When Is Medicare Open Enrollment?
When Is Medicare Open Enrollment?
When is Medicare open enrollment? The primary annual window — the Annual Enrollment Period, or AEP — runs from October 15 to December 7 every year. Changes made during Medicare open enrollment take effect on January 1 of the following year. Even if your current plan has served you well, reviewing it annually during Medicare open enrollment is not optional housekeeping — it is the most important recurring financial decision most retirees make each year. Medicare plans change every year. Formularies change, networks change, premiums and copays change, and the plan that was the right choice last year may be significantly less optimal this year based on changes to your medications, your providers, or the plan’s own cost structure. Medicare open enrollment exists precisely because these changes are predictable and annual — and ignoring the window means accepting whatever your current plan has become rather than choosing what best fits your current situation.
At Diversified Insurance Brokers, we help beneficiaries navigate Medicare open enrollment with a structured comparison process focused on three things: keeping your doctors, covering your medications at reasonable cost, and aligning premium and out-of-pocket structure with your retirement budget. This page explains every Medicare enrollment window, what you can and cannot change during each one, what the most common and costly open enrollment mistakes look like, and how to prepare for a comparison that is based on your actual providers and prescriptions rather than generic plan rankings. If you are approaching open enrollment and want help comparing plans, the tools and request forms below connect you with our licensed Medicare team.
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Every Medicare Enrollment Window Explained
Medicare has multiple enrollment windows, and confusing them is one of the most common and costly mistakes retirees make. Understanding which window applies to which situation — and what can and cannot be changed during each one — prevents both missed opportunities and incorrect assumptions about what is possible when.
Annual Enrollment Period (AEP): October 15 – December 7. This is the primary Medicare open enrollment window, the one most people are thinking of when they ask “when is Medicare open enrollment?” During AEP, you can switch from Original Medicare to Medicare Advantage, switch from Medicare Advantage back to Original Medicare, switch between Medicare Advantage plans, change your Part D prescription drug plan, or drop Part D if you have other creditable prescription coverage. Changes made during AEP take effect January 1. You do not have to make a change — if you are satisfied with your current plan after reviewing it, you can stay. But reviewing it is essential because plan terms change every year even when you do nothing.
Medicare Advantage Open Enrollment Period (MA OEP): January 1 – March 31. This window is specifically for people already enrolled in a Medicare Advantage plan on January 1. During the MA OEP, you can switch from your current Advantage plan to a different Advantage plan, or return to Original Medicare and add Part D. You cannot use the MA OEP to switch from Original Medicare to a Medicare Advantage plan. This window exists as a correction mechanism — if a plan choice made during AEP turns out to be wrong once the plan year begins (a provider left the network, a drug formulary is worse than anticipated), the MA OEP provides a limited window to fix it. Changes made during MA OEP take effect the first day of the following month.
Initial Enrollment Period (IEP). For people first becoming Medicare-eligible, the Initial Enrollment Period is a seven-month window — three months before the month you turn 65, the month of your birthday, and three months after. This is when most people first sign up for Medicare Parts A and B. Delaying enrollment outside the IEP without qualifying coverage (such as employer group health insurance from current employment) can trigger permanent late enrollment penalties for Part B and Part D that remain in effect for the life of the coverage. Understanding how to enroll in Medicare at 65 during the IEP and avoiding the timing mistakes described in our guide to Medicare enrollment mistakes to avoid is critically important for anyone approaching initial eligibility.
Special Enrollment Periods (SEPs). Special enrollment periods allow changes outside of the standard annual windows when specific qualifying life events occur. Common qualifying events include losing employer-sponsored coverage, moving out of a plan’s service area, gaining or losing Medicaid eligibility, and certain plan terminations or changes. If you are working past 65 with employer group coverage, understanding how your employer coverage interacts with Medicare enrollment — specifically when you can delay Medicare without penalty and when you must enroll to avoid penalties — requires careful analysis. Our guide to how to get Medicare while working covers this in detail.
What You Can Change During Medicare Open Enrollment (AEP)
The Annual Enrollment Period provides the broadest range of plan change options of any regular Medicare enrollment window. Understanding exactly what is available helps you approach the comparison with the right scope — evaluating all relevant options rather than assuming a change is not possible when it is.
If you are currently on Original Medicare (Parts A and B), you can use AEP to enroll in a Medicare Advantage plan for the first time, add a Part D prescription drug plan if you do not have one, change your existing Part D plan, or review whether a Medicare Supplement (Medigap) plan might reduce your cost-sharing exposure. Note that Medigap enrollment outside of your Medigap Open Enrollment Period (the six months starting when you are first enrolled in Part B at 65 or older) typically involves medical underwriting in most states — meaning health conditions may affect your ability to switch Medigap plans or your pricing if you do. AEP does not create a guaranteed-issue right to Medigap outside of the original open enrollment window in most states.
If you are currently on a Medicare Advantage plan, you can use AEP to switch to a different Medicare Advantage plan, return to Original Medicare (with or without adding Part D), or add, change, or drop a Part D plan if your Advantage plan includes prescription coverage through a separate Part D component. Switching between Advantage plans is one of the most common AEP actions — when a network or formulary change makes the current plan less suitable, moving to a plan with a more appropriate structure for the coming year is the appropriate response.
For a clear breakdown of the structural differences between Medicare Advantage and Medicare Supplement coverage before you compare, our Medicare Advantage vs. Medicare Supplement comparison provides a useful framework. Understanding the fundamental differences in how these two plan types work is essential context for evaluating which direction makes sense for your specific health profile, provider relationships, and financial priorities. For Part D specifically, our guide to Medicare Part D explained covers formulary mechanics, pharmacy tiers, and the coverage gap in plain language.
Why Annual Review Matters Even When You’re Satisfied With Your Plan
The most costly Medicare mistake most beneficiaries make is not a wrong decision — it is a non-decision. Auto-renewing without reviewing means accepting changes to your plan that you may not know have occurred and may not have accepted if you had been aware of them. Medicare plans change annually in ways that are disclosed in the Annual Notice of Change (ANOC) document that carriers are required to send before October 15. The Medicare Annual Notice of Change tells you specifically what is changing in your plan for the coming year — premium changes, copay adjustments, network changes, formulary tier changes for your specific medications, and benefit structure modifications. Reading this document carefully before open enrollment is the minimum responsible step for any Medicare beneficiary.
The specific changes that most commonly surprise beneficiaries are formulary changes — a medication that was covered at tier 2 may move to tier 3 or require prior authorization, instantly increasing its annual cost by hundreds or thousands of dollars depending on the medication. Network changes affect Medicare Advantage enrollees most directly: a hospital or specialist that was in-network last year may not be this year, which can create unexpected out-of-network expenses if the change is not caught before it affects access to care. Premium and copay changes are straightforward to identify — they are listed in the ANOC — but they must be evaluated in the context of what competing plans are offering for the coming year, not just compared to last year’s cost for the current plan.
How to Prepare for a Productive Medicare Open Enrollment Review
The most effective Medicare open enrollment reviews are personalized — built around your specific providers, prescriptions, pharmacy, and usage patterns rather than generic plan rankings. Generic rankings tell you which plans are “best” on average; a personalized review tells you which plan is best for you. These two answers are often different, which is why doing the work to gather the relevant information before comparing produces significantly better outcomes than relying on general guidance.
Before your review, gather: a complete and current list of your prescriptions (drug name, dosage, and frequency), your preferred pharmacy (and any secondary pharmacies you use when traveling), the names of the doctors and specialists you see regularly along with the hospital or system they are affiliated with, any planned procedures or therapies for the coming year, and your current plan’s ANOC if you have received it. These inputs allow a meaningful side-by-side comparison that answers the questions that actually matter — will my doctor be in-network? Will my prescriptions be covered at a cost I can afford? What is my realistic out-of-pocket exposure under each plan given my expected healthcare use?
Budget considerations are equally important context. Some beneficiaries strongly prefer a lower monthly premium even if it means higher copays when they use care — this works well when annual healthcare utilization is modest and predictable. Others prefer paying a higher premium in exchange for more predictable cost-sharing when they use care frequently — this works better for beneficiaries with ongoing specialist relationships, regular diagnostic testing, or prescription regimens that involve frequent pharmacy transactions. Neither preference is objectively correct; both are legitimate trade-offs that inform plan selection when the comparison is done with clear cost projections rather than premium comparison alone.
Understanding Medicare Advantage vs. Original Medicare for Open Enrollment Decisions
The most fundamental open enrollment decision for many beneficiaries is whether Medicare Advantage or Original Medicare plus a Medigap supplement better fits their situation. This is not a decision that can be made once and left indefinitely — it should be revisited periodically as health needs, provider relationships, and plan availability change over the course of retirement. AEP is the appropriate time to make this evaluation annually.
Medicare Advantage plans offer several structural advantages that appeal to many beneficiaries: lower monthly premiums (often $0 for MAPD plans that bundle Part D coverage), an annual out-of-pocket maximum that Original Medicare lacks, and often additional benefits like routine dental, vision, and hearing coverage that Original Medicare does not provide. The structural trade-offs are equally important: Advantage plans use provider networks, which means access to specific doctors and hospitals depends on the plan’s network and may change from year to year; cost-sharing through copays and coinsurance can accumulate significantly in high-utilization years, particularly for hospital stays and specialist visits; and many Advantage plans use prior authorization requirements for certain services and specialist referrals that can add administrative burden to managing care. For a comprehensive explanation of how Medicare Advantage works, see Medicare Part C explained.
Original Medicare plus a Medigap supplement provides a fundamentally different value proposition: broad provider freedom (any provider who accepts Medicare nationwide), no network restrictions or referral requirements, and more predictable cost-sharing because the Medigap plan absorbs much of what Original Medicare leaves uncovered. The trade-off is a higher monthly premium that covers both Part B and the Medigap supplement, plus a separate Part D plan for prescription coverage. For beneficiaries who travel frequently, who have multiple specialists they want to access without network restrictions, or who value maximum provider freedom over lower premiums, Original Medicare plus Medigap is often the more appropriate structure. The most common comparison our clients evaluate is Medicare Supplement Plan G versus Plan N, which breaks down the premium-versus-copay trade-off between the two most popular Medigap options.
The Retirement Income Connection: Budgeting Medicare Costs in Retirement
Medicare costs — premiums, copays, deductibles, and prescription expenses — are among the most significant and most variable ongoing expenses in retirement. The right Medicare plan for your financial situation is not just the one that minimizes premium; it is the one that produces the most predictable and manageable total healthcare cost relative to your retirement income structure. Beneficiaries who have guaranteed income covering their essential expenses can often absorb higher potential out-of-pocket variability from Medicare Advantage copays more comfortably than those whose retirement income is primarily drawn from investment accounts that are sensitive to market conditions.
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For retirees whose healthcare cost planning is tightly integrated with their retirement income strategy, the interaction between Medicare choices, IRMAA income thresholds (income-related Medicare premium adjustments), and the after-tax income available for healthcare spending is worth understanding in detail. Income that exceeds IRMAA thresholds increases Part B and Part D premiums, sometimes substantially, which means retirement income planning and Medicare cost planning are not independent questions. For retirees who are near IRMAA thresholds, coordinating Medicare enrollment decisions with broader retirement income planning — including Roth conversion timing, Social Security claiming strategy, and investment withdrawal sequencing — can produce meaningful savings in total healthcare premium costs over a multi-year retirement horizon.
Common Medicare Open Enrollment Mistakes and How to Avoid Them
The mistakes that produce the worst outcomes in Medicare open enrollment share a common characteristic: they are all avoidable with a modest amount of attention applied at the right time. Understanding what these mistakes look like makes them easy to avoid.
Auto-renewing without reviewing the ANOC. The Annual Notice of Change document that your carrier sends before October 15 tells you specifically what is changing in your plan. Not reading it means accepting changes you may not have chosen, and potentially missing a formulary or network change that materially affects your costs or access to care. Reading the ANOC takes 15 minutes and prevents year-long surprises that often can only be corrected at the next open enrollment.
Choosing based on premium alone. Premium is visible and easy to compare, so it naturally dominates plan comparison for many beneficiaries. But premium is rarely the most important cost factor for high-healthcare users. A plan with a $0 premium and high specialist copays can easily cost more in a year of normal healthcare use than a plan with a $100/month premium and low cost-sharing. Total expected annual cost — premium plus realistically projected copays, drug costs, and potential out-of-pocket exposure — is the correct comparison metric, not premium in isolation.
Not running prescriptions through the specific plan’s formulary. Formularies are plan-specific and they change annually. The plan that covered your most important medications at favorable tiers last year may not do so this year. Running your specific medication list through the Medicare Plan Finder or through our team’s comparison process before selecting a plan is the only way to know whether your medications will be covered at the tier and cost you expect. Generic rules — “Medicare Advantage plans cover more medications” or “Part D plans all cover the same drugs” — are simply not accurate.
Not confirming that specific providers are in-network for Advantage plans. Medicare Advantage networks change annually. A doctor who was in-network last year may not be this year. Before selecting or staying on a Medicare Advantage plan, confirming that your primary care physician, relevant specialists, and preferred hospital are in the plan’s network for the coming year is essential. This confirmation should come from the plan’s provider directory as of the upcoming plan year, not from the provider’s office staff, who may have outdated network information.
Missing the December 7 deadline. Open enrollment ends December 7. Changes submitted after that date generally cannot take effect January 1 and instead must wait for the next enrollment opportunity — which for many changes is the following October 15. Waiting until the last week of open enrollment creates time pressure that makes it harder to verify network and formulary details, harder to reach your advisor if you have questions, and harder to submit any necessary paperwork before the deadline. Starting your open enrollment review in October, as soon as the ANOC arrives and new plan information is published, gives you the full window to make a considered decision.
How Our Medicare Team Supports Open Enrollment
At Diversified Insurance Brokers, our licensed Medicare advisors provide personalized open enrollment support that goes beyond what any online comparison tool can offer. We take your specific medication list and run it through formularies. We verify that your providers are in the network for any Advantage plan we recommend. We model total expected annual cost — not just premium — across the plan options available in your area. And we explain the trade-offs in plain language so you can make the decision with confidence rather than uncertainty.
We are independent, which means we compare options from multiple carriers without any obligation to recommend a specific plan or carrier. Our advisors are licensed specifically in Medicare, which means they understand the product details, the enrollment rules, and the timing requirements at a level of specificity that general insurance agents often do not. If your open enrollment situation involves complexity — late enrollment questions, coordination with employer coverage, IRMAA issues, or Medigap underwriting concerns — we have the expertise to address those issues rather than simply pointing you to a plan comparison tool.
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FAQs: Medicare Open Enrollment
Medicare’s Annual Enrollment Period (AEP) — the primary open enrollment window — runs from October 15 to December 7 every year. Changes made during this period take effect January 1 of the following year. This window applies to current Medicare beneficiaries who want to review or change their coverage, and it is the only time of year when most beneficiaries can make major Medicare plan changes outside of qualifying special events. There is also a separate Medicare Advantage Open Enrollment Period that runs January 1 through March 31, but that window is limited to people already enrolled in a Medicare Advantage plan on January 1 — it does not allow switching from Original Medicare to a Medicare Advantage plan, and it has a more limited scope than AEP.
People who are first becoming Medicare-eligible have a separate Initial Enrollment Period that runs for seven months centered around their 65th birthday. This is a different window from the annual AEP and applies to first-time enrollment rather than plan changes. The timing of IEP enrollment matters significantly because late enrollment without creditable coverage triggers permanent premium penalties for Part B and Part D. For anyone approaching Medicare eligibility for the first time, understanding the IEP timeline and the consequences of missing it is as important as understanding the annual AEP for ongoing plan review.
Yes — during AEP (October 15 through December 7), you can switch from a Medicare Advantage plan back to Original Medicare. When you return to Original Medicare, you can also add a Part D prescription drug plan to cover prescriptions, or you can choose to add a Medicare Supplement (Medigap) plan to help cover the cost-sharing that Original Medicare leaves behind. Changes take effect January 1. If you decide you want to return to Original Medicare after January 1 of the new year, the Medicare Advantage Open Enrollment Period (January 1 through March 31) allows you to switch from Medicare Advantage to Original Medicare during that window as well, with changes taking effect the first day of the following month.
The Medigap dimension of returning to Original Medicare requires careful timing. When you are first enrolling in Part B (at age 65 or when you first get Medicare), you have a Medigap Open Enrollment Period during which carriers must accept you at standard rates regardless of health status. Outside of that initial window, Medigap carriers in most states can apply medical underwriting — meaning health conditions developed after your original Medicare enrollment may affect your ability to obtain Medigap coverage or the premium you pay for it. If you are returning to Original Medicare from a Medicare Advantage plan and want to add Medigap, checking whether guaranteed-issue rights apply to your specific situation before making the switch is essential to avoiding an unpleasant surprise.
No — if you take no action during Medicare open enrollment, your current plan automatically renews for the coming year. However, automatic renewal means accepting whatever changes your plan has made for the new plan year, which is why reviewing the Annual Notice of Change (ANOC) your carrier sends before October 15 is so important even if you intend to stay on the same plan. Formulary changes, network changes, premium increases, and copay adjustments all become effective on January 1 regardless of whether you were aware of them — automatic renewal is not a guarantee that the plan remains the same, it is simply a default continuation of enrollment in whatever the plan has become.
The practical implication is that “doing nothing” is itself a choice — it is choosing to accept the plan as it has been modified for the coming year without comparison to alternatives. For beneficiaries whose medications, health needs, or provider relationships have been stable, this may be a reasonable choice after confirming the plan’s changes are acceptable. For beneficiaries whose medications have changed, who have added new specialists, or whose plan has made material changes to formulary or cost-sharing, auto-renewal without review can be significantly more expensive than selecting a plan that better fits the current situation. Our Medicare team’s open enrollment review is designed to make this determination efficiently and clearly.
Yes — changing your Part D plan during AEP is one of the most common and most impactful open enrollment actions. Part D formularies change every year: medications can move between tiers, new prior authorization requirements can be added, preferred pharmacy networks can change, and new lower-cost generic options may become available on the formulary. The cumulative effect of these annual changes can be significant — a medication that cost $30 per month under your current plan may cost $150 per month under the same plan next year if it moves to a higher formulary tier, while a different plan may cover it at a $25 tier for the same period.
Running your specific medications through the Medicare Plan Finder or through a personalized comparison process using your actual drug list, dosages, and preferred pharmacy is the only reliable way to determine which Part D plan offers the best total prescription cost for your specific medication regimen. Generic guidance about which plans have the lowest premiums or which formularies are generally comprehensive does not produce the same accuracy as a medication-specific comparison, because formulary tiers and preferred pharmacy pricing are highly specific to each drug and each plan. This is one of the areas where working with a Medicare specialist who can run a personalized drug comparison produces meaningfully better outcomes than relying on general plan ratings.
Changes made during the Annual Enrollment Period (October 15 through December 7) take effect January 1 of the following year. This applies to all AEP changes regardless of when during the window you make them — whether you submit your plan change on October 16 or December 6, the coverage effective date is January 1. This is one reason why waiting until the final days of open enrollment creates unnecessary pressure: if there are any administrative issues, documentation questions, or plan verification needs, completing enrollment in the last few days leaves little time to resolve them before coverage needs to be in place.
Changes made during the Medicare Advantage Open Enrollment Period (January 1 through March 31) take effect the first day of the month following the enrollment request. So a change made on January 15 takes effect February 1, while a change made on March 1 takes effect April 1. Special Enrollment Period changes triggered by qualifying life events generally take effect on the first day of the month following the event or the enrollment request, depending on the specific qualifying event and the coverage type being changed. For anyone making a coverage change outside of AEP, confirming the effective date with the plan or with our Medicare team before discontinuing current coverage ensures there is no gap in protection during the transition.
Diversified Insurance Brokers provides personalized Medicare plan reviews through our licensed Medicare advisor team. Our comparison process is built around your specific situation — your prescriptions, your preferred providers, your pharmacy, your geographic area, and your retirement budget preferences — rather than generic plan rankings that may or may not be relevant to your particular circumstances. We compare options from multiple carriers independently, without obligation to recommend any specific carrier or plan. The comparison tool on this page allows you to start the initial review of what is available in your area, and requesting a review connects you with our licensed team for the personalized analysis that confirms the details matter most.
For beneficiaries who prefer government resources, Medicare.gov’s Plan Finder tool allows you to search plans in your zip code and filter by your medications and preferred pharmacy. State Health Insurance Assistance Programs (SHIPs) also provide free, unbiased Medicare counseling in every state through trained volunteer counselors. Our advisors provide a similar unbiased comparison service with the additional depth of insurance expertise and familiarity with the carrier and plan-specific details that SHIP counselors may not always have. Whatever resource you use, the critical input is your actual medication list, your actual providers, and a realistic assessment of how much healthcare you expect to use in the coming year — those specific inputs produce specific answers that generic plan comparisons cannot.
About the Author:
Tonia Pettitt, CMIP©, is a seasoned Medicare specialist with more than 40 years of hands-on experience guiding individuals and families through the complexities of Medicare planning. As a senior advisor with the nationally licensed independent agency Diversified Insurance Brokers, Tonia provides clear, dependable guidance across all areas of Medicare—including Medicare Advantage, Medicare Supplement (Medigap), and Part D prescription coverage. Leveraging active contracts with dozens of highly rated insurance carriers, she helps clients compare options objectively and secure the most suitable coverage for their health and budget.
Known for her patient, education-first approach, Tonia has built a reputation as a trusted resource for retirees seeking reliable, unbiased Medicare support. With four decades of experience across evolving Medicare laws, carrier changes, and plan structures, she brings unmatched insight to every client conversation—ensuring clients feel confident, protected, and fully prepared for each stage of their retirement healthcare journey.
Learn More About Medicare: Browse our complete guide to Medicare Insurance — covering Medicare Advantage, Supplement plans, Part A, B, C, D and enrollment strategies.
