Medicare Open Enrollment Ends Dec. 7—Should You Switch to Medigap?

Every fall, Medicare's Annual Enrollment Period generates a wave of TV commercials, mailers, and phone calls urging beneficiaries to review their coverage before the December 7 deadline. Most of that noise is aimed at Medicare Advantage and Part D prescription drug plans. But a growing number of beneficiaries—particularly those who enrolled in Medicare Advantage a few years ago and are now facing higher out-of-pocket costs as their health needs increase—are asking a different question: Should I drop my Advantage plan and switch to Original Medicare with a Medigap supplement instead? The answer is more complicated than most people realize, and the December 7 deadline is only part of the story.

First, let's be precise about what the Annual Enrollment Period (AEP), which runs October 15 through December 7 each year, actually covers. During AEP, you can switch from one Medicare Advantage plan to another, move from Medicare Advantage back to Original Medicare, switch Part D drug plans, or add a Part D plan if you don't have one. What AEP does not do is give you any special right to enroll in a Medigap policy. Medigap—also called Medicare Supplement insurance—is sold by private insurers and operates under a completely separate set of enrollment rules governed by both federal law and your state's insurance regulations. Confusing these two systems is one of the most expensive mistakes Medicare beneficiaries make.

Medigap policies are designed to fill the gaps that Original Medicare (Parts A and B) leaves behind. Original Medicare covers roughly 80% of approved medical costs after you meet your deductibles. In 2025, the Part A hospital deductible is $1,676 per benefit period—and there's no cap on how many benefit periods you can have in a year. The Part B deductible is $257 in 2025, and after that, you're responsible for 20% of all covered outpatient services with no out-of-pocket maximum. A serious illness or surgery can expose you to tens of thousands of dollars in cost-sharing under Original Medicare alone. Medigap plans—standardized by the federal government and sold under letter designations like Plan G, Plan N, and Plan F—are designed to cover most or all of those gaps, depending on which plan you choose.

Plan G is currently the most popular Medigap option for new enrollees, largely because Plan F (which covered the Part B deductible) was closed to people who became Medicare-eligible on or after January 1, 2020. Plan G covers the Part A deductible, skilled nursing facility coinsurance, Part B coinsurance and copayments, foreign travel emergency care (up to plan limits), and more—leaving you responsible only for the annual Part B deductible of $257. Monthly premiums for Plan G vary significantly by age, location, and insurer, but typically range from roughly $100 to $200 or more per month for a 65-year-old, rising with age. Plan N offers lower premiums in exchange for copays of up to $20 for office visits and up to $50 for emergency room visits, plus you're exposed to Part B excess charges in states that allow them. Comparing total annual cost—premiums plus likely out-of-pocket exposure—is the right way to evaluate these plans, not just the monthly premium.

Here's the critical issue that catches people off guard: unlike Medicare Advantage, Medigap policies sold outside of your guaranteed-issue window are subject to medical underwriting in most states. That means the insurance company can review your health history, charge you more based on pre-existing conditions, or outright deny your application. Your guaranteed-issue window—the period during which insurers must sell you any Medigap plan at standard rates regardless of your health—is the six-month period that begins the month you are both 65 or older and enrolled in Medicare Part B. If you enrolled in Part B at 65, that window opened then. If you delayed Part B because you had employer coverage, your window opens when you enroll in Part B. Once that six-month window closes, you generally lose guaranteed-issue protections unless a specific qualifying event applies to you.

This is where the December 7 deadline intersects with Medigap in a potentially costly way. If you use the AEP to disenroll from a Medicare Advantage plan and return to Original Medicare, your coverage change takes effect January 1. At that point, you may want to add a Medigap plan—but unless you have a qualifying Special Enrollment Period, you'll likely face medical underwriting. Federal law does provide a limited guaranteed-issue right when you leave a Medicare Advantage plan under certain conditions: specifically, if you enrolled in Medicare Advantage for the first time and disenroll within the first year, or if your plan is leaving your area or losing its Medicare contract. Simply deciding after several years that you prefer Original Medicare does not trigger a federal guaranteed-issue right for Medigap in most states.

There is an important exception worth knowing: the Medicare Advantage Open Enrollment Period (OEP), which runs January 1 through March 31 each year. During OEP, you can switch from one Medicare Advantage plan to another or drop Medicare Advantage and return to Original Medicare. However, the same underwriting caution applies—returning to Original Medicare during OEP does not automatically give you guaranteed-issue rights for Medigap unless you qualify under one of the specific federal or state protections.

State law can significantly expand your protections, and this is where geography matters enormously. A number of states have enacted birthday rules or other guaranteed-issue expansions that give beneficiaries additional windows to switch Medigap plans without medical underwriting. States with birthday rule protections—meaning you have a 30-day window around your birthday each year to switch to an equal or lesser Medigap plan without underwriting—include California, Idaho, Illinois, Kentucky, Louisiana, Maine, Maryland, Missouri, Nevada, New Jersey, New York, Oklahoma, and Oregon. New York and Connecticut go further, requiring guaranteed issue for Medigap year-round regardless of age or health status. If you live in one of these states, your options for switching or enrolling in Medigap are meaningfully broader than federal law alone provides. Check with your State Health Insurance Assistance Program (SHIP) counselor or your state insurance department to understand exactly what protections apply to you.

So who should seriously consider making the switch from Medicare Advantage to Original Medicare plus Medigap? The financial case tends to be strongest for people who are using significant healthcare services—those with chronic conditions, people who see multiple specialists regularly, or anyone who has hit or come close to their Medicare Advantage plan's out-of-pocket maximum (which can be as high as $9,350 for in-network services in 2025 under CMS limits). Medicare Advantage plans often have lower premiums and include extras like dental, vision, and gym memberships, but they also come with provider networks, prior authorization requirements, and cost-sharing structures that can add up quickly when you're actually sick. Original Medicare with a Plan G supplement, by contrast, gives you access to any provider who accepts Medicare nationwide—no network restrictions, no referrals required for specialists—with highly predictable annual costs.

The financial math deserves a concrete example. Suppose you're 70 years old and paying $0 in monthly premium for a Medicare Advantage plan, but your plan has a $5,000 in-network out-of-pocket maximum and you've been hitting $3,000 to $4,000 in cost-sharing most years due to ongoing health issues. A Plan G Medigap policy in your area might cost $150 per month, or $1,800 per year in premiums. Add the $257 Part B deductible and your maximum annual exposure under Plan G is roughly $2,057—compared to the $3,000 to $4,000 you've been paying under Advantage. Over five years, the difference can be substantial. Of course, if you're healthy and rarely use services, the Advantage plan's lower premium may serve you better. The right answer depends on your actual utilization, your health trajectory, and your risk tolerance.

If you're considering making this switch, the sequence of steps matters. First, confirm whether you have guaranteed-issue rights in your state before you disenroll from anything. Contact your SHIP counselor—free, unbiased counseling available in every state through the Medicare SHIP program—before making any changes. Second, if you do have underwriting risk, consider applying for a Medigap policy and getting approved before you disenroll from Medicare Advantage, so you know you have coverage lined up. Third, understand that if you return to Original Medicare, you'll also need a standalone Part D prescription drug plan unless your Medigap plan includes drug coverage (only older plans do). Failing to enroll in Part D when you first become eligible can result in a permanent late enrollment penalty of 1% of the national base beneficiary premium for every month you went without creditable coverage.

The December 7 deadline is real and important for Advantage and drug plan decisions. But for Medigap, the more important deadline may have been the month you turned 65—and if you missed that window, navigating your options now requires careful, state-specific guidance rather than a rushed decision before year-end. Take the time to understand your underwriting exposure, compare total annual costs honestly, and use the free resources available to you before making a change that could affect your healthcare finances for years to come.