Original Medicare is a strong foundation — but it is not complete coverage. Part A and Part B together leave you responsible for deductibles, coinsurance, and copayments that can add up quickly, especially if you have a serious illness or frequent medical needs. Medicare Supplement plans, also called Medigap, are designed to fill those gaps.

Here is what you need to know before you choose one.

What Is a Medicare Supplement Plan?

A Medicare Supplement plan is private health insurance that works alongside Original Medicare (Parts A and B). It does not replace Medicare — it pays after Medicare pays, covering some or all of the costs that Medicare leaves behind.

These plans are standardized by the federal government. That means a Plan G from one insurance company covers exactly the same benefits as a Plan G from any other company. The only difference between carriers is the monthly premium and the quality of customer service.

What Gaps Does Original Medicare Leave?

Before understanding what Medigap covers, it helps to understand what Original Medicare does not cover:

Part A gaps:

• Hospital deductible ($1,676 per benefit period in 2026)
• Daily coinsurance for extended hospital stays (days 61–90 and beyond)
• Skilled nursing facility coinsurance (days 21–100)
• No out-of-pocket maximum

Part B gaps:

• Annual deductible ($257 in 2026)
• 20% coinsurance on all covered outpatient services — with no cap
• Excess charges from providers who do not accept Medicare assignment

That 20% coinsurance with no ceiling is the biggest risk. A $100,000 surgery leaves you with a $20,000 bill under Original Medicare alone. A Medigap plan eliminates or sharply reduces that exposure.

The Most Popular Plans: G and N

There are ten standardized Medigap plans (A, B, D, G, K, L, M, N, and two high-deductible versions). In practice, two plans dominate new enrollments for most retirees: Plan G and Plan N.

Medicare Supplement Plan G

Plan G is the most comprehensive Medigap plan available to new Medicare enrollees. It covers:

• Part A deductible
• Part A coinsurance and hospital costs (up to an additional 365 days after Medicare benefits are exhausted)
• Part A hospice care coinsurance or copayment
• Skilled nursing facility coinsurance
• Part B coinsurance or copayment (the full 20%)
• Part B excess charges
• Foreign travel emergency (80%, up to plan limits)

The only gap Plan G does not cover is the Part B annual deductible ($257 in 2026). After you meet that deductible once per year, Plan G pays 100% of Medicare-approved costs for the rest of the year.

For retirees who want predictable, near-zero out-of-pocket costs, Plan G is the gold standard.

Medicare Supplement Plan N

Plan N covers everything Plan G covers — except Part B excess charges — and adds two small cost-sharing elements:

• Up to a $20 copay for office visits
• Up to a $50 copay for emergency room visits that do not result in inpatient admission

In exchange for accepting those modest copays, Plan N typically carries a lower monthly premium than Plan G — sometimes $30–$60 less per month depending on your age and the carrier.

Plan N is a strong choice if you are generally healthy, see your doctor a few times a year, and want to trade a slightly lower premium for modest cost-sharing.

Which Is Better — G or N?

There is no universal answer. The right choice depends on:

• How often you use medical care. Frequent doctor visits make Plan G's higher premium worthwhile. If you rarely see a provider, Plan N's lower premium may save you more over time.
• Whether your doctors accept Medicare assignment. If they do, excess charges are not a concern and Plan N's exclusion of that benefit does not matter.
• Your risk tolerance. Plan G offers a hard ceiling on out-of-pocket costs. Plan N introduces small, variable copays.

An independent broker can run the numbers for your specific situation and the plans available in your zip code.

How Medigap Differs from Medicare Advantage

This is one of the most common points of confusion in Medicare planning.

Medicare Supplement (Medigap) works with Original Medicare. You keep your Medicare card, see any doctor or specialist in the country who accepts Medicare, and your Medigap plan pays the gaps. There are no networks, no referrals, and no prior authorizations for Medicare-covered services.

Medicare Advantage replaces Original Medicare with a private plan. These plans often have lower premiums — sometimes $0 — but they use provider networks, require referrals in some cases, and have their own cost-sharing structures including copays, coinsurance, and an annual out-of-pocket maximum.

Neither is universally better. Medigap tends to suit retirees who travel frequently, have established specialist relationships, or want maximum coverage certainty. Medicare Advantage may suit healthier retirees who prefer lower premiums and are comfortable with a network.

When Can You Enroll in a Medigap Plan?

Timing matters significantly with Medicare Supplement plans.

Open Enrollment Period: When you first enroll in Medicare Part B, you have a six-month window during which insurance companies must sell you any Medigap plan at standard rates — regardless of your health history. This is your strongest enrollment right, and it does not repeat.

Outside Open Enrollment: After your initial window closes, insurers in most states can use medical underwriting. That means they can charge you more, exclude pre-existing conditions, or deny coverage altogether based on your health history.

Missouri does not have a continuous open enrollment law for Medigap, so your initial enrollment window is especially important. If you miss it, you may still qualify through a Guaranteed Issue Right — a federal protection that applies in specific situations such as losing employer coverage or leaving a Medicare Advantage plan.

What Medigap Does Not Cover

Even the most comprehensive Medigap plan has limits. No Medigap plan covers:

• Prescription drugs — you need a separate Part D plan
• Dental, vision, and hearing — not covered by Medicare or Medigap
• Long-term care — custodial care in a nursing home is not a Medicare benefit
• Routine eye exams or eyeglasses

Many retirees pair a Medigap plan with a standalone Part D drug plan and a dental/vision/hearing plan to build more complete coverage.

How Premiums Are Priced

Medigap premiums vary by carrier, your age, your location, and the pricing method the insurer uses:

• Community-rated: Everyone pays the same premium regardless of age. Premiums may increase over time due to inflation but not because you are getting older.
• Issue-age-rated: Your premium is based on your age when you first enroll and does not increase as you age (though it may increase for other reasons).
• Attained-age-rated: Your premium starts lower but increases as you age. These plans are often the least expensive at enrollment but the most expensive over time.

Understanding the pricing method is as important as comparing the initial premium. A plan that looks affordable at 65 may become a burden at 75 if it uses attained-age pricing.

Choosing a Carrier: What Actually Differs

Since benefits are standardized, the meaningful differences between carriers come down to:

• Monthly premium — shop multiple carriers for the same plan letter
• Premium increase history — some carriers have a track record of stable rates; others raise premiums aggressively
• Financial strength ratings — look for carriers rated A or better by AM Best
• Customer service — claims processing speed and ease of reaching a representative

An independent broker has access to multiple carriers and can compare all of these factors side by side — something a single-carrier agent or a direct enrollment website cannot do.

Talk to a Local Medicare Expert

Choosing a Medigap plan is one of the most consequential Medicare decisions you will make. The plan you select at 65 can follow you for decades, and switching later may require medical underwriting.

James Hughes is an independent Medicare broker serving retirees across Missouri. He works with multiple carriers, has no incentive to favor one plan over another, and offers free consultations with no obligation to enroll.

Call 314-229-6146 or visit the Contact page to schedule your free Medicare review.