Medicare Open Enrollment Mistakes That Cost Money

The Medicare Annual Enrollment Period runs from October 15 to December 7 each year, and it represents one of the most consequential windows on the senior healthcare calendar. During these weeks, millions of beneficiaries can switch Medicare Advantage plans, move between Original Medicare and Medicare Advantage, or add and drop Part D prescription drug coverage. The decisions made in this narrow timeframe lock in costs, networks, and drug coverage for the entire following calendar year. That is exactly why Medicare open enrollment mistakes that cost money can quietly drain hundreds or even thousands of dollars from a household budget, often without the beneficiary realizing anything went wrong until a claim is denied or a pharmacy bill spikes in January.

At NewMedicare.com, a privately operated educational resource and service platform, licensed agents regularly speak with beneficiaries who made rushed choices during AEP and later discovered gaps in coverage. The good news is that nearly every costly error is preventable with the right information and a bit of preparation. This guide walks through the most expensive open enrollment mistakes, explains why each one hurts, and shows how to sidestep them before the December 7 deadline arrives.

Why Medicare Open Enrollment Mistakes Are So Expensive

Unlike many consumer decisions, Medicare plan choices are sticky. Once the calendar flips to January 1, most beneficiaries are locked into their selections for a full year unless they qualify for a Special Enrollment Period. A plan that looked attractive in October because of a $0 premium might turn out to have a restrictive network, a hefty deductible, or a formulary that does not cover a critical medication. By the time the problem surfaces, the window to fix it has usually closed.

Costs compound in ways that are not always obvious. A drug that was covered at $40 per month under one plan could cost $400 per month under another. A hospital stay that would have been capped under Original Medicare plus a Medigap policy could generate thousands in coinsurance under a Medicare Advantage plan with a high out-of-pocket maximum. Even something as simple as failing to verify that a preferred doctor participates in a new plan's network can lead to paying full price for routine visits.

The stakes are high enough that beneficiaries should treat AEP like a financial planning event rather than a paperwork formality. Reviewing the Annual Notice of Change, comparing formularies, and confirming provider participation takes a few hours, but those hours routinely save four figures over the course of a year.

Mistake One: Ignoring the Annual Notice of Change

Every fall, Medicare Advantage and Part D plans mail or email an Annual Notice of Change document, often abbreviated as ANOC. This packet details exactly how the plan will change on January 1, including premium adjustments, deductible shifts, changes to the drug formulary, and updates to provider networks. Many beneficiaries toss it in the recycling bin assuming nothing important has changed. That assumption is frequently wrong.

Plans renegotiate contracts with pharmacies, hospitals, and physician groups every year. A specialist who was in-network in December may be out-of-network in January. A tier-one generic may be moved to tier three, tripling the copay. Premiums can rise by double-digit percentages. The ANOC is the single most reliable early warning system a beneficiary has, and reading it carefully is the first line of defense against costly surprises.

Beneficiaries who want a structured way to act on what they find in the ANOC can follow a simple review sequence:

1. Compare the new premium and deductible against the current year to quantify the change.
2. Check whether each prescription still appears on the formulary and at what tier.
3. Verify that primary care doctors, specialists, and preferred hospitals remain in-network.
4. Note any new prior authorization requirements or step therapy rules.
5. Decide whether to stay, switch, or explore a different plan type entirely.

Completing this review before mid-November leaves plenty of time to explore alternatives and enroll in a better-fitting plan. Waiting until the first week of December often forces a rushed decision, which is precisely how expensive mistakes happen.

Mistake Two: Choosing a Plan Based Only on Premium

A $0 premium Medicare Advantage plan is appealing, and for some beneficiaries it is genuinely the best option. The mistake is treating the premium as the only number that matters. Total annual cost includes premiums, deductibles, copays, coinsurance, and the out-of-pocket maximum. A plan with no monthly premium but a $7,500 out-of-pocket maximum can cost far more in a bad health year than a plan with a $40 monthly premium and a $3,400 maximum.

The same logic applies to Part D. A standalone drug plan with a low premium may have a high deductible and limited formulary coverage, while a slightly more expensive plan may cover the same medications at a much lower tier. Beneficiaries who take several brand-name drugs often find that the plan with the higher premium is actually the cheaper choice once pharmacy costs are factored in.

A useful framework is to estimate total annual spending under each plan using three scenarios: a healthy year with minimal care, an average year with routine visits and a few prescriptions, and a high-cost year involving a hospital stay or a new specialty drug. Comparing plans across all three scenarios prevents the trap of optimizing for the best case while ignoring the worst. For a deeper look at timing and deadlines, the guide on the Medicare Open Enrollment 2026 deadline explains how the calendar interacts with plan selection.

Mistake Three: Failing to Check the Drug Formulary

Formularies, the lists of covered prescription drugs, change every year. A medication that was covered at a low copay in 2025 may be dropped, moved to a higher tier, or subjected to prior authorization in 2026. Beneficiaries who do not check the formulary before enrolling can discover in January that a maintenance drug now costs hundreds of dollars per month out of pocket.

This mistake is especially painful because it is entirely avoidable. Every plan publishes its formulary online, and Medicare's Plan Finder tool allows users to enter their medication list and see estimated costs across plans. NewMedicare.com also connects beneficiaries with licensed agents who can run these comparisons quickly and flag any drugs that are not covered or that require extra paperwork.

Beneficiaries should also confirm that their preferred pharmacy is in the plan's network. Some plans differentiate between preferred pharmacies and standard pharmacies, and using the wrong one can double a copay. Mail-order options sometimes reduce costs further, but only if the plan supports them for the specific medication.

Mistake Four: Overlooking Provider and Hospital Networks

Medicare Advantage plans operate within networks, and those networks vary widely from plan to plan and year to year. A beneficiary who enrolls in a plan without verifying that their cardiologist, oncologist, or preferred hospital participates may face full out-of-network costs or be forced to change doctors mid-treatment. For someone managing a chronic condition, that disruption can be both financially and medically damaging.

Original Medicare, by contrast, generally allows beneficiaries to see any provider who accepts Medicare nationwide, which is why many people pair it with a Medigap policy for predictable costs. Beneficiaries who value flexibility often find that Medigap Plan G or Plan N offers a better long-term fit than a narrow-network Advantage plan, even if the monthly premium is higher.

Before enrolling in any Medicare Advantage plan, beneficiaries should call their doctors' offices directly and ask whether the specific plan will be accepted in the coming year. Network directories on insurance websites are sometimes outdated, so a phone call provides certainty that a PDF cannot.

Mistake Five: Missing the Deadline or Enrolling Late

The Annual Enrollment Period ends on December 7. Applications submitted after that date are generally not accepted unless the beneficiary qualifies for a Special Enrollment Period. Missing the deadline means staying in the current plan for another year, even if that plan has become a poor fit. In some cases, beneficiaries who miss their Initial Enrollment Period around age 65 face permanent late enrollment penalties on Part B and Part D.

Late enrollment penalties are among the most expensive long-term mistakes in Medicare. The Part B penalty adds 10 percent to the premium for every 12-month period of delayed enrollment, and that surcharge lasts for as long as the beneficiary has Part B. The Part D penalty is calculated similarly and also persists for life. These penalties are avoidable with timely action, which is why calendar reminders in September and October are so valuable.

Beneficiaries who are unsure whether they qualify for a Special Enrollment Period, or who need help understanding how a move, job loss, or disability status affects their options, can benefit from professional guidance. NewMedicare.com offers complimentary, no-commitment assistance from licensed agents who can clarify eligibility and walk through the enrollment process step by step.

Mistake Six: Assuming Doctors and Drugs Stay Covered

Continuity of care is one of the most underappreciated factors in Medicare planning. Even beneficiaries who are happy with their current plan should verify each year that nothing has changed. A plan that covered a specific specialist in 2025 may have renegotiated that contract for 2026. A drug that was on tier two may now be on tier four. These changes rarely make headlines, but they show up on pharmacy receipts and explanation of benefits statements.

Verification takes only a few minutes per provider and per medication, and it prevents the unpleasant scenario of discovering a coverage gap after a service has already been received. Beneficiaries who take multiple medications or see several specialists should build this check into their annual fall routine alongside reading the ANOC.

Mistake Seven: Skipping Help That Is Free

Many beneficiaries try to navigate open enrollment alone, assuming that professional help comes with a fee or a sales pitch. In reality, licensed insurance agents who work with platforms like NewMedicare.com provide their services at no cost to the beneficiary. Agents are compensated by insurance carriers, not by the people they help, and they can compare plans from multiple carriers side by side.

Working with an agent does not obligate a beneficiary to enroll in anything. It simply adds a knowledgeable second set of eyes to a process that is genuinely complex. Agents can flag formulary issues, confirm network participation, estimate total annual costs, and ensure that enrollment paperwork is submitted correctly and on time.

For beneficiaries who prefer to research independently, NewMedicare.com also provides educational resources covering Medicare Parts A, B, C, and D, Medigap, and enrollment periods. The combination of self-service tools and live agent support gives beneficiaries flexibility in how they approach the decision. Those who want to explore broader coverage options beyond Medicare, including ACA Marketplace and short-term plans, can also review resources at NewHealthInsurance.com for additional context.

How to Avoid These Mistakes: A Practical Checklist

Avoiding costly open enrollment errors comes down to preparation and verification. The beneficiaries who save the most money are typically the ones who start reviewing their options in early October rather than the final week of November. They read the ANOC, compare total costs rather than premiums alone, check formularies and networks, and confirm deadlines.

Here is a concise checklist that captures the highest-value actions:

• Read the Annual Notice of Change from cover to cover and note every cost or coverage shift.
• List all prescriptions, dosages, and preferred pharmacies before comparing plans.
• Confirm that every doctor and hospital you use will be in-network next year.
• Compare plans using total estimated annual cost, not just the monthly premium.
• Mark December 7 on the calendar and submit any enrollment changes at least a week early.

Following this checklist takes a few hours, but it routinely prevents four-figure mistakes. Beneficiaries who want personalized help can request a complimentary quote from NewMedicare.com and speak with a licensed agent who can run through the same steps in a single phone call.

Final Thoughts on Protecting Your Medicare Budget

Medicare open enrollment mistakes that cost money almost always trace back to incomplete information or last-minute decisions. The system rewards beneficiaries who plan ahead, read their plan documents, and ask questions before the deadline rather than after. Premiums, formularies, networks, and out-of-pocket maximums all shift annually, and the only way to stay ahead of those changes is to review them deliberately each fall.

NewMedicare.com exists to make that review easier. The platform provides unbiased educational content, side-by-side plan comparisons, and access to licensed agents who can answer questions without pressure or obligation. Beneficiaries who take advantage of these resources before December 7 put themselves in the best possible position to keep their healthcare costs predictable and their coverage aligned with their actual needs.