Medicare Supplement

Medigap in St. Charles: how the standardized letter plans are built and why they matter

If you live in St. Charles and you have Original Medicare, you have probably heard the term "Medigap" tossed around at the coffee shop or a church supper. It is short for Medicare Supplement Insurance, and it is one of the more misunderstood corners of the Medicare world. The letter names — Plan A, Plan G, Plan N and the rest — throw people off. They sound like grades. They are not.

The short version, for St. Charles readers

Medigap plans are standardized by the federal government. That means a Plan G sold by one insurance company covers the same core benefits as a Plan G sold by another. What can differ is the price and the customer service, not the medical benefits.

What Medigap actually does

Original Medicare (Part A and Part B) pays a big share of your hospital and doctor bills, but not all of it. You still owe deductibles, coinsurance and copays, and there is no yearly cap on how much you can be asked to pay out of pocket.

A Medigap policy sits behind Original Medicare and picks up some — or in some letters, most — of those leftover costs. Depending on the letter you choose, it may pay the Part A hospital coinsurance, the Part B coinsurance, the first three pints of blood, hospice coinsurance, skilled nursing facility coinsurance, and in a few cases, foreign travel emergency care.

One thing Medigap does not do: it does not cover prescription drugs. For that, most people add a stand-alone Part D drug plan.

Why the letters exist

Before the federal government stepped in, Medicare supplement policies came in every shape and size, and comparing them was a headache. Congress fixed that by creating a set of standardized benefit packages, each labeled with a letter. Today, in most states including Missouri, you can shop from these letters: A, B, C, D, F, G, K, L, M and N.

Here is the important part: the benefits inside each letter are set by law. A Plan G from one company must cover the same things as a Plan G from another. So when you compare plans of the same letter, you are really comparing the price, the company's reputation, and how they handle billing and customer service.

A couple of notes worth knowing:

• Plans C and F, which used to be very popular, are only available to people who were eligible for Medicare before January 1, 2020. If you became eligible after that, those two are off the menu.
• Plans K and L work a little differently — they cover a percentage of costs and have their own yearly out-of-pocket limit.
• Plan N has some copays for office visits and emergency room trips that do not lead to admission.

How Medigap fits with the rest of your coverage

Medigap is designed to pair with Original Medicare. It cannot be used with a Medicare Advantage plan. If you are in an Advantage plan and want to switch to Original Medicare plus a Medigap policy, that is a bigger move than it sounds like — and depending on when you do it, the insurer may be allowed to ask health questions before selling you a policy.

That is why timing matters. Your one guaranteed window to buy any Medigap plan sold in your area, at the best available rate for your age, is the Medigap Open Enrollment Period. It is a six-month window that begins the month you are 65 or older and enrolled in Part B. During that window, insurers cannot turn you down or charge you more because of your health.

After that window closes, you can still apply — but in most cases the insurer can look at your health history. Missouri does have a helpful rule called the "anniversary" guaranteed issue right that lets people already in a Medigap plan switch to the same letter with another company each year around their policy anniversary. Your local SHIP counselor (see below) can walk you through it.

What Medigap does not replace

It is easy to think Medigap is a one-stop policy. It is not. To round out your coverage, most people on Original Medicare also carry:

• A Part D prescription drug plan for medications. In 2026, Part D has a $2,100 annual out-of-pocket cap and a maximum deductible of $615. The old "donut hole" coverage gap was eliminated in 2025, and there is now an optional Medicare Prescription Payment Plan that lets you spread drug costs across the year.
• Separate dental, vision or hearing coverage, if you want it. Medigap plans generally do not include those benefits.

Also worth remembering: if your income is above certain thresholds, you may pay an IRMAA surcharge on top of your Part B and Part D premiums. For 2026, that starts above $109,000 for a single filer.

How to think about choosing a letter

Since the benefits are fixed by letter, the choice comes down to two questions: how much of the cost-sharing do you want the plan to handle, and how much are you willing to pay in premium for that peace of mind?

A plan that covers more usually costs more each month. A plan that covers less leaves you with more predictable monthly costs but bigger bills when you actually use care. Neither approach is "right" — it depends on your budget, your health, and how much financial surprise you can tolerate.

St. Charles is in St. Charles County, and the Medigap letters available to Missouri residents are set at the state level, not by city. So the menu of letters is the same whether you live near Main Street or out toward Cottleville. What changes from insurer to insurer is the price.

Where to get unbiased help

You do not have to figure this out on your own, and you do not have to rely only on what an agent tells you. Two free, trustworthy resources:

• Medicare.gov — the official site. It has a Medigap plan finder and clear descriptions of every letter.
• 1-800-MEDICARE — available 24/7 for questions.
• Missouri CLAIM — the state's SHIP (State Health Insurance Assistance Program). CLAIM counselors are trained volunteers who give one-on-one help at no cost. They do not sell anything.