Medigap, also called Medicare Supplement Insurance, is private health insurance designed to work alongside Original Medicare Parts A and B by covering some or all of the cost-sharing that Medicare leaves in your hands. The deductibles, coinsurance, and copays that Original Medicare doesn’t pay, the gaps it leaves open, are exactly what Medigap is named for. A well-chosen Medigap plan can convert Original Medicare from a program with potentially unlimited annual out-of-pocket exposure into one with highly predictable, manageable costs. That predictability is something a lot of people don’t fully appreciate until they’re staring at an unexpected hospital bill.
Medigap is only available to people enrolled in Original Medicare Parts A and B. You can’t have a Medigap plan alongside Medicare Advantage, because Medicare Advantage replaces Original Medicare rather than supplementing it. If you want the security of knowing your cost-sharing is capped and covered, you’ve got two structural paths: Original Medicare plus a Medigap plan, or Medicare Advantage, which provides its own annual out-of-pocket maximum.
How Medigap Plans Are Standardized
Federal law standardizes Medigap plan designs. Every Medigap plan of the same letter (Plan G, Plan N, Plan F, and so on) offers exactly the same benefits regardless of which private insurance company sells it. A Plan G from Blue Cross Blue Shield and a Plan G from Humana cover exactly the same things. The only difference between plans of the same letter from different companies is the monthly premium. This standardization makes Medigap comparison shopping unusually straightforward compared to almost every other insurance decision: once you know which letter plan suits your needs, you simply compare premiums for that plan across all companies operating in your state.
The standardized plan letters available vary slightly by state, but in most states the available plans are A, B, D, G, K, L, M, and N. Plans C and F, which were the most comprehensive options, are no longer available to people who became Medicare-eligible on or after January 1, 2020. If you became eligible before 2020 and enrolled in Plan C or F, you can keep it, but you can’t buy those plans fresh anymore. For people new to Medicare, Plan G is now the most comprehensive Medigap option available, and it’s the plan most brokers and SHIP counselors start the conversation with.
What Plan G Covers: The Full Breakdown
Plan G is the most comprehensive Medigap plan available to new Medicare enrollees. It covers the Part A deductible, which is $1,676 per benefit period in 2025. It covers Part A hospital cost-sharing for days 61 through 90 and the lifetime reserve days. It covers Part A skilled nursing facility coinsurance for days 21 through 100. It covers the Part B coinsurance, which is the 20% of Medicare-approved costs you’d otherwise pay after your Part B deductible. It covers Part B excess charges, the up-to-15% above the Medicare-approved rate that non-participating providers can charge. And it covers foreign travel emergency care up to plan limits.
The only gap Plan G doesn’t cover is the annual Part B deductible, which is $257 in 2025. You pay that once per year, and after that, Plan G covers the remaining standard cost-sharing for covered services for the rest of the calendar year. In practical terms, a Plan G enrollee’s maximum predictable out-of-pocket for covered services from participating providers after the deductible is effectively zero. You pay a known premium each month, the Part B deductible once a year, and virtually nothing else when you need care. That’s the value proposition in plain terms.
High-Deductible Plan G is a variation worth knowing about. It comes with a lower monthly premium but requires you to pay a deductible, $2,870 in 2025, before the Medigap benefits kick in. It’s conceptually similar to a high-deductible health plan in the under-65 market: lower monthly cost, higher initial exposure, meaningful protection if something serious happens. High-Deductible Plan G makes sense for people who are relatively healthy, want to reduce their monthly premium, and are comfortable handling a few thousand dollars in potential out-of-pocket before their Medigap coverage activates. You’re essentially self-insuring the deductible in exchange for lower premiums year over year.
Plan N: The Lower-Premium Alternative
Plan N is a popular alternative to Plan G that trades some cost-sharing coverage for a meaningfully lower monthly premium. Plan N covers the same Part A benefits as Plan G and also covers Part B coinsurance, but with two exceptions. First, you pay copays for office visits: up to $20 for primary care and specialist visits. Second, you pay up to $50 for emergency room visits that don’t result in an inpatient hospital admission. Plan N also doesn’t cover Part B excess charges, which means if you see a provider who doesn’t accept Medicare assignment, you’re responsible for the up-to-15% balance they can bill above the Medicare-approved amount.
Plan N premiums are typically $40 to $80 per month less than Plan G premiums for the same age and gender in most markets. Over a year that’s $480 to $960 in premium savings. Whether those savings justify the office visit copays and the absence of excess charge coverage depends on how you actually use healthcare. If you visit the doctor frequently, the copays eat into your savings quickly. If you can limit yourself to Medicare-participating providers (and most providers do accept Medicare assignment), the excess charge exposure is minimal. If you’re relatively healthy and see the doctor a handful of times a year, Plan N’s premium savings often come out ahead.
Running the math for your specific situation helps. Take your premium difference between Plan G and Plan N. Add up your expected office visit copays for the year. If the copays plus any excess charge exposure you might face is less than the premium difference, Plan N wins financially. Most people who do this comparison find Plan N is the better deal in their 60s and 70s when they’re relatively healthy, though some switch to Plan G later when healthcare utilization increases. The good news is you’re not locked in forever: you can apply to switch between plans at any time, though outside your guaranteed issue window, that switch is subject to medical underwriting.
Medigap Pricing: How Premiums Are Set
Medigap insurers use three different pricing methodologies, and which one your plan uses significantly affects how your premium grows over time. Community-rated plans charge the same premium to all enrollees regardless of age, so a 65-year-old and a 78-year-old pay the same rate for the same plan from the same company. Issue-age-rated plans set premiums based on your age when you first enroll, meaning your rate is locked to your entry age and doesn’t increase just because you get older (though it can increase for inflation and claims experience). Attained-age-rated plans set premiums based on your current age and increase every year as you get older.
Attained-age-rated plans are often the cheapest option at age 65, which makes them look very attractive in the initial comparison. But they become increasingly expensive as you age, and they often surpass community-rated or issue-age-rated plan premiums for people in their 70s and 80s. Most people keep their Medigap plans for 10, 20, even 30 years. Over that time horizon, a plan that starts cheap and grows 5% to 7% annually due to age plus inflation can become significantly more expensive than a plan that started slightly higher but doesn’t have the annual age-based increase layered in. If you’re comparing Medigap plans at 65, ask which pricing method each company uses. It matters more than the starting premium difference.
When to Buy Medigap: The Guaranteed Issue Period
The most important thing to know about Medigap enrollment timing is the Medigap Open Enrollment Period. This is the 6-month window that begins on the first day of the month in which you’re both 65 or older and enrolled in Medicare Part B. During this window, any insurance company selling Medigap in your state must sell you any plan they offer without medical underwriting. They can’t deny you coverage, charge you more based on your health history, or impose waiting periods for pre-existing conditions. You’re in, at standard rates, period.
Outside your Medigap Open Enrollment Period, insurance companies in most states can apply full medical underwriting. They can charge you significantly more based on your health conditions, or decline to sell you a policy at all. This isn’t a minor inconvenience. Someone with diabetes, heart disease, cancer history, or even sleep apnea can be turned down entirely in states without additional protections. A few states (notably New York, Massachusetts, and Connecticut) have stronger guaranteed issue rules that protect Medigap access year-round. But in most states, if you miss your initial 6-month window without a qualifying event that restores guaranteed issue rights, your Medigap options can be severely limited for the rest of your life.
Most people skip this part and regret it. They figure they’ll buy Medigap later once they see how Medicare works, or they join a Medicare Advantage plan because it’s cheaper upfront and assume they can switch to Medigap whenever they want. Switching from Medicare Advantage back to Original Medicare with a Medigap plan is often possible coverage-wise, but in most states it requires passing medical underwriting to get the Medigap policy. If your health has changed since you were 65, you may find yourself unable to get Medigap at any price. That’s the trap a lot of people don’t see coming.
When Guaranteed Issue Rights Are Restored
Guaranteed issue rights for Medigap can be restored in specific circumstances. If you enrolled in a Medicare Advantage plan for the first time and you disenroll within your first 12 months and return to Original Medicare, you have a guaranteed right to buy certain Medigap plans without medical underwriting. This is sometimes called the “trial right” for Medicare Advantage. It’s designed to protect people who try Medicare Advantage and decide it’s not right for them.
Other guaranteed issue triggers include: your Medigap insurer goes bankrupt or leaves the market and you lose your coverage through no fault of your own, you move out of your Medicare Advantage plan’s service area, or your Medicare Advantage plan terminates. These are narrow exceptions. They don’t cover cases where you simply decided to drop your Medigap coverage voluntarily and then changed your mind later. The safest approach by far is to make your Medigap decision during your initial guaranteed issue window, before your health situation changes and before you’ve lost the leverage that guaranteed issue gives you.
Medigap vs. Medicare Advantage: The Core Trade-Off
Original Medicare plus Medigap offers nationwide provider access with no network restrictions, predictable out-of-pocket costs after your premium and Part B deductible, freedom from prior authorization for most services, and the ability to see any Medicare-participating specialist anywhere in the country. If you travel frequently, have a complex medical situation requiring specialists at top academic medical centers, or simply want the freedom to see whoever you want without referrals or prior approvals, this combination is hard to beat. The trade-off is higher combined monthly cost. Part B premium plus Medigap premium plus a standalone Part D premium can total $400 to $600 or more per month depending on plan choice, age, and where you live.
Medicare Advantage typically offers lower monthly premiums, often bundled drug coverage, and extra benefits like dental, vision, and hearing that Medigap doesn’t include. The trade-off is network restrictions, prior authorization requirements that can delay or complicate care for certain services, and potential for higher cost-sharing if you need significant care within the plan’s structure. Neither approach is universally better. The right answer depends on your health situation, provider relationships, how much you value geographic flexibility, your financial situation, and your personal tolerance for insurance complexity versus premium cost. What’s certain is that making this decision without fully understanding both options, and without understanding the Medigap guaranteed issue timing, is the most common and costly Medicare mistake people make.
Finding and Comparing Medigap Plans
Once you’ve decided Medigap is the right structure for you, the comparison is relatively simple. Because all Plan G policies offer the same benefits, you’re comparing premiums and company financial stability. Medicare.gov has a Medigap policy search tool that shows all insurers offering each plan type in your zip code. Your state’s insurance department website often has similar tools. Your SHIP (State Health Insurance Assistance Program) counselor can help you compare options for free, without any sales pressure, and they often know which local insurers have the most stable long-term premium history in your area.
Don’t just buy from the company with the lowest current premium without asking about their pricing methodology and their historical rate increase patterns. A company that’s consistently raised premiums 8% to 10% per year is a different long-term bet than one that’s raised them 3% to 4%. Ask insurers directly for their rate increase history for your specific plan in your state over the past 5 years. Most companies will provide this. It’s one of the most useful data points you can get when making a decision you’ll likely live with for the next 20 or 30 years.