“Medicare gap” refers to the out-of-pocket costs that Original Medicare (Parts A and B) doesn’t fully cover. These gaps include deductibles, copayments, and coinsurance that you’re responsible for, plus entire categories of care like dental, vision, and hearing that Medicare simply doesn’t pay for at all. The term also sometimes refers to a specific stage in Part D prescription drug coverage where you historically paid more for medications, though recent legislation has significantly changed how that works.
Understanding where these gaps are helps you decide whether you need supplemental coverage and what kind makes the most sense for your situation.
Where Original Medicare Falls Short
Original Medicare covers a wide range of medical services, but it leaves you exposed in two important ways: cost sharing and coverage exclusions.
On the cost-sharing side, Part A (hospital insurance) comes with a deductible each time you’re admitted, and Part B (medical insurance) requires you to pay 20% of the approved amount for most outpatient services. That 20% has no cap. If you need an expensive surgery or ongoing treatment, your share of the bill can climb quickly. Unlike most private insurance plans, Original Medicare has no yearly limit on what you pay out of pocket.
Then there are the services Medicare doesn’t cover at all. These include:
- Routine dental care: cleanings, fillings, extractions, and dentures
- Eye exams for prescription glasses
- Hearing aids and fitting exams
- Long-term care in a nursing home or assisted living facility
- Routine physical exams (though Medicare does cover an annual wellness visit, which is different)
Medicare will cover some dental services when they’re directly tied to another covered procedure, such as dental work needed before a heart valve replacement, organ transplant, or certain cancer treatments. But for everyday dental needs, you’re on your own unless you have separate coverage.
Medigap: Supplemental Insurance for Cost Sharing
Medigap (officially called Medicare Supplement Insurance) is private insurance designed specifically to fill the cost-sharing gaps in Original Medicare. These plans help pay for the deductibles, copayments, and coinsurance that Medicare leaves behind. They don’t cover the excluded services like dental or vision, but they can dramatically reduce your out-of-pocket spending on the services Medicare does cover.
Medigap plans are standardized by the federal government and labeled with letters: Plan A, Plan B, Plan G, Plan K, Plan N, and so on. Each letter offers a specific set of benefits that’s the same regardless of which insurance company sells it. The difference between companies is price and customer service, not what’s covered.
Plan G is currently the most popular and comprehensive option available to new enrollees. It covers nearly all cost-sharing gaps, including the Part A deductible, the 20% Part B coinsurance, and excess charges from providers who don’t accept Medicare’s approved amount. The one thing Plan G doesn’t cover is the annual Part B deductible, which you pay once per year.
Plan F used to be the gold standard because it covered everything, including the Part B deductible. However, Plan F is no longer available to anyone who became eligible for Medicare on or after January 1, 2020. If you had Medicare before that date and already enrolled in Plan F, you can keep it. Everyone else is typically directed to Plan G or Plan N.
What Medigap Plans Cost
Monthly premiums vary based on the plan letter, your location, your age, and the insurance company. According to Kaiser Family Foundation data from 2023, the average monthly premium across all Medigap policyholders was $217. But that average masks a wide range.
Plan G averaged $164 per month nationally, ranging from around $140 in some states to $236 in New York. Plan F, which is only available to people who had Medicare before 2020, averaged $274 per month. More affordable options exist too: Plan N averaged $168 per month, while Plan K, which covers a smaller share of costs, averaged just $92.
These premiums typically increase as you age, and pricing methods vary by insurer. Some companies set rates based on your age when you first buy the policy (called “issue-age” pricing), while others adjust annually based on your current age (“attained-age” pricing). The pricing method can make a significant difference over time.
When to Enroll in Medigap
Timing matters more with Medigap than almost any other Medicare decision. Under federal law, you get a six-month Medigap Open Enrollment Period that starts the first month you have Part B and are 65 or older. During this window, insurance companies cannot refuse to sell you any Medigap policy they offer, cannot use medical underwriting to evaluate your application, and cannot charge you more because of pre-existing health conditions.
Once that six-month window closes, the protections largely disappear. Insurance companies can review your health history, deny your application, or charge higher premiums based on medical conditions. In some states, additional protections exist, but the federal guarantee is limited to that initial enrollment period. If you’re considering Medigap, enrolling during this window is significantly easier and often cheaper than trying to get coverage later.
The Part D Prescription Drug Gap
The other common meaning of “Medicare gap” is the coverage gap in Part D prescription drug plans, historically known as the “donut hole.” This was a stage of drug spending where you paid a much larger share of your medication costs after exceeding an initial coverage limit but before reaching catastrophic coverage.
The Inflation Reduction Act changed this significantly. Starting in 2025, Medicare Part D now has a $2,000 annual out-of-pocket cap on prescription drug spending. Once you hit that limit, you pay nothing more for covered medications for the rest of the year. This effectively eliminates the old donut hole structure that left many people with high drug costs in the middle of the year.
It’s worth noting that while the out-of-pocket cap helps people with high drug costs, some plan designs have shifted in response. Research published in 2025 found that as the Inflation Reduction Act’s changes took effect, some Part D plans adjusted their cost-sharing structures in ways that may increase costs for beneficiaries who don’t reach the $2,000 cap, particularly those in Medicare Advantage plans.
Medigap vs. Medicare Advantage
Medigap isn’t the only way to address coverage gaps. Medicare Advantage (Part C) is an alternative approach where private insurers bundle hospital, medical, and often prescription drug coverage into a single plan. Many Medicare Advantage plans also include dental, vision, and hearing benefits that Original Medicare lacks.
The key structural difference: Medicare Advantage plans are required to set a yearly out-of-pocket maximum. Once you hit that limit, covered services cost you nothing for the rest of the year. Original Medicare has no such limit unless you add Medigap or other supplemental coverage.
The tradeoff is that Medicare Advantage plans typically use provider networks, meaning you may need referrals and could pay more for out-of-network care. Medigap paired with Original Medicare lets you see any provider who accepts Medicare, anywhere in the country, with no network restrictions. You generally can’t have both Medigap and Medicare Advantage at the same time. Choosing between them depends on how you prioritize flexibility, cost predictability, and extra benefits like dental coverage.