Medicare Supplement (Medigap) Plans Explained
Original Medicare covers a lot — but not everything. The gaps it leaves behind, including deductibles, coinsurance, and copayments, can add up quickly, especially for people who use healthcare regularly. That's where Medicare Supplement insurance, commonly called Medigap, comes in.
Here's what these plans actually are, how they work, and what you'd need to think through to evaluate whether one makes sense for your situation.
What Is a Medigap Plan?
A Medigap plan is private health insurance sold specifically to people enrolled in Original Medicare (Parts A and B). These plans are designed to cover some or all of the out-of-pocket costs that Medicare doesn't pay — things like hospital coinsurance, skilled nursing facility costs, and the Part B deductible (depending on the plan).
A few important things to understand right away:
- Medigap plans work alongside Original Medicare — they don't replace it.
- They are not the same as Medicare Advantage (Part C), which is an alternative way to receive Medicare benefits through a private insurer.
- You must be enrolled in both Medicare Part A and Part B to purchase a Medigap plan.
- Medigap plans do not cover prescription drugs — for that, you'd need a separate Part D plan.
How Medigap Plans Are Standardized
In most states, Medigap plans are federally standardized, meaning a Plan G from one insurance company offers the same basic benefits as a Plan G from another. What differs between insurers is the premium you pay and the quality of customer service.
Plans are labeled with letters — currently A, B, D, G, K, L, M, and N are available to most new enrollees. (Plans C and F, which covered the Part B deductible, are no longer available to people who became eligible for Medicare on or after January 1, 2020.)
What Different Plans Cover
The plans vary in how comprehensively they fill Medicare's gaps. Here's a simplified comparison of the most widely purchased options:
| Plan | Part A Coinsurance | Part B Coinsurance | Part B Deductible | Skilled Nursing Facility Coinsurance | Foreign Travel Emergency |
|---|---|---|---|---|---|
| Plan A | ✅ | ✅ | ❌ | ❌ | ❌ |
| Plan G | ✅ | ✅ | ❌ | ✅ | ✅ |
| Plan N | ✅ | Partial* | ❌ | ✅ | ✅ |
| Plan K | ✅ | 50% | ❌ | 50% | ❌ |
| Plan L | ✅ | 75% | ❌ | 75% | ❌ |
*Plan N covers Part B coinsurance except for certain office and emergency room visits, where copays may apply.
Plan G is currently one of the most comprehensive options available to new enrollees, while Plan N typically carries a lower premium in exchange for some cost-sharing at the point of service. Plans K and L have lower premiums but only cover a percentage of costs until an annual out-of-pocket limit is reached.
How Medigap Pricing Works
Even though benefits are standardized by plan letter, premiums vary significantly based on several factors:
- Age — most insurers use one of three pricing methods: community-rated (same premium for all ages), issue-age-rated (based on your age when you first buy), or attained-age-rated (increases as you age)
- Location — premiums vary considerably by state and even by county
- Gender — some states allow gender-based pricing; others prohibit it
- Tobacco use — smokers often pay higher premiums
- Household discounts — some insurers offer discounts if another household member also has a policy with them
- Insurer — two companies can offer the identical plan letter at meaningfully different price points
Because of this variation, comparing premiums for the same plan letter across multiple insurers in your area is one of the most practical steps you can take.
When You Can Buy a Medigap Plan: Enrollment and Timing Matter 🕐
This is one of the most critical pieces of the Medigap puzzle. When you first become eligible for Medicare and enroll in Part B, you enter a 6-month Medigap Open Enrollment Period. During this window, insurers cannot deny you coverage or charge you more based on pre-existing health conditions.
Outside of this window, insurers in most states can use medical underwriting — meaning they can review your health history and potentially:
- Charge you a higher premium
- Exclude coverage for certain conditions
- Decline your application entirely
There are some exceptions called guaranteed issue rights — situations (such as losing employer coverage or a Medicare Advantage plan leaving your area) that give you a protected right to buy certain Medigap plans regardless of health status. But these situations are specific and limited.
The general principle: the earlier you enroll during your open enrollment window, the more protected you are.
Medigap vs. Medicare Advantage: The Core Trade-Off
These are two fundamentally different paths, and understanding the distinction is essential.
| Factor | Medigap + Original Medicare | Medicare Advantage |
|---|---|---|
| Network flexibility | See any doctor who accepts Medicare, nationwide | Usually restricted to a plan network |
| Monthly premium | Higher (Medigap premium + Part B premium) | Often lower (some plans have $0 premium beyond Part B) |
| Predictability of costs | High — fewer surprises at point of care | Varies — copays and cost-sharing at each service |
| Extras (dental, vision, etc.) | Not included | Often bundled |
| Switching rules | Harder to switch later due to underwriting | Annual enrollment opportunity |
Neither path is objectively better. People who travel frequently, see specialists often, or highly value predictable costs tend to find Medigap appealing. People who want lower monthly premiums and are comfortable with network-based care often find Medicare Advantage more practical. Your health status, financial situation, and how you use healthcare all shape which structure fits better.
What to Evaluate Before You Decide
Before choosing a Medigap plan — or deciding whether to get one at all — the factors most worth examining include:
- How often you use healthcare, and whether you prefer predictable costs or are comfortable with some variability
- Whether you travel domestically or internationally (some plans include foreign travel emergency coverage)
- Your current and anticipated health needs, including any specialists or facilities you want access to
- The premium spread between plan letters in your area, and how that compares to the potential out-of-pocket exposure you'd carry without supplemental coverage
- Which pricing method your prospective insurer uses — attained-age pricing can lead to significant premium increases over time
- Your state's specific rules, since some states have additional consumer protections around Medigap
Because the right answer depends heavily on your individual health profile, financial picture, and how you use the healthcare system, many people find it useful to work through these questions with a licensed Medicare counselor or a State Health Insurance Assistance Program (SHIP) advisor — a free, unbiased resource available in every state.
