Medicare Supplement

Medigap, explained: what Plans A–N actually cover

EUREKA, Calif. — If Original Medicare feels like it leaves too many blanks on the bill, you're not imagining it. Parts A and B pay for a lot, but they don't cap what you can owe out of pocket. That's the gap Medicare Supplement insurance — better known as Medigap — is designed to help fill, and the plans come in standardized letters so you can compare them side by side.

What Medigap actually does

Medigap is private insurance that sits on top of Original Medicare. After Medicare pays its share of a covered service, your Medigap plan picks up some or all of what's left — things like the Part A hospital coinsurance, the Part B 20% coinsurance, and extra hospital days after Medicare's benefits run out.

It does not replace Medicare. You still need Part A and Part B, and Medicare still pays first. Medigap simply helps with the leftover costs that Original Medicare doesn't cap.

One important limit: Medigap plans sold today do not include prescription drug coverage. For that, most people add a stand-alone Part D plan.

How the standardized letters work

To make shopping easier, the federal government requires Medigap plans to follow standard designs, each named with a letter. In most states, those letters are A, B, C, D, F, G, K, L, M, and N. (Massachusetts, Minnesota, and Wisconsin have their own standardized systems.)

Here's what "standardized" means in plain English: Plan G from one company covers the exact same list of benefits as Plan G from another company. The price and customer service can differ, but the benefits inside each letter are identical by law.

A few letters worth knowing:

• Plan G is a popular choice for newer enrollees because it covers most gaps after you pay the annual Part B deductible.
• Plan N usually has lower premiums but asks you to pay small copays for some office and emergency visits.
• Plans K and L have lower premiums in exchange for cost-sharing and a yearly out-of-pocket limit.
• Plans C and F are only available to people who became eligible for Medicare before January 1, 2020.

You can compare the full benefit chart on medicare.gov.

When to buy — the window that matters most

The single most important date in Medigap isn't a national deadline like Oct. 15 or Dec. 7. It's personal: your 6-month Medigap Open Enrollment Period, which starts the month you're 65 or older and enrolled in Medicare Part B.

During that window, insurance companies must sell you any Medigap policy they offer at their best available rate, regardless of your health history. Miss it, and in most states insurers can use medical underwriting — which means they can charge you more or turn you down based on pre-existing conditions.

California residents, including folks here in Eureka, also have a state "birthday rule" that gives Medigap holders a yearly chance to switch to an equal or lesser plan without medical underwriting. Your local SHIP counselor (called HICAP in California) can walk you through the details.

Medigap vs. Medicare Advantage

Medigap and Medicare Advantage (Part C) are two different roads — you pick one or the other, not both.

• Medigap works with Original Medicare and lets you see any provider in the U.S. that accepts Medicare. You typically add a separate Part D plan for drugs.
• Medicare Advantage replaces the way you get your Part A and B benefits, usually through an HMO or PPO network, and often bundles in drug coverage and extras.

Eureka is in Humboldt County, where Medicare Advantage plan availability is set at the county level. If you're weighing the two paths, the number and type of Advantage plans in your county is one thing to check — but Medigap availability is regulated separately by the state and by each insurer.

What Medigap doesn't cover

Even the most generous Medigap plan has limits. Medigap generally does not pay for:

• Prescription drugs (that's Part D)
• Routine dental, vision, or hearing care
• Long-term custodial care in a nursing home
• Hearing aids or eyeglasses

If those benefits matter to you, you'll need to plan for them separately.

A note on 2026 drug costs

Medigap doesn't touch your drug plan, but two 2026 Part D figures are worth keeping in mind while you shop: the annual out-of-pocket cap on covered drugs is $2,100, and the maximum Part D deductible is $615. The old coverage gap ("donut hole") was eliminated in 2025, so Part D now has three phases. You can also opt into the Medicare Prescription Payment Plan to spread drug costs across the calendar year in monthly installments.

Higher-income enrollees may pay IRMAA surcharges on Part B and Part D; those start above $109,000 in income for a single filer in 2026.