Original Medicare covers 80% of your outpatient and preventive care costs — but that remaining 20% coinsurance can add up fast, especially if you have frequent doctor visits, specialist appointments, or ongoing treatments. There’s no annual cap on that 20%, which means your out-of-pocket costs have no ceiling under Original Medicare alone.
That’s where Medigap (Medicare Supplement Insurance) comes in. Medigap plans are sold by private insurers and are designed to fill the “gaps” that Original Medicare doesn’t cover—including that dreaded 20% coinsurance.
This guide walks you through which Medigap plans cover your 20% coinsurance, how they work, what they cost, and how to choose the right one for your situation.
What Is the Medicare Part B 20% Coinsurance?
Every time you visit a doctor, see a specialist, get lab work, or receive outpatient care under Medicare Part B, Medicare pays 80% of its approved amount. You’re responsible for the remaining 20%—with no limit on how much that adds up to over a year.
Examples of services subject to the 20% Part B coinsurance:
- Primary care and specialist office visits
- Outpatient surgery
- Durable medical equipment (DME)
- Diagnostic tests and lab work
- Mental health services
- Ambulance services (in some cases)
- Physical therapy and rehabilitation
If you have frequent medical needs, that 20% can become a significant financial burden. Medigap is specifically designed to protect you from these open-ended costs.
Which Medigap Plans Cover the 20% Coinsurance?
Medigap plans are labeled by letters: A, B, C, D, F, G, K, L, M, and N. Not all plans are available in every state, and each covers a different set of gaps. Here’s how they break down when it comes to your Part B coinsurance:
Plans That Cover the Part B 20% Coinsurance in Full
| Plan | Part B Coinsurance Coverage | Part B Excess Charges | Notable Features |
|---|---|---|---|
| Plan A | Yes—100% | No | Most basic plan; required to be offered by all insurers |
| Plan B | Yes—100% | No | Similar to A, adds Part A deductible coverage |
| Plan C | Yes—100% | No | Comprehensive but no longer available to new Medicare beneficiaries (effective Jan 1, 2020) |
| Plan D | Yes—100% | No | Covers most gaps; doesn’t cover Part B excess |
| Plan F | Yes—100% | Yes—100% | Most comprehensive; no longer available to new Medicare beneficiaries (effective Jan 1, 2020) |
| Plan G | Yes—100% | Yes—100% | Most popular plan for new beneficiaries; covers everything except the Part B deductible |
| Plan N | Yes—100% (except for a $20 copay for office visits and $50 for the ER). | No | Lower premium option with some cost-sharing |
Plans That Cover Only a Portion of the 20% Coinsurance
| Plan | Part B Coinsurance Coverage | Other Notes |
|---|---|---|
| Plan K | 50% of Part B coinsurance | Lower premium; higher out-of-pocket limit ($7,060 in 2024) |
| Plan L | 75% of Part B coinsurance | Mid-range premium and out-of-pocket limit ($3,530 in 2024) |
Note: Plans C and F are no longer available to Medicare beneficiaries who became eligible for Medicare on or after January 1, 2020. If you were eligible before that date, you may still be able to purchase them. Plan G is widely considered the best alternative for new beneficiaries seeking comprehensive coverage.
Plan G: The Most Popular Choice for Covering the 20% Coinsurance
Medigap Plan G has become the go-to plan for Medicare beneficiaries who want:
- 100% coverage of the Part B 20% coinsurance
- 100% coverage of Part B excess charges (if your provider doesn’t accept Medicare assignment)
- Coverage for Part A hospital deductible
- Coverage for skilled nursing facility care coinsurance
- Coverage for foreign travel emergency care (up to plan limits)
The only gap Plan G doesn’t cover is the Part B annual deductible (which is $240 in 2024 and changes annually). This makes it easy to predict your costs: you pay the deductible once per year, and then Medigap Plan G covers everything else Medicare doesn’t.
Plan N: A Lower-Premium Alternative
Medigap Plan N covers the Part B 20% coinsurance but includes some cost-sharing to keep monthly premiums lower:
- Office visits: $20 copay (waived if admitted to the hospital)
- Emergency room visits: $50 copay (waived if admitted as inpatient)
- Part B excess charges: NOT covered—if you see a provider who doesn’t accept Medicare assignment, you pay those charges yourself
Plan N is a good fit for healthy beneficiaries who don’t expect frequent doctor visits and want to keep monthly premiums affordable while still protecting against the big 20% bills.
Comparing Medigap Plans: Quick Reference
| Medigap Benefit | A | B | D | G | K | L | N |
|---|---|---|---|---|---|---|---|
| Part B Coinsurance (20%) | ✔ | ✔ | ✔ | ✔ | 50% | 75% | ✔* |
| Part A Hospital Coinsurance | ✔ | ✔ | ✔ | ✔ | 50% | 75% | ✔ |
| Part A Deductible | No | ✔ | ✔ | ✔ | 50% | 75% | ✔ |
| Skilled Nursing Coinsurance | No | No | ✔ | ✔ | 50% | 75% | ✔ |
| Part B Excess Charges | No | No | No | ✔ | No | No | No |
| Foreign Travel Emergency | No | No | ✔ | ✔ | No | No | ✔ |
| Out-of-Pocket Limit | No | No | No | No | $7,060 | $3,530 | No |
*Plan N covers Part B coinsurance except for a $20 office visit copay and a $50 ER copay.
How Much Do Medigap Plans That Cover the 20% Coinsurance Cost?
Medigap premiums vary widely based on several factors:
- Age: Most plans use age-based pricing (younger = lower premium)
- Location: Premiums differ significantly by state and ZIP code
- Gender and tobacco use: Can affect pricing
- Carrier: Different insurance companies charge different rates for identical coverage
As a general estimate (for a 65-year-old non-tobacco user in a mid-range area):
| Plan | Estimated Monthly Premium Range |
|---|---|
| Plan A | $100 – $250 |
| Plan B | $130 – $300 |
| Plan G | $150 – $400 |
| Plan N | $100 – $300 |
| Plan K (50% coverage) | $70 – $180 |
| Plan L (75% coverage) | $90 – $220 |
Important: These are estimates. Always get a personalized quote for your specific location and circumstances. Also note that Plan G and Plan N premiums are typically lower than Plan F because they don’t cover the Part B deductible — but they still cover the 20% coinsurance in full.
How to Choose the Right Medigap Plan
Ask yourself these questions:
- How often do you see doctors or specialists? If you have frequent appointments, covering the 20% in full (Plan G) saves you the most money long-term.
- Do you travel internationally? Plans G, D, and N include foreign travel emergency coverage—Plans A and B do not.
- Do your doctors accept Medicare assignment? If you see providers who don’t, Plan G’s coverage of Part B excess charges is valuable protection.
- Are you healthy with few expected medical visits? Plan N’s lower premium with some cost-sharing might make sense if you rarely need care.
- Do you want an out-of-pocket cap? Plans K and L have annual out-of-pocket limits (unlike A, B, G, N), which can be reassuring if you want maximum predictability.
When Can You Buy a Medigap Plan?
The best time to buy a Medigap plan is during your Medigap Open Enrollment Period — the 6-month window that starts the month you turn 65 and are enrolled in Medicare Part B. During this period:
- Insurance companies cannot deny you coverage or charge you more due to pre-existing conditions
- You have access to any plan available in your area
- You can switch plans later, but you may face medical underwriting
Outside of open enrollment, you may still be able to buy a Medigap plan, but insurers can charge higher premiums or deny coverage based on your health. Some states have additional protections — check with your state’s insurance department.
Can You Have Both Medicare Advantage and Medigap?
No. You cannot have both a Medicare Advantage plan and a Medigap policy at the same time. You must choose one:
- Original Medicare + Medigap: You have more freedom to see any Medicare provider; Medigap covers your gaps
- Medicare Advantage: An all-in-one alternative with network restrictions but often lower overall costs
If you have Medicare Advantage and want to switch to Original Medicare + Medigap, you can do so during certain enrollment periods.
Key Takeaways
- Most Medigap plans — A, B, D, G, and N — cover the Part B 20% coinsurance in full.
- Plan G is the most popular comprehensive plan for new beneficiaries, covering everything except the Part B deductible.
- Plan N is a budget-friendly option with the same 20% coverage but some office visit copays.
- Plans C and F (most comprehensive) are no longer available to beneficiaries who became eligible after January 1, 2020.
- Your best window to buy is during your Medigap Open Enrollment Period — don’t miss it.
- Premiums vary by age, location, and carrier — shop around before committing.
Bottom Line
Medigap plans are one of the most effective ways to protect yourself from the open-ended 20% Part B coinsurance that comes with Original Medicare. Plan G offers the most comprehensive coverage for most beneficiaries, while Plan N is a solid lower-premium alternative if you’re willing to absorb small copays for office and ER visits.
The most important thing you can do is enroll during your open enrollment window when you first become eligible — that’s when you have the most plan choices and the best rates, guaranteed.
Next step: Contact a licensed Medigap agent or use Medicare’s online plan comparison tool to get quotes for plans available in your area. Compare at least 3 carriers before making a decision—the same coverage can vary by hundreds of dollars per month.
