Medicare Medigap Explained: How It Works and What It Really Covers

If you’re enrolled in Original Medicare (Parts A and B), you may notice that it doesn’t pay for everything. That’s where Medicare Supplement Insurance, commonly called Medigap, comes in.

This guide breaks down what Medigap is, how it works with Medicare, what it does and does not cover, and how people typically decide whether it fits their needs.

What Is Medigap?

Medigap is private health insurance designed to “fill the gaps” in Original Medicare coverage.

Original Medicare helps pay for many health care services, but you still have:

• Deductibles
• Coinsurance
• Copayments
• Certain services not covered at all

A Medigap policy helps pay some of these out-of-pocket costs. In other words, Medicare pays its share of approved charges first, then your Medigap plan may pay part or all of the remaining share (depending on the plan you choose).

Key point:
Medigap is not a separate type of Medicare coverage like Medicare Advantage. It’s extra insurance that works alongside Original Medicare.

How Medigap Works With Original Medicare

To buy a Medigap policy, you must be enrolled in:

• Medicare Part A (hospital insurance), and
• Medicare Part B (medical/doctor insurance)

Here’s the typical sequence when you get care:

1. You visit a doctor or hospital that accepts Medicare.
2. Medicare pays its portion of the approved amount.
3. Your Medigap plan pays some or all of the remaining cost (depending on your policy).
4. You pay any leftover amount that Medicare and Medigap do not cover.

Medigap is designed to make your costs more predictable, especially if you see doctors frequently or want protection from large unexpected bills.

Medigap vs. Medicare Advantage: What’s the Difference?

Many people compare Medigap with Medicare Advantage, but they are very different options.

Medigap (Medicare Supplement)

• Works with Original Medicare
• You keep Medicare Parts A and B
• Generally lets you see any provider that accepts Medicare
• Focuses on covering out-of-pocket costs (deductibles, coinsurance, copays)
• Sold by private insurance companies as standardized plans

Medicare Advantage (Part C)

• An alternative to Original Medicare
• Combines Part A and Part B, often includes Part D (drug coverage)
• Often uses networks (HMOs, PPOs)
• May include extra benefits (varies by plan)
• You generally cannot have Medigap and Medicare Advantage at the same time

Bottom line:
Medigap supplements Original Medicare; Medicare Advantage replaces it for your medical coverage. Consumers typically choose one path or the other, not both.

Standard Medigap Plans: Plan Letters and What They Mean

Medigap policies are standardized in most states. That means a Plan G from one insurer generally offers the same basic benefits as a Plan G from another insurer, although monthly premiums may differ.

Common standardized Medigap plans include:
Plan A, B, C, D, F, G, K, L, M, and N

Note: Some plans, such as Plan C and Plan F, are not available to people who became newly eligible for Medicare after certain dates. Availability can depend on when you first qualified for Medicare and where you live.

At a Glance: What Medigap Plans Typically Help Cover

While details vary by plan letter, Medigap policies often help with:

• Part A coinsurance and extra hospital days
• Part B coinsurance or copayments
• Skilled nursing facility coinsurance
• Part A deductible
• In some plans, the Part B deductible (not available to newer enrollees)
• Foreign travel emergency care (limited, in some plan types)

Here is a simplified view of how Medigap fits with Original Medicare:

*Exact coverage depends on the plan letter (A, G, N, etc.) you choose.

What Medigap Does Not Cover

Medigap does not pay for everything. It usually does not cover:

• Prescription drugs (outpatient medications)
• Routine dental, vision, or hearing services
• Long-term care or custodial care (help with daily activities)
• Private-duty nursing
• Services not covered by Medicare at all (with limited Medigap exceptions like some foreign travel emergency coverage)

To get help with prescription drugs, most people pair their Medigap policy with a standalone Medicare Part D drug plan.

When Can You Buy Medigap? Enrollment Basics

Your timing can heavily affect your options and costs.

Medigap Open Enrollment Period

Your Medigap Open Enrollment Period is a one-time, 6‑month window that:

• Begins the first month you are 65 or older, and
• Enrolled in Medicare Part B

During this period:

• You generally have the widest choice of Medigap plans available in your area.
• You usually cannot be charged more or denied coverage because of health conditions.

Many people find this to be the easiest time to get Medigap coverage.

Buying Medigap After Your Open Enrollment

After your open enrollment window ends:

• You may still apply for a Medigap plan, but
• The insurance company may use medical underwriting, which can affect:
  • Whether they accept your application
  • The premium you pay

There are certain situations, often called “guaranteed issue rights” or “Medigap protections,” where companies must offer Medigap coverage without using health underwriting. Examples may include:

• Losing certain types of health coverage through no fault of your own
• Your Medicare Advantage plan leaving your service area

The specific rules and situations depend on federal and state regulations.

How Much Does Medigap Cost?

With Medigap, you usually pay:

• Your monthly Part B premium to Medicare
• A monthly premium to your Medigap insurance company
• A monthly premium to a Part D drug plan (if you enroll in one)

Medigap premiums can vary based on:

• Plan letter (A, G, N, etc.)
• Insurance company
• How the plan is priced (rating method)
• Where you live
• When you enroll and sometimes your age and health (where underwriting is used)

Many people find that while they pay more in monthly premiums, they may pay less at the point of care, or have more predictable costs, compared with relying on Original Medicare alone.

Who Typically Considers Medigap?

People often look into a Medigap policy if they:

• Want the flexibility to see any provider who accepts Medicare
• Prefer fewer surprise bills and more predictable out-of-pocket costs
• Travel frequently within the U.S. and want a wide choice of doctors and hospitals
• Value keeping Original Medicare instead of switching to a network-based plan

On the other hand, some people decide against Medigap if they:

• Prefer a lower monthly premium, even if that means paying more out of pocket when they get care
• Are comfortable with network-based Medicare Advantage plans that bundle coverage, sometimes including drug coverage and extra benefits

The “right” choice depends on your budget, how often you use medical care, and how important provider flexibility and cost predictability are to you.

Key Terms to Know

Understanding a few basic terms can make Medigap much clearer:

• Premium – The amount you pay each month for your Medigap policy.
• Deductible – The amount you pay for covered services before insurance starts to pay.
• Coinsurance – Your share of the cost of a covered service, usually a percentage (for example, 20%).
• Copayment (copay) – A fixed dollar amount you pay for a covered service.
• Guaranteed renewable – Medigap policies are usually guaranteed renewable as long as you pay your premium, meaning the insurer generally cannot cancel your policy due to health changes.

Simple Step-By-Step: How to Approach Medigap

If you are considering Medigap, many people find this process helpful:

1. Confirm your Medicare status

   • Make sure you are enrolled in Part A and Part B.

2. Decide between Medigap and Medicare Advantage

   • You generally choose one approach for your coverage.

3. Compare Medigap plan letters

   • Review what each standardized plan (A, G, N, etc.) typically covers.
   • Focus on how much protection you want against deductibles and coinsurance.

4. Check your Medigap Open Enrollment timing

   • If you’re in your 6-month Medigap open enrollment, you may have more options.

5. Estimate total costs

   • Consider premiums + expected out-of-pocket costs, not just premiums alone.

6. Add prescription drug coverage if needed

   • Most people pair Medigap with a Medicare Part D plan to help with medications.

Quick Recap: What Is Medicare Medigap?

Medicare Medigap is:

• Supplemental insurance offered by private companies
• Designed to help pay out-of-pocket costs not fully covered by Original Medicare
• Standardized into plan letters, each with a defined set of benefits
• Typically used by people who want provider flexibility and more predictable costs

It is not Medicare Advantage, and it does not replace Medicare Parts A and B—rather, it works alongside them.

Understanding these basics can help you compare your options more confidently and choose the kind of Medicare coverage that best fits your health care needs, budget, and preferences.