Medicare Supplement

Medigap Plan Letters Explained: A Plain-English Guide

MOUNT PLEASANT, S.C. — If you've ever tried to make sense of Medicare Supplement Insurance, you've probably run into a wall of letters: Plan A, Plan G, Plan N, Plan K. It looks like alphabet soup. The good news? Those letters follow a set of rules, and once you understand the pattern, the choices get a lot less confusing.

Here's a plain-English look at what Medigap does, how the standardized letters work, and the common mistakes to sidestep along the way.

What Medigap actually does

Medicare Supplement Insurance — often called Medigap — is private insurance that helps pay some of the costs Original Medicare (Part A and Part B) leaves behind. That includes things like coinsurance, copayments, and deductibles.

A Medigap policy works alongside Original Medicare, not instead of it. Medicare pays its share first, and your Medigap policy picks up some or all of what's left, depending on the letter you chose.

A few things Medigap does not do:

• It does not cover prescription drugs. For that, you'd add a separate Part D plan.
• It does not work with Medicare Advantage. You have Medigap or you have Medicare Advantage — not both.
• It generally does not cover dental, vision, hearing aids, or long-term care.

Why the letters exist

Before the early 1990s, Medigap policies were a mess. Every company sold something different, and comparing them was nearly impossible. Congress stepped in and required most Medigap plans to be standardized into lettered categories.

Today, in most states (including South Carolina), Medigap policies come in 10 standardized letter plans: A, B, C, D, F, G, K, L, M, and N. Massachusetts, Minnesota, and Wisconsin have their own systems.

Here's the key idea: the benefits inside each letter are set by law. A Plan G sold by Company X covers the exact same Medicare gaps as a Plan G sold by Company Y. The only differences are the price, the customer service, and how the company handles rate increases over time.

What each letter covers (in broad strokes)

Every Medigap plan covers at least these basics:

• Part A hospital coinsurance, plus up to 365 extra hospital days after Medicare runs out
• Part B coinsurance or copayment (some plans cover a share, others cover it in full)
• The first three pints of blood each year
• Part A hospice care coinsurance

From there, the letters differ in how much of the remaining gaps they fill — things like the Part A deductible, skilled nursing coinsurance, and foreign travel emergency care.

Two quick notes worth knowing:

• Plans C and F are only available to people who became eligible for Medicare before Jan. 1, 2020. If you turned 65 after that date, those two letters are off the table.
• Plans K and L have out-of-pocket limits but pay a smaller share of certain costs until you hit that limit.

For a side-by-side benefits chart, Medicare's official comparison tool at medicare.gov is the best place to look.

How Medigap fits with the rest of Medicare

If you have Original Medicare and want help with the gaps, your choices generally look like this:

• Original Medicare + Medigap + a Part D drug plan. This route uses three pieces working together.
• Medicare Advantage (Part C). A single private plan that bundles Part A, Part B, and usually Part D. You cannot pair this with Medigap.

Mount Pleasant is in Charleston County, where residents have access to both Medicare Advantage plans and stand-alone Part D drug plans through the federal Medicare marketplace. Medigap, on the other hand, is sold year-round by private insurers and is not tied to the same annual windows as Advantage and Part D.

Speaking of those windows: the Annual Enrollment Period runs Oct. 15 through Dec. 7, and the Medicare Advantage Open Enrollment Period runs Jan. 1 through March 31. Those dates matter for Advantage and Part D — not for buying Medigap.

The one enrollment window that really matters for Medigap

Here's the mistake that costs people the most: missing the Medigap Open Enrollment Period.

This is a six-month window that starts the month you're 65 or older AND enrolled in Part B. During that window, insurers must sell you any Medigap policy they offer at their best available rate, regardless of your health history.

Outside that window, insurers in most states can use medical underwriting — meaning they can charge you more, or turn you down entirely, based on your health. There are some limited protections called "guaranteed issue rights," but they don't cover every situation.

If you're approaching 65, or just signing up for Part B, this is not a deadline to sleep on.

A few 2026 numbers worth knowing

Even if you're focused on Medigap, these program-level figures affect the bigger Medicare picture:

• Part D out-of-pocket cap: $2,100 for 2026. Once you hit that in covered drug costs, you're done paying for the year.
• Part D maximum deductible: $615.
• The coverage gap ("donut hole") is gone as of 2025. Part D now has three phases.
• The Medicare Prescription Payment Plan lets you spread drug costs across the year in monthly installments if that helps your budget.
• IRMAA surcharges — the higher-income adjustments to Part B and Part D — begin above $109,000 for a single filer in 2026.