrollment route that rewards you for the plan’s quality rather than your circumstances.
Special Medicare enrollment periods, and what you will be asked to prove
Most special Medicare enrollment windows run 60 days from the qualifying event. The ones that come up most often, and the document that usually settles each:
- You moved out of your plan’s service area, or somewhere with different plans available. A lease, deed or utility bill.
- You lost other coverage — employer plan ending, COBRA running out, losing Medicaid. The termination letter, which is the document people throw away.
- You gained, lost or changed Medicaid or Extra Help. The award or termination notice.
- Your plan is leaving Medicare or your county. The non-renewal notice, which arrives in autumn among a great deal of marketing post.
- You moved into, live in, or left a nursing facility. Admission or discharge paperwork.
- You were misled or the plan broke the rules. Whatever record you have of it.
One route has closed. The monthly Special Enrollment Period for households under 150 percent of the federal poverty level was removed in 2025. If you have been told you can sign up any month because your income is low, that guidance is out of date.
The two one-time rights attached to Medicare enrollment
These are not enrollment periods in the usual sense, but they are deadlines, and missing them is permanent.
If you joined a Medicare Advantage plan when you first became eligible for Part A at 65, and you leave within twelve months, you may buy a Medicare Supplement with no health questions asked. Separately, if you already had a supplement, dropped it to try Advantage for the first time, and leave within twelve months, you may buy back in.
Both require you to apply no earlier than 60 days before the Advantage coverage ends and no later than 63 days after. Both are available once in a lifetime. Someone who tried Advantage years ago, went back, and is considering it again has no trial right left.
This is the part of Medicare enrollment that most rewards planning, because outside those windows a supplement application is medically underwritten and an insurer may decline you outright. A handful of states are more generous — Connecticut, New York, Massachusetts and Washington in particular — but Mississippi, Nevada and Illinois all follow the federal floor or close to it.
What a missed deadline actually costs
The Part B penalty adds 10 percent of the standard premium for every full 12-month period you could have had it and did not, and it lasts as long as you hold Part B. On the 2026 standard premium of $202.90, two years late is roughly $40 a month, every month, permanently.
The Part D penalty works differently: one percent of the national base beneficiary premium — $38.99 for 2026 — for each month without creditable coverage, recalculated annually and also permanent. Neither penalty can be appealed once correctly applied, which is what makes the calendar worth more attention than most of the plan comparison.
Check the source, then ask for personal help
Educational information is general. A licensed agent can help with plan comparisons; agents do not provide medical, legal, or official eligibility advice.
How to work out which Medicare enrollment window you are in
Almost everybody who calls us about Medicare enrollment is in one of five situations. Read down this list and stop at the first one that describes you.
You are turning 65 and not covered by a current employer. You are in your Initial Enrollment Period. It runs the three months before your birthday month, the birthday month itself, and the three months after. Sign up in the first three months and Part B starts the month you turn 65; sign up during or after your birthday month and it starts the following month.
You are turning 65 and still working, with group coverage from that job. You may be able to delay Part B without any penalty at all. Do not guess — the answer depends on how many employees the employer has, and getting it wrong is expensive in both directions.
You have Medicare already and want to change plans. You are looking at the Annual Enrollment Period from October 15 to December 7, and possibly the Medicare Advantage Open Enrollment Period from January 1 to March 31.
Something in your life has just changed. A move, a job loss, a nursing-home admission, a Medicaid approval. That is a Special Enrollment Period, and it does not wait for the calendar.
You missed your window and nothing above applies. That is the General Enrollment Period, January 1 to March 31, with coverage starting the month after you sign up.
Medicare enrollment when you are still working
This is where most costly errors happen, and the rule is not intuitive.
If you have group health coverage through current employment, you generally get a Special Enrollment Period of eight months to sign up for Part B without penalty. It begins when you or your spouse stop working, or when the job-based coverage ends — whichever comes first.
The trap is COBRA. The eight-month clock starts when the employment ends, even if you elect COBRA. COBRA does not pause it and neither does retiree coverage. People spend eighteen months on COBRA believing they are covered, then discover their Medicare enrollment window closed ten months earlier, and they wait until January with a penalty attached for life.
The safe pattern is to sign up for Part B the month before the job coverage ends, so the two overlap by nothing and gap by nothing.
The first week of October is the worst time to decide
Plan data for the coming year publishes on Medicare.gov in early October, roughly a fortnight before the Medicare enrollment window opens. In its first days it is not always correct.
Consumer advocates have documented the Plan Finder showing inflated costs for some drugs, different prices for the same drug on the same plan, wrong premiums for people receiving Extra Help, and formulary details that did not match the plan. When the provider directory was rebuilt for 2026, a doctor could appear in network at one address and out of network at another under the same plan.
CMS built a remedy for that last one. For 2026, someone who enrolled in a Medicare Advantage plan through the Plan Finder, with a start date between January 1 and December 1, and then found within their first three months that their preferred doctor was not in the network, can change plans by calling 1-800-MEDICARE. Ask whether it still applies to your plan year rather than assuming you are stuck — it is the sort of thing a Medicare enrollment conversation should surface and rarely does.
The practical rule is simple. Read the Annual Notice of Change your plan must send you by September 30, then run your comparison in the second half of October rather than the first, and confirm each doctor with the practice rather than the directory. There is time: the window runs to December 7, and a Medicare enrollment decision made on October 20 is no worse than one made on October 2, but it is far better informed.
What a missed Medicare enrollment costs
The penalties are permanent, which is what makes the timing worth taking seriously.
Part B. An extra 10% on your monthly premium for each full year you could have signed up and did not. It is usually charged for as long as you have Part B — that is, for the rest of your life.
Part D. 1% of the national base beneficiary premium for each month you went without creditable drug coverage — 12% for a year. It is added for as long as you have Medicare drug coverage, and it follows you when you switch plans.
Part A. Most people get Part A without a premium and cannot be penalised. If you do have to buy it, the penalty is 10%, charged for twice the number of years you delayed.
None of these are negotiable after the fact, and none of them are waived because nobody told you. That is the whole argument for treating Medicare enrollment as a dated task rather than something to sort out eventually.
What you actually do during Medicare enrollment
There are two separate steps and people routinely do only the first.
Step one: enroll in Original Medicare. Parts A and B come from the Social Security Administration, online at ssa.gov, by phone, or at a local office. If you already draw Social Security benefits you are usually enrolled automatically and your card arrives without you doing anything.
Step two: decide what goes on top. Original Medicare on its own has no drug coverage and no out-of-pocket limit. You then choose either a Medicare Advantage plan, or a Medicare Supplement policy paired with a standalone Part D plan. That decision is made with a private insurer, not with Social Security, and it is the part we help with at no cost to you.
Before you start either step, have your Medicare number, your exact prescription list with dosages, and the names of the doctors you want to keep. A Medicare enrollment application that stalls halfway through usually stalls for want of one of those three.
Medicare enrollment mistakes we see most
Assuming enrollment is automatic. It is automatic only if you are already receiving Social Security or Railroad Retirement benefits when you become eligible. Otherwise nothing happens until you act.
Skipping Part D because you take no medication. The penalty accrues monthly whether or not you need the coverage, and health changes. A cheap drug plan you never use is far cheaper than the penalty.
Letting a plan auto-renew without reading the notice. Every plan sends an Annual Notice of Change each autumn. Formularies, networks and costs move every year, and the plan that was right last year frequently is not.
Treating the Medicare Advantage Open Enrollment Period as a second chance to join one. It is not. If you are in Original Medicare on January 1, that window does not let you switch into an Advantage plan.
Canceling a Medigap policy before the replacement is approved. Outside a guaranteed-issue right, the new carrier can ask health questions and decline you. Nothing obliges them to take you back.
Check any of this independently
Every date and figure above is published by the government and free to verify.
- Medicare.gov — when you can sign up — every enrollment period and the employer-coverage rules
- Medicare.gov — avoiding late penalties — the exact penalty formulas quoted above
- SSA.gov — sign up for Medicare — where Part A and Part B enrollment actually happens
- SHIP National Technical Assistance Center — free one-to-one counseling in your state
- CMS — special enrollment period for incorrect Plan Finder provider information — the remedy described above
Related guides on this site
- New to Medicare and turning 65 — the Initial Enrollment Period in detail
- The five Medicare deadlines that matter — the autumn window and what you can change
- Medicare Advantage enrollment periods — the January-to-March window explained
- Part D prescription drug plans — where the late penalty applies
- Book a no-cost appointment
Or call (877) 808-2900. Tell us your birthday and whether you are still working, and we will tell you in two minutes which Medicare enrollment window you are in and what the deadline is.
Personal guidance · No additional fee