Medigap in 2025: How Medicare Supplement Insurance Works, Which Plan Fits You, and Why the Enrollment Window Changes Everything
Medigap is the most powerful tool available for closing the financial gaps in Original Medicare — but it is also one of the most misunderstood. Miss the enrollment window, and you may face medical underwriting for the rest of your life. Choose the wrong plan, and you may overpay for coverage you don't need, or underinsure yourself. This guide explains everything you need to make the right call.
The Problem Medigap Solves
Original Medicare is, in one sense, remarkably good coverage — the federal government bearing the cost of hospital stays, surgery, chemotherapy, dialysis, and thousands of other medical services. But it has a structural weakness that most beneficiaries only fully appreciate when they encounter it: there is no cap on what you can owe.
The 20% coinsurance that Part B requires after your deductible applies to every single service, without ceiling. A $200,000 course of chemotherapy generates $40,000 in out-of-pocket cost-sharing. A major orthopedic surgery at $100,000 generates $20,000 in coinsurance. Add in the Part A hospital deductibles — $1,676 per benefit period in 2025, potentially owed multiple times in a year — and the financial exposure from a serious illness under Original Medicare alone is severe.
Medigap — formally called Medicare Supplement Insurance — is the solution to this problem. It is insurance that covers the cost-sharing that Medicare leaves behind. Because Medigap plans pay after Medicare, and because Medicare's cost-sharing structure is completely standardized by federal law, every insurer offering the same lettered plan (Plan G, Plan N, etc.) must provide identical benefits. The only variable between insurers is the premium.
This is a consumer's dream — or should be. In practice, many beneficiaries overpay for Medigap because they buy the first policy they are shown rather than shopping multiple insurers. On an identical Plan G, premiums in the same ZIP code can vary by $100 or more per month between insurers.
The Standardized Plans: What A Through N Actually Cover
There are ten federally standardized Medigap plans, labeled A through N (with gaps — plans B, E, H, I, and J are no longer sold to new enrollees as of 2010). Each plan covers a defined set of benefits, and that set is identical from insurer to insurer. You may pay more or less for Plan G depending on which company you buy from, but the coverage — what gets paid when you have a claim — is exactly the same.
Two plans are now closed to new enrollees: Plan F (which covered the Part B deductible) and Plan C (which also covered the Part B deductible). Congress eliminated these plans for new enrollees as of January 1, 2020, because paying the Part B deductible for beneficiaries reduced their "skin in the game" and led to higher utilization. If you enrolled in Plan F or C before 2020, you may keep it.
For new enrollees, the three most relevant plans are Plan G, Plan N, and High-Deductible Plan G. Understanding what separates them is the central task of Medigap plan selection.
| Benefit | Plan G | Plan N | HD Plan G |
|---|---|---|---|
| Part A deductible ($1,676/period) | ✓ | ✓ | ✓ (after deductible) |
| Part A hospital coinsurance | ✓ | ✓ | ✓ (after deductible) |
| Part A hospice coinsurance | ✓ | ✓ | ✓ |
| Part B annual deductible ($257) | ✗ | ✗ | ✗ |
| Part B coinsurance (20%) | ✓ (100%) | ✓ (with $20 copay) | ✓ (after deductible) |
| Part B excess charges | ✓ | ✗ | ✓ (after deductible) |
| Skilled nursing coinsurance | ✓ | ✓ | ✓ (after deductible) |
| Foreign travel emergency (80%) | ✓ | ✓ | ✓ |
| Annual deductible | None | None | $2,870 (2025) |
| Typical monthly premium (age 65) | $140–$280 | $100–$200 | $35–$75 |
Premiums vary significantly by age, sex, tobacco use, and location. The figures above are illustrative; always get a personalized quote.
Plan G vs. Plan N: How to Actually Choose
The choice between Plan G and Plan N comes down to two variables: how often you see specialists, and whether you live in an area with a meaningful share of non-participating physicians (those who can charge Part B excess charges).
Plan N has copays: up to $20 for office visits and up to $50 for emergency room visits that do not result in inpatient admission. If you see your primary care physician four times a year and a specialist twice, that is $80–$160 in annual copays — well within the typical $30–$80/month premium savings Plan N offers compared to Plan G in the same market. For healthy seniors who rarely need care, Plan N is almost always the better financial choice.
Plan N's second vulnerability is excess charges. About 4% of physicians nationally opt out of Medicare assignment and can bill up to 15% above Medicare rates. In most markets, this is a minor risk. But in certain areas — parts of New York City, parts of New Jersey, pockets of South Florida — the non-participation rate is notably higher. If your preferred specialists do not accept assignment, Plan G's excess charge coverage becomes meaningful protection.
High-Deductible Plan G is worth serious consideration for healthy seniors who want catastrophic-level protection at a minimal premium. You pay a $2,870 deductible in 2025 before the plan kicks in — but premiums of $35–$75/month mean annual costs rarely exceed $1,800 in premiums alone, vs. $1,680–$3,360 for standard Plan G. If you stay healthy, HD Plan G wins on cost. If you have a major health event, the deductible is your maximum additional exposure before Plan G-level coverage activates.
The Guaranteed Issue Window: The Most Important 6 Months of Your Medicare Life
The Medigap Open Enrollment Period is a 6-month window that begins the first month you are simultaneously age 65 (or older) and enrolled in Medicare Part B. During this window, federal law requires every insurer licensed to sell Medigap in your state to offer you any plan they sell — at their standard age-rated premium — regardless of your health history.
This means a 65-year-old with diabetes, heart disease, and a recent cancer diagnosis pays the exact same premium for Plan G as a perfectly healthy 65-year-old of the same age, sex, and location from the same insurer. The insurer cannot ask about your health, cannot impose waiting periods for pre-existing conditions, and cannot deny your application.
After this window closes, most states allow insurers to use your health history. This is called "medical underwriting," and it can result in denial of coverage or substantially higher premiums. The stories from beneficiaries who missed their guaranteed issue window are among the most financially painful in Medicare planning — people with serious diagnoses who are now uninsurable for Medigap, or who pay $400–$600/month for a plan that a healthy peer pays $150/month for.
Do not miss this window. Even if you are not sure which plan you want, enrolling in a Medigap policy during the guaranteed issue window and later switching is generally more advantageous than waiting.
State-by-State: Where Medigap Rules Are Different
Massachusetts: The Gold Standard
Massachusetts operates an entirely different Medigap system. Rather than the federal A–N standardized plans, Massachusetts has three standardized plans: the Core plan, Supplement 1, and Supplement 1A. And crucially, Massachusetts offers guaranteed issue for Medigap year-round — any Medicare beneficiary enrolled in Part B can buy a Medigap plan at any time without health questions.
The Massachusetts Core plan covers basic hospitalization costs. Supplement 1 is the most in-depth option, covering coinsurance for hospital stays, skilled nursing, and foreign travel, but notably not the Medicare Part B coinsurance (the 20%). Supplement 1A adds Part B coinsurance coverage. Massachusetts residents have a significant advantage over most other states: the continuous open enrollment right means you can change plans at any time, giving you far more flexibility to respond to changing health needs or find better premiums.
Minnesota: Standardized to Different Plans
Minnesota also opted out of the federal standardized plan structure. It has its own standardized plans — Basic and Extended Basic — that differ somewhat from the federal plan letters. Like Massachusetts, Minnesota has historically offered some additional consumer protections around Medigap enrollment. Minnesotans should work with a local broker familiar with the state's specific plan structures.
Wisconsin: Another Independent System
Wisconsin rounds out the trio of states with independent Medigap standardization. Wisconsin's basic plan covers the essential Original Medicare cost-sharing items. Additional riders can be added for items like the Medicare Part A deductible or additional skilled nursing coverage. Wisconsin beneficiaries must understand that when reading national Medigap comparison articles, the plan letter descriptions do not map to Wisconsin's offerings.
New York and Connecticut: Guaranteed Issue Year-Round
New York and Connecticut both require Medigap insurers to offer guaranteed issue to Medicare beneficiaries year-round — similar to Massachusetts. This is a massive consumer protection. A New York beneficiary who was on Medicare Advantage for years and then develops a serious condition can switch back to Original Medicare and buy a comprehensive Medigap plan without being penalized for their health history. In most other states, that same beneficiary would face underwriting and likely be denied or rated up substantially.
States with Birthday Rules
California's birthday rule — the most well-known example — gives Medigap enrollees a 60-day window each year, starting on their birthday, to switch to any Medigap plan with equal or lesser benefits from any insurer, without medical underwriting. This allows California beneficiaries to price-shop annually and potentially move to a lower-cost insurer without health questions.
Similar birthday rules are now in effect in Idaho, Illinois, Louisiana, Maryland, Missouri, Nevada, Oklahoma, and Oregon, with variations in window length and eligible plan types. These provisions meaningfully weaken the lock-in effect of initial Medigap enrollment and give beneficiaries in these states considerably more long-term flexibility.
Florida, Texas, and Most Other States: Standard Rules Apply
In Florida, Texas, and the majority of states, the federal standard rules apply: a one-time 6-month open enrollment window at 65, limited guaranteed issue rights for specific life events, and medical underwriting thereafter. Florida's high concentration of seniors makes Medigap a major market — and the competition among insurers keeps Plan G premiums relatively competitive in the major metro areas. Texas's vast geography means premiums vary considerably from urban Dallas or Houston to rural west Texas.
Pricing Methodologies: Why Your Premium Grows Differently Depending on the Policy
All Medigap premiums are not priced the same way. There are three fundamental pricing approaches, and the one used by your insurer determines how your premium will grow over time — which matters enormously for long-term cost planning.
Community-rated plans charge the same premium to everyone who buys that plan in a given area, regardless of age. A 65-year-old and a 78-year-old pay the same rate. Premiums still increase over time, but they go up due to inflation and medical cost trends — not because of your age.
Issue-age-rated plans set your premium based on your age when you first buy the policy. A 65-year-old buying today pays less than a 70-year-old buying the same plan today. Your premium does not automatically increase as you age — but it does increase over time due to medical cost trends.
Attained-age-rated plans start low but increase as you age. These policies tend to have the lowest initial premiums — and the highest long-term costs. The premium you pay at 75 or 80 under an attained-age policy can be dramatically higher than what a same-age peer pays who bought a community-rated or issue-age-rated policy.
When comparing Medigap quotes, always ask the insurer or broker which pricing methodology is used. An attained-age Plan G at $120/month at age 65 may look cheaper than a community-rated Plan G at $150/month — but by age 75, the attained-age policy could cost $220–$280/month while the community-rated policy is at $180/month.
What People Get Wrong About Medigap
❌ Mistake #1: Missing the guaranteed issue window
This is the single costliest Medigap mistake. The 6-month window at 65 when you first enroll in Part B is your only federally guaranteed, no-questions-asked chance to buy Medigap in most states. After it closes, you may be underwritten — and if your health has changed, you may be denied or rated up for years.
❌ Mistake #2: Buying from the first insurer you're shown
Because Plan G is identical from every insurer, the only variable is premium and pricing methodology. Two companies offering Plan G in the same ZIP code can differ by $100+ per month for identical coverage. Always get quotes from at least 3–5 insurers. The National Association of Insurance Commissioners (NAIC) Medigap rate comparison tools and state insurance commissioner websites can help.
❌ Mistake #3: Not asking about rate increase history
Some insurers have a pattern of offering low initial premiums to attract new enrollees, then aggressively raising rates in subsequent years. Before buying, ask the broker or insurer for 5-year historical rate increase data. An insurer with steady 3–5% annual increases is preferable to one that stays flat for two years and then jumps 15%.
❌ Mistake #4: Thinking Medigap covers everything
Even comprehensive Plan G leaves gaps: the Part B deductible ($257/year), prescription drugs, dental, vision, and hearing. You still need a Part D drug plan. And if you want dental or vision coverage, you need separate policies. Medigap is not all-inclusive insurance — it is a supplement to Original Medicare's specific cost-sharing.
❌ Mistake #5: Confusing Medigap with Medicare Advantage
Medigap and Medicare Advantage are incompatible — you cannot have both. Medigap works with Original Medicare. Medicare Advantage replaces Original Medicare. This distinction seems obvious once stated, but it confuses many new Medicare enrollees, particularly those who are approached by agents selling both types of coverage.
Frequently Asked Questions
What is the difference between Medigap and Medicare Advantage?+
Medigap (also called Medicare Supplement Insurance) works alongside Original Medicare — it pays the cost-sharing amounts (deductibles, coinsurance, copays) that Original Medicare does not cover. You keep Original Medicare and use any doctor or hospital that accepts Medicare, nationwide. Medigap does not replace Medicare; it supplements it. Medicare Advantage, by contrast, replaces Original Medicare with a private plan that has its own network, cost-sharing rules, and benefit structure. You cannot have both Medigap and Medicare Advantage at the same time.
What does Medigap Plan G cover in 2025?+
Medigap Plan G covers: the Part A hospital deductible ($1,676 in 2025), all Part A coinsurance and hospital costs through 365 additional days after Medicare benefits are exhausted, Part A hospice care coinsurance, Part B coinsurance and copayments (the 20% that Medicare does not pay), skilled nursing facility coinsurance (days 21–100), Part B excess charges (when doctors charge above Medicare rates), and 80% of foreign travel emergency care costs (up to a $50,000 lifetime maximum after a $250 deductible). Plan G does NOT cover the Part B annual deductible ($257 in 2025) — that is the only gap. Everything else is covered.
What is Medigap guaranteed issue and when does it apply?+
Guaranteed issue means an insurer must sell you a Medigap policy without asking health questions and without charging higher premiums based on your health history. Your primary guaranteed issue right is the Medigap Open Enrollment Period: the 6-month window that begins the first month you are both 65 or older AND enrolled in Medicare Part B. During this window, any insurer licensed to sell Medigap in your state must sell you any plan they offer. After this window closes, most states allow medical underwriting — insurers can deny your application or charge higher premiums based on health. There are also limited guaranteed issue rights when you lose other coverage (employer plan ending, Medicare Advantage plan leaving your area, etc.).
Why is Massachusetts different for Medigap?+
Massachusetts does not use the standardized federal Medigap plan letters (A through N). Instead, it has its own standardized plans: the Core plan, Supplement 1, and Supplement 1A. More significantly, Massachusetts offers guaranteed issue for Medigap year-round — not just during the initial open enrollment window. Any Massachusetts resident who is enrolled in Original Medicare may purchase a Medigap plan at any time without medical underwriting. This provides a level of access and flexibility unavailable in most other states, and makes Original Medicare + Medigap a particularly attractive option for Massachusetts residents.
What is the birthday rule for Medigap, and which states have it?+
Some states have enacted "birthday rules" that give Medigap enrollees an annual window — typically 30–60 days around their birthday — to switch to a different Medigap plan with equal or lesser benefits without medical underwriting. As of 2025, states with some form of birthday rule or annual open enrollment right include: California, Idaho, Illinois, Louisiana, Maryland, Missouri, Nevada, Oklahoma, and Oregon. Rules vary by state in terms of window length and which plans are covered by the rule. These provisions give Medigap enrollees in these states meaningful ability to shop for better rates annually — an important protection given that Medigap premiums tend to increase with age.
Can I be denied Medigap coverage because of pre-existing conditions?+
Outside of your guaranteed issue rights, yes — in most states. During medical underwriting, insurers can ask about your health history and may deny your application or charge higher premiums if you have pre-existing conditions. Common conditions that can trigger higher rates or denial include: heart disease, diabetes, COPD, cancer history, kidney disease, and stroke history. This is why enrolling during your 6-month guaranteed issue window is so important — it is your only time to buy Medigap based solely on your age and the plan you choose, not your health. Exceptions: New York, Connecticut, Massachusetts, Maine, and Vermont all offer some form of year-round or extended guaranteed issue rights.
Does Medigap cover prescription drugs?+
No. Medigap plans sold since 2006 do not include prescription drug coverage. If you have Original Medicare with a Medigap plan, you need a separate Medicare Part D prescription drug plan to cover your medications. Part D plans are sold by private insurers and vary widely in premiums, formularies, and cost-sharing. The standard Part D premium in 2025 averages around $40–$50/month, though low-income beneficiaries may qualify for Extra Help (Low Income Subsidy) that reduces or eliminates Part D costs.
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