If you’ve been thinking about trading your Medicare Advantage plan for original Medicare plus a Medigap supplement, there’s a rule you need to understand before you make the switch: medical underwriting. New research from KFF estimates that nearly three-quarters of Medicare Advantage enrollees could be denied a Medigap policy because of a pre-existing condition. In plain English, the door to a supplement plan may already be closing — and many seniors don’t find that out until it’s too late. Here’s what that means for your 2027 planning.

This isn’t a scare tactic. It’s a timing problem. Medigap rights are strongest when you’re brand new to Medicare and weakest after you’ve been on an Advantage plan for a while. Understanding that timeline is one of the most valuable pieces of financial planning a senior can do.

What Medical Underwriting Actually Means

When you first enroll in Medicare Part B at age 65, you get a six-month Medigap Open Enrollment Period. During those six months, insurance companies selling Medigap policies in most states cannot ask you about your health, cannot charge you more because of a past diagnosis, and cannot deny you coverage. It’s the single best window you will ever have to lock in a supplement plan.

Once that window closes, the rules change. Outside of a handful of protected situations, a Medigap insurer in most states can review your medical history — your heart condition, your diabetes, your cancer remission, your COPD, even some prescription medications — and decide whether to accept you, charge you a higher premium, or decline you outright. That process is called medical underwriting.

This is the crux of the KFF finding. People who joined Medicare Advantage are often healthy at 65 and choose the lower-premium route. Years later, when they want to move to original Medicare with a supplement, they’re no longer a blank medical slate. The underwriting door has narrowed, and for many it has shut.

Why Medicare Advantage Enrollees Face the Steepest Climb

There are three reasons Advantage members are especially exposed:

1. Trial rights are limited. Federal law gives you a guaranteed right to buy a Medigap policy if you try Medicare Advantage for the first time and disenroll within the first 12 months. Miss that window and the guarantee disappears in most states.

2. Time works against you. The longer you’re on an Advantage plan, the more likely you are to have received a diagnosis or started a medication that an underwriter will flag. KFF’s analysis found the large majority of Advantage enrollees have at least one condition that could trigger a denial.

3. State rules vary dramatically. A handful of states — including New York, Connecticut, Massachusetts, and Maine — require year-round guaranteed issue or community-rated Medigap premiums, meaning you can switch regardless of health. If you live in one of those states, you have far more flexibility. If you don’t, your options are limited to protected enrollment situations.

The Protected Situations That Still Open the Door

You may still have a guaranteed right to buy a Medigap policy — no underwriting — in these situations:

• You’re in your initial six-month Medigap Open Enrollment Period.
• You’re within the first 12 months of joining a Medicare Advantage plan and want to switch back.
• Your Medicare Advantage plan leaves your service area or ends its contract with Medicare.
• Your employer or union group health coverage ends.
• You move to an area where your current Medigap plan isn’t offered.
• Certain other limited federal protections apply, such as if your Medigap insurer goes bankrupt.

Outside of these, you’re relying on the insurer’s willingness to accept you — and on state law.

How to Choose: A Practical Medigap Checklist

If you’re deciding whether to move to a supplement for 2027, work through this list before you call a single insurer:

Know your state’s rules. Confirm whether your state guarantees Medigap issuance year-round or permits underwriting. This single fact changes your entire strategy.

Check your current health honestly. List every diagnosis, every ongoing prescription, and every recent treatment. Underwriters will see it all.

Compare the right plans. In most states, Plans G, N, and the high-deductible versions of F and G offer the strongest balance of comprehensive coverage and premium value for new enrollees. Plan F is closed to people who became eligible for Medicare after January 1, 2020.

Look at more than the premium. Ask about rate increase history, not just today’s price. A cheap premium from an insurer with a history of steep increases can cost far more over ten years.

Act during your protected window. If you’re still inside your initial Medigap Open Enrollment Period or your 12-month Advantage trial right, don’t wait. These windows do not reopen.

What This Means for Your 2027 Decision

The KFF findings aren’t a reason to panic — they’re a reason to plan. If you’re currently on Medicare Advantage and in good health, this is the moment to weigh whether you want the long-term flexibility of original Medicare plus a supplement. If you wait until a diagnosis arrives, the choice may be made for you.

Conversely, if you’re happy with your Advantage plan and it covers your doctors and medications well, stay put with confidence. The lesson isn’t that one path is always better. The lesson is that your health today is an asset you can only spend once, and Medigap underwriting rules reward people who decide early.

Seniors in Minnesota, Oregon, and other states facing 2027 plan disruptions — where hundreds of thousands are losing or changing Medicare Advantage coverage — should pay particular attention. A plan exit can create a guaranteed-issue right, but those rights are narrow and time-limited. Know your deadline before it passes.

Get Personalized Medigap Quotes Today

Every state, every ZIP code, and every health history is different — which is exactly why a generic answer won’t help you. Before your protected enrollment window closes, take ten minutes to compare real plans side by side.

Visit medigapplanfinders.com for free, no-obligation Medigap quotes. Enter your ZIP code, see the plans available where you live, and compare premiums, coverage, and insurer ratings in one place. It costs nothing to look — and it could save you thousands while keeping your choice open.

Sources: KFF, “Nearly Three-Quarters of Medicare Advantage Enrollees Could be Denied a Medigap Policy Due to a Pre-Existing Condition” and “Key Facts About Medigap Enrollment and Premiums for Medicare Beneficiaries.”