Common Medicare enrollment mistakes before the Dec 7 deadline

Medicare plans rewrite their own terms every year, whether or not anyone is paying attention. Premiums, deductibles, drug formularies, pharmacy tiers, provider networks and out-of-pocket maximums can all shift on January 1. A plan that was the cheapest option one winter can turn into one of the costliest the next. None of that requires the beneficiary to make a wrong move. It only requires a renewal notice to go unread.

Open enrollment runs from October 15 through December 7. During that window, most people on Medicare can switch plans, change prescription drug coverage or move between Original Medicare and Medicare Advantage, with no health questions asked. The window then closes on its own, and coverage rolls into the new year on the insurer's terms rather than the enrollee's.

The consequences are concrete. The wrong Part D plan can add hundreds of dollars a year in costs for the same set of prescriptions. A Medicare Advantage plan that has dropped a hospital system or a longtime specialist can cut off access to a doctor in the middle of treatment. Missing the deadline usually means waiting a full year for another chance to change coverage. With Part B, enrolling late without qualifying coverage elsewhere can attach a permanent penalty to a monthly premium.

What follows are 10 Medicare open enrollment mistakes that surface year after year. They range from ignoring the Annual Notice of Change that arrives each fall to misunderstanding which enrollment window actually applies. None are hard to fix. Most come down to an hour with Medicare's official plan finder or a call to a doctor's office to confirm network status. Free counseling is another option: the State Health Insurance Assistance Program, known as SHIP, operates in every state. The aim here is not to point anyone toward a particular plan, since the right choice depends on health needs, prescriptions and budget. It is to name the recurring, avoidable missteps that leave people overpaying, cut off from their own doctors or stuck for 12 months with coverage that no longer fits.

Illustration: Quartz

The most common Medicare open enrollment mistake is doing nothing. Automatic renewal keeps a plan in force, but it does not preserve the terms that made the plan worth choosing. Every Medicare Advantage and Part D plan can revise its premium, deductible, cost-sharing, drug list and provider network for the coming year.

Those revisions are spelled out in the Annual Notice of Change, which plans send to current members each fall before enrollment opens on October 15. Inside are the details that determine whether the plan still fits: drugs added to or dropped from the formulary, medications moved between cost-sharing tiers, a new out-of-pocket maximum, and pharmacies or providers leaving the network.

A plan can keep its name and still work differently in January. A deductible can rise. A maintenance medication can shift to a higher tier and cost several times more per fill. A preferred pharmacy can become a standard one, which raises the copay at the counter without anything changing on the member's ID card.

Reading the notice establishes the baseline for every other decision. The second step is measuring that baseline against one or two alternatives on Medicare's official plan finder at medicare.gov, which lists every Medicare Advantage and Part D plan sold in a given ZIP code. The comparison is worth running even for people satisfied with their current coverage, because that satisfaction reflects this year's terms rather than next year's.

Plans also exit markets or merge. When a Medicare Advantage or Part D plan is discontinued in a service area, members are notified and need to select new coverage, and those who do not act can end up back in Original Medicare with no drug plan attached. Finding that out in October leaves weeks to choose deliberately instead of defaulting into whatever comes next.

Treating open enrollment as an annual review, rather than a decision made once and left alone, is the difference between seeing a cost increase in advance and discovering it in January, when a claim is denied or a refill costs more than expected.

Illustration: Quartz

A drug covered by a Part D or Medicare Advantage plan this year is not guaranteed to be covered next year, or covered at the same price. Formularies are rewritten annually, and checking next year's list directly is the only way to know what a prescription will cost in January.

Plans sort covered medications into tiers, and a drug can move from a lower, cheaper tier to a higher one while remaining on the formulary. That reclassification alone can raise a monthly copay substantially. A medication can also be dropped outright. That leaves two options: switch to an alternative the plan covers, or file a formulary exception request and wait for a decision.

Plans can also attach prior authorization requirements, step therapy rules or quantity limits to a drug that had none before. Those restrictions create delays at the pharmacy counter even when the drug stays covered.

Specialty medications carry the most exposure. The gap between how one plan treats a given drug and how another treats it can be large enough to reshape a year's budget. Anyone taking several maintenance prescriptions faces the same risk multiplied. One unfavorable tier change on each of four or five drugs adds up fast.

The practical step is to enter every current prescription into Medicare's plan comparison tool, including the exact dosage and the frequency. Then review the results against the plans on offer for the coming year rather than relying on this year's experience. Dosage matters, since quantity limits and tier placement can differ between strengths of the same medication.

Pharmacists can pull formulary information and flag coverage gaps, and many will do so during a routine refill in the weeks before December 7.

Generic drugs deserve the same check as brand-name ones. A low price this year does not exempt a generic from being dropped, repriced or moved to a different tier under the next plan year's rules.

Illustration: Quartz

The monthly premium is the most visible number in a Medicare plan comparison and one of the weakest predictors of what a year of coverage actually costs. A low-premium plan can carry a higher deductible, steeper specialist copays and coinsurance on expensive drugs. Any one of those can wipe out the monthly savings in a single round of care.

Annual cost comes from the full structure: premium, deductible, copayments or coinsurance and the ceiling on out-of-pocket spending. Medicare Advantage plans are required to cap in-network out-of-pocket costs for Part A and Part B services, and that cap varies widely from plan to plan. Part D now carries an annual limit on what a beneficiary pays out of pocket for covered prescriptions. That limit took effect in 2025 and is adjusted each year. Two plans with nearly identical premiums can sit thousands of dollars apart on those ceilings.

Medicare's plan finder is built for this calculation. Enter current prescriptions and a preferred pharmacy and the tool returns an estimated total annual cost, then ranks plans on that estimate rather than on the premium alone. Someone anticipating a knee replacement, a course of physical therapy or regular infusions should weigh that estimate far more heavily than the figure printed at the top of a plan summary.

Zero-premium Medicare Advantage plans deserve the same scrutiny. A $0 monthly premium is not free coverage. Enrollees still owe the standard Part B premium, and they still face copays for office visits, imaging, outpatient procedures and each hospital day. The per-service charges are where the money goes.

The right comparison depends on expected use. A person taking no regular medications, seeing a primary care doctor once a year and managing no chronic conditions may do fine with the cheapest premium on offer. Low expected use keeps the cost-sharing mostly theoretical. Someone managing diabetes, heart disease or cancer, or newly referred to a specialist for ongoing follow-up, often comes out ahead with richer coverage that costs more each month. Running the full-year estimate takes a few minutes and separates a plan that looks cheap from one that is.

Illustration: Quartz

Medicare runs several enrollment windows with different rules, and treating them as interchangeable is how people end up locked into a plan for a year or paying a penalty for life. The fall open enrollment period, October 15 through December 7, is the broad one: any change made during it takes effect January 1.

The window that follows it is narrower than most people expect. The Medicare Advantage Open Enrollment Period runs January 1 through March 31 and is available only to those already enrolled in a Medicare Advantage plan. It allows one switch to a different Medicare Advantage plan or a return to Original Medicare with a stand-alone Part D plan. Someone on Original Medicare in January cannot use it to join a Medicare Advantage plan. Nor can it be used to change a stand-alone Part D plan while staying on Original Medicare.

The Initial Enrollment Period is separate again. It spans seven months, beginning three months before the month someone turns 65, including the birthday month, and ending three months after. Special Enrollment Periods sit outside the calendar entirely. They are triggered by specific events such as losing employer group coverage, moving out of a plan's service area, or entering a nursing facility.

The penalty math is where confusion gets expensive. Delaying Part B past the Initial Enrollment Period without qualifying coverage from an employer adds 10% to the monthly premium for every full 12-month period of delay. That surcharge lasts for as long as the person holds Part B. Going without creditable prescription drug coverage carries its own Part D late enrollment penalty, which is also added to the premium permanently in most cases.

Anyone who assumes a plan choice can be fixed in February should confirm which window actually applies before December 7 passes. Writing both the October 15 start date and the December 7 cutoff on a calendar is more reliable than a general sense that Medicare enrollment happens sometime in the fall. For someone on Original Medicare with a stand-alone drug plan, the fall window is the only chance all year to change that drug coverage without a qualifying life event.

Illustration: Quartz

Medicare Advantage networks are rebuilt every year. A plan can drop a hospital system, a specialist or an entire medical group effective January 1, and that change is easy to miss for anyone who simply re-enrolls. Confirming that each doctor is still in network is a separate step from confirming the plan still exists.

The risk falls hardest on people tied to one physician or facility. That might be a cardiologist managing a heart condition, an oncologist overseeing an active course of treatment, or a primary care doctor holding decades of records. Losing in-network status for that provider leaves two choices. One is paying out-of-network rates, which many Medicare Advantage HMOs do not cover at all outside emergency and urgent care. The other is transferring care to someone new.

Plan directories are the standard place to check, and they are not always current. Calling the doctor's office directly tends to produce a more reliable answer. Ask which Medicare Advantage plans the practice will accept for the coming year, since the staff there know which contracts have been signed. Hospital systems often publish the same list for the plans they participate in. Frame the question around next year specifically — a contract running through December can lapse on the 31st.

Contract disputes between large health systems and insurers are a routine feature of this market, and some are still unresolved when open enrollment closes. A beneficiary looking at an open dispute in early December has to decide how much uncertainty to accept.

Original Medicare works differently on this point. Any provider nationwide who accepts Medicare assignment will take it, which removes network geography from the equation. That matters for people who travel, split the year between two states, or seek treatment at a distant specialty center. The trade-off is usually cost, since Original Medicare pairs with a separate Part D plan and, for many people, a supplemental policy carrying its own premium. Network stability and monthly cost can only be weighed against each other if the change is spotted before December 7, not discovered at a January appointment.

Illustration: Quartz

Beneficiaries with limited income and savings can get help paying Medicare premiums and prescription costs, and many who qualify never apply. Two programs do most of this work: Extra Help, formally the Low-Income Subsidy, which reduces Part D costs, and Medicare Savings Programs, run through state Medicaid agencies, which can pay the Part B premium.

Extra Help lowers or eliminates the Part D premium and deductible and caps what a person pays at the pharmacy counter. Medicare Savings Programs come in several forms. The most comprehensive of them, the Qualified Medicare Beneficiary program, also covers Medicare deductibles, coinsurance and copayments. Qualifying for a Medicare Savings Program enrolls someone in Extra Help automatically, so a single application can unlock both.

People skip these programs mainly because they assume they earn too much or hold too much in the bank. Eligibility limits track the federal poverty guidelines and are updated each year, and several states set more generous thresholds than the federal baseline or disregard assets entirely. Eligibility rests on current circumstances rather than career earnings, so someone whose income fell after leaving work may qualify now even if an earlier check came back negative.

Neither program is tied to the October 15 through December 7 window. Extra Help applications go to the Social Security Administration and can be filed at any point in the year, and Medicare Savings Program applications go to the state Medicaid office on the same open-ended basis. Fall is still a sensible time to check, since the household is already gathering income figures and comparing drug costs.

There is a scheduling benefit as well. People receiving Extra Help get additional opportunities during the year to change Part D or Medicare Advantage prescription drug plans, rather than being held to the single fall window everyone else works within.

A SHIP counselor can screen for eligibility and help complete the paperwork at no cost, and the Social Security Administration accepts Extra Help applications online. Checking deliberately beats waiting for a notice in the mail.

Illustration: Quartz

Leaving Original Medicare and a Medigap policy for a Medicare Advantage plan can be a one-way door. Medigap insurers are required to sell a policy regardless of health history only during limited windows. Outside those windows, most states let an insurer deny an applicant or charge more based on medical underwriting.

The main protection is the Medigap open enrollment period: six months that start the month a person is both 65 or older and enrolled in Part B. In that window an insurer cannot refuse to sell a policy or raise the premium because of health problems. It can impose a waiting period of up to six months before covering a pre-existing condition, and only when the applicant comes in without prior creditable coverage. Once the six months pass, the window does not reopen.

Federal law adds a short list of guaranteed-issue rights, including what are known as trial rights. A person who enrolled in Medicare Advantage when first eligible at 65 and returns to Original Medicare within 12 months can buy a Medigap policy without underwriting. The same right covers someone who dropped a Medigap policy for the first time to try Medicare Advantage and switches back within 12 months; that person can return to the old policy if the insurer still sells it. Other guaranteed-issue rights apply in narrow cases, such as a plan pulling out of the service area.

State rules change the calculation. New York and Connecticut require insurers to sell Medigap policies year-round on a guaranteed-issue basis, so residents there can move between coverage types without facing underwriting later. A state insurance department or a counselor at the State Health Insurance Assistance Program can confirm what applies locally.

Two further constraints matter. A Medigap policy cannot pay the cost sharing under a Medicare Advantage plan, so carrying both is not possible. And Plans C and F are closed to anyone who became eligible for Medicare on or after January 1, 2020, which narrows the choices for a returning beneficiary even when a guaranteed-issue right applies.

Check what the route back into Medigap looks like before giving it up.

Illustration: Quartz

Dental, vision and hearing coverage is the most heavily advertised feature of Medicare Advantage plans, and it is also the feature most likely to shrink quietly from one year to the next. Original Medicare does not cover routine dental care, eye exams for glasses, or hearing aids, which is why these extras carry so much weight in plan marketing.

What a plan actually pays for varies widely. One plan may cover cleanings and X $TWTR-rays but exclude crowns, root canals and dentures. Another may include major services while capping the annual allowance at a figure a single crown would use up. Hearing benefits often take the form of a fixed allowance toward devices bought through a contracted supplier, not coverage for any hearing aid a person chooses. Vision benefits may pay for one routine exam a year plus a limited frame allowance, with contact lenses treated separately.

Any of those terms can be revised at renewal while the plan's advertising still lists dental, vision and hearing as included. A smaller allowance, a narrower dentist network or a new limit on how often a device can be replaced does not change the headline.

The document that spells out the details is the Evidence of Coverage, which runs far longer than any brochure. Summary materials and television commercials confirm that a benefit exists. They rarely state its dollar limit, its waiting periods, or whether a specific dentist or audiologist participates.

Call the provider's office directly and ask which Medicare Advantage plans it takes. Supplemental benefit networks are often separate from a plan's medical network and run by a third-party vendor, so a dentist listed in one may be absent from the other.

The stakes rise for anyone with work already scheduled — implants, a bridge, new hearing aids or replacement glasses. A person who picked a plan for its dental allowance and budgeted a procedure around that number can owe far more if the allowance drops. The bill often arrives before the change is noticed.

Illustration: Quartz

A health change since the last enrollment season should trigger a fresh plan comparison, not an autopilot renewal. A plan built around two generic prescriptions and one annual physical rarely still fits six months after a diagnosis of heart failure, rheumatoid arthritis or cancer.

New conditions add cost in three places at once: medications, specialist visits and procedures. Plans price each of those differently, and the differences grow as use goes up. A flat copay per specialist visit looks cheap to someone seeing a doctor twice a year. That same copay applied to weekly or monthly appointments produces a very different annual total.

Coinsurance behaves the same way. It charges a percentage of a service's cost rather than a set dollar amount, so it stays small on a routine office visit. Applied to an infusion drug or a series of scans, it can become one of the largest line items of the year.

Where a drug is administered matters as well. Medications given in a doctor's office or an infusion center are generally billed under Part B rather than Part D. That means a different cost-sharing structure than the one listed on a prescription formulary.

Prior authorization rules carry more weight after a diagnosis. Many Medicare Advantage plans require approval before covering infusions, advanced imaging or a skilled nursing stay, and HMO plans typically require a referral before a specialist visit is covered. Someone beginning treatment will run into those requirements repeatedly.

A diagnosis also attaches a person to specific clinicians — an oncologist, a cardiologist, a particular treatment center. Whether those providers are contracted for the coming year becomes a deciding factor rather than a footnote.

Family members and caregivers helping with enrollment should ask directly whether anything has changed medically since last fall. Someone in the early weeks of treatment is focused on appointments and side effects, not insurance paperwork, and the question is easy to skip. Asking it turns a routine renewal into an accurate one.