Every year, thousands of seniors consider switching from Medicare Advantage back to Original Medicare, often drawn by broader provider access and the freedom to see any doctor who accepts Medicare. But there is a hidden trap that many discover too late: Medigap plans, also called Medicare Supplement plans, are not guaranteed-issue in most situations. If you miss the right window or have certain health conditions, you can be denied coverage outright — or charged significantly more than your neighbor who enrolled at the right time.

As KFF Health News recently reported, Medigap plan refusals are a growing concern for seniors making the leap from Advantage plans. With Medicare Advantage enrollment hitting new highs in 2026, more beneficiaries than ever face this crossroads. Understanding the rules — and the risks — could save you hundreds of dollars a month and prevent you from getting stuck without the coverage you need.

Medigap Guaranteed-Issue Rights: The Window You Cannot Afford to Miss

When you first enroll in Medicare Part B at age 65, you enter a six-month Medigap Open Enrollment Period. During this window, insurance companies cannot deny you any Medigap policy, cannot charge you more based on your health history, and cannot make you wait for pre-existing conditions to be covered. This is the single most important enrollment window in Medicare, and it only happens once.

If you enrolled in a Medicare Advantage plan during your initial enrollment period instead, you may still have a brief chance to switch to Original Medicare with Medigap protections — but the rules are narrow, and the timing is strict. For example, if you joined an Advantage plan when first eligible, you have a 12-month “trial right” to switch to a Medigap plan. After that trial period ends, you generally lose guaranteed-issue protections unless you qualify for a special circumstance.

The takeaway? If you are considering switching from Medicare Advantage to Original Medicare, do not wait. Check whether you are still within your trial right period or a Special Enrollment Period that triggers Medigap protections. Waiting even a few months past that window could close the door permanently.

Why Medigap Plans Can Deny You (And How Often It Happens)

Unlike Medicare Advantage plans, which must accept anyone who is eligible for Medicare during designated enrollment periods, Medigap plans are private insurance products subject to medical underwriting. Once you are outside a guaranteed-issue window, insurers can review your health history and decide whether to accept you — and at what price.

Common reasons for Medigap denial include pre-existing conditions such as diabetes, heart disease, recent surgeries, or ongoing cancer treatment. In some cases, even high cholesterol or controlled high blood pressure can trigger a premium surcharge. According to the KFF Health News report, refusals are not rare — they are a standard practice among Medigap carriers, and the denial rate rises significantly with age and health complexity.

What does this mean in dollars and cents? A Woman’s World report highlighted that making the wrong Medicare enrollment choice could cost seniors an extra $200 to $300 per month. That is the difference between a standard Medigap premium and a medically underwritten plan — or worse, being stuck with no supplement plan at all, facing Original Medicare’s 20% coinsurance with no cap on out-of-pocket costs.

The 2026 Landscape: More Seniors at Risk Than Ever

Medicare Advantage enrollment now accounts for more than half of all Medicare beneficiaries, according to KFF trends data for 2026. While Advantage plans often offer low or zero-dollar premiums, they come with network restrictions, prior authorizations, and limited provider access that can become frustrating — especially as health needs grow more complex.

The problem is that many seniors who joined Advantage plans during their initial enrollment are now several years past their Medigap trial right window. As they age and encounter more health issues, the desire to switch to Original Medicare with a Medigap plan grows — but their health history makes Medigap approval increasingly difficult. It is a classic catch-22: you need the coverage most when your health makes it hardest to get.

Adding to the complexity, Medigap premiums have been rising steadily. US News recently named the best Medigap plans of 2026, but the prices vary dramatically by carrier, state, and even zip code. Plan G — the most popular Medigap plan — can range from $120 to over $300 per month depending on where you live and when you enroll. The key is locking in the lowest rate while you still have guaranteed-issue protections.

Which States Offer Extra Protections? (And Which Do Not)

Federal Medigap protections only apply during your initial six-month Open Enrollment Period and under specific, limited circumstances. However, some states have enacted their own laws that provide additional guaranteed-issue rights for seniors switching from Medicare Advantage to Original Medicare.

States like Connecticut, Massachusetts, Maine, New York, and Vermont have year-round Medigap guaranteed-issue protections, meaning insurers cannot deny coverage or charge more based on health status regardless of when you enroll. California, Oregon, and Washington offer more limited but still meaningful protections during certain windows. The vast majority of states, however, follow federal rules only — meaning if you miss your window, you are at the mercy of medical underwriting.

If you live in a state without extra protections, your planning needs to be even more careful. Do not assume you can switch later — the decision to enroll in Medicare Advantage versus Original Medicare with a Medigap plan is often irreversible in practical terms once your health changes.

How to Protect Yourself: A Practical Plan

Here is a straightforward checklist to help you avoid Medigap denial and costly mistakes:

1. Know your Medigap Open Enrollment window. It begins the first day of the month you are both 65 and enrolled in Part B. Mark it on your calendar. Do not let it pass without evaluating your options.

2. If you are in an Advantage plan and thinking about switching, act quickly. If you are still within your first 12 months, you may have a trial right to switch. Research your state rules and call a licensed agent who specializes in Medicare supplements.

3. Compare plans before you leave your current coverage. Get Medigap quotes from multiple carriers. Prices for the same exact Plan G or Plan N can differ by hundreds of dollars between insurers in the same zip code.

4. Consider a Medigap plan even if you are healthy today. The whole point of Medigap is protecting you against future health costs. You do not buy fire insurance when your house is already burning down — buy it while you can.

5. Work with a knowledgeable agent. A Medicare broker who represents multiple carriers can help you navigate the guaranteed-issue rules, compare premiums, and find a plan that fits your budget. There is no cost to you — agents are paid by the insurance companies.

Conclusion: Make the Move While You Still Can

The freedom of Original Medicare combined with a Medigap plan is unmatched when it comes to choice of doctors and predictable out-of-pocket costs. But that freedom comes with a deadline. Once your guaranteed-issue window closes, the door to Medigap may never open as wide again.

If you are considering your Medicare options — whether you are turning 65 soon, already in an Advantage plan, or helping a loved one navigate their choices — do not wait until a health crisis forces your hand. Compare Medigap plans today while you still have the protections that come with guaranteed-issue rights.

At MedigapPlanFinders.com, we make it easy to compare Medicare Supplement plans from top-rated carriers in your area. Get free, no-obligation quotes and see exactly what you would pay — before you make a decision that could cost you hundreds of dollars more each month. Click here to compare plans now »