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Medicare Supplement

Medigap letter plans explained for Columbia Medicare readers

COLUMBIA, Mo. — If you've been reading up on Medicare, you've probably seen a puzzling alphabet: Plan A, Plan G, Plan N, Plan K. These letters refer to Medicare Supplement Insurance, often called Medigap — and understanding how they work can take a lot of the guesswork out of choosing coverage.

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Key takeaways

  • Medigap plans are standardized, so a plan with a given letter, like Plan G, offers the same benefits no matter which insurance company sells it, though prices and service can differ.
  • There are 10 standardized Medigap plans (A, B, C, D, F, G, K, L, M, and N), but Plans C and F are only open to people who became eligible for Medicare before January 1, 2020.
  • The best time to buy a Medigap policy is during your six-month Medigap Open Enrollment Period, which starts the month you turn 65 or older and enroll in Part B, since insurers can't deny you or charge more for health reasons during that window.
  • You can have Medigap or Medicare Advantage, but not both, and it's not legal for someone to sell you a Medigap policy if they know you're already enrolled in Medicare Advantage.

Here's a plain-English look at what Medigap does, how the standardized letters work, and where Columbia residents can get help sorting it out.

What Medigap Actually Does

Medigap is private insurance that works alongside Original Medicare (Part A and Part B). It doesn't replace Medicare — it helps pay some of the out-of-pocket costs Original Medicare leaves behind, like coinsurance, copays, and sometimes deductibles.

A few key things to know:

Why the Letters Exist

Here's the part that trips up a lot of people: in most states, including Missouri, Medigap plans are standardized by the federal government. That means a Plan G is a Plan G, no matter which company sells it. The benefits are identical from carrier to carrier.

What can differ is the price, the company's customer service, and how they handle rate increases over time. But the coverage inside each lettered plan is set by rules, not by the insurer.

According to Medicare.gov, there are currently 10 standardized Medigap plans, identified by letters: A, B, C, D, F, G, K, L, M, and N. (Plans C and F are only available to people who became eligible for Medicare before January 1, 2020.)

How the Letters Compare

Rather than list every benefit, here's the shortcut for understanding the letters:

You can see the full benefits grid on Medicare.gov — it's the clearest side-by-side comparison available.

When You Can Buy One (This Matters)

The best time to buy a Medigap policy is during your Medigap Open Enrollment Period — a six-month window that starts the month you're 65 or older and enrolled in Part B. During this window, insurers can't turn you down or charge you more because of your health.

Outside that window, in most cases, insurers in Missouri can use medical underwriting, which means they can ask about your health and either decline you or raise your rate. This is one of the most important things to know before delaying a decision.

Deciding in Columbia and Boone County

Columbia is in Boone County, and Missouri residents have access to a range of Medigap carriers. Because the plan benefits are standardized, the smart approach is:

1. Pick the letter first based on how you want to handle out-of-pocket costs. 2. Then compare prices from multiple carriers offering that same letter. 3. Ask about rate history — how often has the company raised premiums?

Remember, Medigap is a separate decision from Medicare Advantage (Part C). You can have one or the other, not both. If you're already leaning toward Original Medicare because you want broad provider access and predictable coverage, Medigap is the companion piece that fills in the gaps.

Quick FAQ

Do I need a Medigap plan if I have Medicare Advantage? No — and in fact, it's not legal for someone to sell you a Medigap policy if they know you're on a Medicare Advantage plan. The two products don't work together.

Does Medigap cover my prescriptions? Generally no. You'd sign up for a separate Part D drug plan. For 2026, Part D has a $2,100 annual out-of-pocket cap and a maximum deductible of $615.

Can I switch Medigap plans later? You can apply anytime, but outside your initial six-month open enrollment window, insurers in Missouri can usually require medical underwriting. Some limited "guaranteed issue" rights apply in specific situations — worth asking about.

Is one letter better than another? There's no universal "best" letter — it depends on your budget, health, and how you feel about paying up front versus paying premiums. The right answer is personal.

Where to Get Unbiased Help

For personalized guidance in Columbia, these are the trustworthy places to start:

Take your time, ask questions, and remember that once you understand what the letters mean, the choice gets a lot less intimidating.

By the numbers

Medicare Part B premium, 2006–2026

The standard monthly Part B premium has climbed from $88.50 in 2006 to $202.90 in 2026. Hover any point for that year’s premium.

$0$50$100$150$200200820122016202020242026

Source: CMS. Standard premium shown; in some hold-harmless years many existing enrollees paid less. Confirm at Medicare.gov.

By the numbers

How people get Medicare in Boone County

49% are on Medicare Advantage
(MA penetration in Boone County)
49%
51%
Medicare Advantage Medicare Supplement (Medigap) Original Medicare only
U.S. average

MA penetration from CMS enrollment data; Medigap share is an estimate. U.S. average is about 54% Medicare Advantage. These are area-level figures, not plan-specific.

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Medicare Advantage companies in Boone County

By local enrollment size · informational, not a ranking
CompanyLocal enrollmentPlans offeredLocal agentsAction
UnitedHealthcareNational—Yes
HumanaNational—Yes
Aetna (CVS Health)National—Yes
Lumeris Group Holdings CorporationRegional—Yes
Centene (WellCare)National—Yes
Elevance Health (Anthem)National—Yes
Enrollment data: CMS Medicare Advantage enrollment by company (county level). Figures shown are illustrative sample data pending the current CMS file. Listed by enrollment size, largest first — this is not a ranking, recommendation, or endorsement of any company or plan.

Provided by licensed insurance partners; MyMedicarePlans.org may be compensated. Not a ranking or endorsement of any plan.

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The parts of Medicare

Part A covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health care. Most people pay no premium for Part A.

Explore

When can you enroll? An interactive year

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October 15 – December 7 — anyone with Medicare can join, switch, or drop a Medicare Advantage or Part D plan. Changes take effect January 1.

Enrollment windows are federal and the same nationwide. Confirm your personal dates at Medicare.gov or 1-800-MEDICARE.

Sources & further reading
  • CMS — Medicare basics (medicare.gov)

For personalized answers, contact Medicare.gov, 1-800-MEDICARE, or your local SHIP.

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