Medicare mistakes can become expensive when they involve enrollment deadlines, prescription drug coverage, supplemental insurance, or assumptions about services Medicare pays for. Some errors may result in higher monthly premiums for years, while others can leave you responsible for significant medical or long-term care expenses.
The challenge is that Medicare has several parts, enrollment periods, private-plan options, and cost-sharing rules. The coverage that works well for one person may be a poor match for another person's doctors, prescriptions, budget, or travel needs.
Understanding the most common problems can help you compare coverage more carefully and recognize which questions deserve attention before you enroll or switch plans.
1. Medicare Mistakes Often Begin With Missing Enrollment Deadlines
One of the first areas to understand is Medicare enrollment.
Most people first become eligible for Medicare around age 65, although eligibility rules differ for certain people who qualify earlier because of a disability or specific medical conditions.
Delaying Part B without qualifying for an applicable Special Enrollment Period can become costly. In 2026, the standard Part B premium is $202.90 per month. The Part B late-enrollment penalty generally adds 10% for each full 12-month period that a person could have enrolled in Part B but did not. In most cases, that additional amount continues for as long as the person has Part B.
That means a delay of two full years could result in a 20% penalty added to the standard Part B premium. The actual dollar amount can change because Medicare premiums are updated over time.
However, turning 65 does not automatically mean everyone needs to make exactly the same enrollment decision. People who remain covered through qualifying current employment may have different enrollment options.
What to check: Before delaying Part B, verify whether your existing insurance allows you to qualify for a Special Enrollment Period later. Do not assume that every employer, retiree, COBRA, or other health plan creates the same Medicare enrollment rights.
2. Going Too Long Without Creditable Drug Coverage May Cost More
Prescription drug coverage has its own enrollment rules.
A Medicare late enrollment penalty can apply to Part D when an eligible person goes 63 consecutive days or longer without Medicare drug coverage or other creditable prescription drug coverage.
Creditable coverage is drug coverage expected to pay, on average, at least as much as Medicare's standard drug coverage. Coverage through an employer, union, TRICARE, the Department of Veterans Affairs, or certain other sources may qualify.
For 2026, Medicare uses a national base beneficiary premium of $38.99 to calculate the Part D penalty. The penalty generally equals 1% of that amount multiplied by the number of full uncovered months. The result is rounded to the nearest $0.10 and added to the monthly premium.
Because the national base beneficiary premium may change each year, the dollar amount of an existing penalty may change as well.
Keeping documentation showing that previous prescription coverage was creditable can be useful if Medicare later requests proof.
3. Assuming Medicare Covers Every Health Expense
Some of the most expensive Medicare coverage gaps have little to do with enrollment deadlines.
Original Medicare does not cover every medical or personal-care expense. Examples of services generally excluded include:
- Long-term custodial care
- Most routine dental care
- Eye exams for prescription eyeglasses
- Hearing aids and fitting exams
- Routine physical exams
- Certain other non-covered services
Long-term care deserves particular attention. Medicare does not pay for long-term custodial care, such as ongoing assistance with bathing, dressing, eating, or other everyday activities when that is the type of care a person needs.
That differs from qualifying skilled nursing facility care, which Medicare Part A may cover when applicable requirements are satisfied.
People planning retirement may therefore need to consider how they would pay for services outside Medicare. Depending on their circumstances, possible resources can include personal savings, qualifying Medicaid coverage, private long-term care insurance, or other financial arrangements.
4. Choosing Between Original Medicare and Medicare Advantage Without Comparing Details
Choosing coverage based primarily on the monthly premium can overlook important differences.
Original Medicare generally lets beneficiaries receive covered care from any doctor or hospital in the United States that accepts Medicare. People can add separate Part D prescription coverage and may choose to purchase Medigap coverage.
Medicare Advantage plans, by comparison, are Medicare-approved private health plans that provide Part A and Part B benefits and usually include Part D coverage. Many offer additional benefits, such as certain dental, hearing, or vision services.
However, provider access may differ.
An HMO generally requires members to use providers within its network for covered non-emergency services, subject to specified exceptions. A PPO generally provides more flexibility to use out-of-network providers, although doing so will usually cost more.
What Should You Compare Before Choosing a Plan?
Consider checking:
- Monthly premiums
- Deductibles
- Copayments and coinsurance
- Annual out-of-pocket limits where applicable
- Prescription formularies
- Pharmacy networks
- Doctor and hospital networks
- Referral requirements
- Prior-authorization rules
- Extra benefits
- Coverage when traveling
A plan with a low premium may still result in higher overall costs if important medications fall into expensive formulary tiers or frequently used providers are outside the network.
The appropriate comparison is therefore based on expected total costs and access to care rather than the premium alone.
5. Missing the Best Time to Purchase Medigap
People who choose Original Medicare may consider Medicare Supplement Insurance, commonly called Medigap, to help cover certain out-of-pocket costs.
The Medigap Open Enrollment Period is especially important.
Under federal rules, this six-month period begins the first month you have Medicare Part B and are 65 or older. During this period, you can generally purchase any Medigap policy sold to you in your state, and insurers cannot deny coverage because of pre-existing health problems.
After this enrollment window closes, buying Medigap may become more difficult or expensive unless you have another guaranteed-issue right or applicable state protection.
Medigap should also be evaluated based on what it actually covers. Policies primarily help pay certain cost-sharing expenses associated with Original Medicare. They generally do not cover long-term care, routine dental or vision care, hearing aids, or private-duty nursing.
For standardized Medigap plans, comparing premiums among insurers offering the same lettered plan can be worthwhile because standardized plans of the same letter provide the same basic benefits, although pricing and company-related factors can differ.
6. Failing to Check Provider Networks Before Enrolling
A doctor accepting Medicare does not automatically mean that doctor participates in every private Medicare plan.
This distinction matters particularly with Medicare Advantage.
Someone considering a plan should verify the participation of:
- Primary care doctors
- Specialists
- Preferred hospitals
- Pharmacies
- Medical facilities
- Other regularly used providers
Checking the insurer's current provider directory is useful, but confirming important relationships directly with the plan and provider can add another layer of protection before enrollment.
Prescription drugs deserve the same scrutiny. Plans can have different formularies, pharmacy arrangements, utilization-management requirements, and cost-sharing structures.
7. Confusing Medicare's Different Annual Enrollment Periods
Medicare has multiple enrollment periods, and they do not provide identical options.
The annual Medicare Open Enrollment Period runs from October 15 through December 7. During this period, beneficiaries can make qualifying changes such as moving between Original Medicare and Medicare Advantage, switching Medicare Advantage plans, or changing drug coverage. Changes generally become effective January 1.
The Medicare Advantage Open Enrollment Period runs from January 1 through March 31 for people already enrolled in Medicare Advantage. During this period, an eligible member can generally make one change by switching to another Medicare Advantage plan or returning to Original Medicare, with an opportunity to join a separate drug plan when applicable.
Special Enrollment Periods may become available following qualifying life events or changes in coverage.
Understanding which period applies can prevent someone from assuming they can change coverage whenever they want.
8. Ignoring Income-Related Medicare Premium Adjustments
Higher-income beneficiaries can pay more for Part B and Part D.
The additional amount is commonly known as Medicare IRMAA, or the income-related monthly adjustment amount.
For 2026, the standard Part B premium is $202.90 per month. For most individual tax filers, IRMAA begins when the modified adjusted gross income used for the determination exceeds $109,000. For most married couples filing jointly, it begins above $218,000.
At the highest 2026 income tier, the total monthly Part B premium reaches $689.90. Part D can carry a separate income-related adjustment in addition to the premium charged by the chosen drug plan.
The Social Security Administration generally determines these adjustments using federal tax information supplied by the IRS.
A person who recently retired may therefore encounter a higher premium based on income from an earlier year when earnings were higher.
Can IRMAA Be Reduced After Retirement?
Potentially.
If your income decreases because of an eligible life-changing event, Social Security allows you to request a new determination using more recent information. Examples of qualifying events can include work stoppage, work reduction, marriage, divorce, or the death of a spouse.
Form SSA-44 is available for requesting a reduction when the applicable requirements are met.
9. Automatically Renewing a Medicare Advantage or Drug Plan
Keeping the same plan every year may be convenient, but convenience should not replace an annual review.
Private Medicare plan details can change from one year to another. Depending on the plan, changes might involve premiums, deductibles, copayments, provider networks, covered drugs, pharmacy arrangements, or supplemental benefits.
An annual review should compare the upcoming plan year with your current health needs.
Pay particular attention when:
- You started taking new medications.
- Your preferred physician or hospital changed.
- You expect surgery or specialist care.
- Your prescription costs increased.
- Your financial situation changed.
- You moved.
- Your current plan changed its benefits or network.
Someone whose plan worked well this year may find that another option better matches their needs next year—or that keeping the current plan remains appropriate after comparison.
10. Comparing Medicare Plans Based Only on Extra Benefits
Dental, vision, hearing, fitness, transportation, and other supplemental benefits can make certain Medicare Advantage options attractive.
However, those benefits should be considered alongside the plan's core medical coverage and costs.
A plan offering several extra benefits may have a provider network, prescription formulary, authorization requirements, or cost-sharing arrangement that does not match your health needs.
Before choosing a plan, ask how frequently you expect to use its major medical benefits compared with its supplemental features.
Extra benefits can have meaningful value, but the details and limitations of each benefit matter.
What Medicare Costs Should You Compare?
A useful comparison looks beyond the advertised monthly premium.
| Cost or Feature | Why It Matters |
|---|---|
| Monthly premium | Determines the recurring cost of maintaining coverage |
| Deductible | Shows how much you may pay before certain coverage begins |
| Copayments | Can add up with frequent appointments or prescriptions |
| Coinsurance | May create larger costs for expensive services |
| Drug formulary | Determines whether and how your medications are covered |
| Provider network | Affects access to doctors, hospitals, and other providers |
| Out-of-pocket maximum | Limits covered Part A and Part B spending in Medicare Advantage |
| Supplemental coverage | May help address specific services or Original Medicare cost sharing |
For Original Medicare, beneficiaries generally pay 20% of the Medicare-approved amount for most Part B services after meeting the Part B deductible. In 2026, that annual deductible is $283.
Medicare Advantage plans use different cost-sharing structures and have yearly limits on out-of-pocket spending for covered Part A and Part B services.
As a result, comparing potential annual costs under realistic health-care scenarios may provide more useful information than comparing premiums alone.
Frequently Asked Questions About Medicare Mistakes
What Is One of the Most Expensive Medicare Errors?
There is no single error that costs everyone the most because the financial impact depends on individual circumstances. Long-term enrollment penalties, uncovered long-term care, high cost sharing, and choosing coverage that poorly matches someone's providers or prescriptions can all create substantial expenses.
Does Medicare Cover Long-Term Nursing Home Care?
Medicare generally does not cover long-term custodial care. It may cover qualifying skilled nursing facility care for a limited period when Medicare's requirements are satisfied. Medicaid may cover certain long-term care for eligible individuals.
Is Medicare Advantage Always Cheaper Than Original Medicare?
No. Costs depend on the specific plan, medical services used, prescriptions, providers, supplemental coverage, and other factors. Medicare Advantage plans have annual out-of-pocket limits for covered Part A and Part B services, while Original Medicare does not have an annual out-of-pocket maximum unless supplemental coverage provides additional financial protection.
Should You Buy Medigap as Soon as You Turn 65?
Not necessarily. The relevant federal enrollment window generally begins when you are 65 or older and enrolled in Part B. Employment coverage and other circumstances can affect timing. Anyone delaying Part B should confirm how their existing coverage affects Medicare and future Medigap options.
Should You Review Medicare Coverage Every Year?
An annual review can be useful, especially for people enrolled in private Medicare Advantage or Part D plans. Plan costs, formularies, provider arrangements, and benefits may change, while your medical and prescription needs can change as well.
How to Reduce the Risk of Costly Medicare Mistakes
Medicare decisions become easier to manage when you separate them into three areas: timing, coverage, and total cost.
Start by confirming when you need to enroll and whether existing employer or other insurance qualifies you for an enrollment exception. Next, determine which services and prescriptions you expect to use and identify potential gaps. Finally, compare premiums with deductibles, copayments, coinsurance, drug costs, provider access, and other expenses.
For people considering private coverage, comparing multiple available plans can help reveal differences that a monthly premium alone does not show. Those choosing Original Medicare may want to evaluate Part D and Medigap options separately.
Medicare rules, premiums, plan availability, and benefits can change. Before enrolling, dropping coverage, or switching plans, verify current information through Medicare, Social Security, the insurer, and other relevant official sources.
Making a careful comparison may not eliminate every future health-care expense, but it can help you understand what you are buying, what Medicare may leave uncovered, and which costs need room in your retirement budget.
