Medicare Supplement

How Medigap plan letters work for Detroit Medicare enrollees

DETROIT — If you have Original Medicare and you've started shopping for extra coverage, you've probably run into a wall of letters: Plan A, Plan G, Plan N, Plan K. These are Medicare Supplement plans, often called Medigap, and the letters aren't random. They're standardized by the federal government to make comparing coverage easier — once you know how to read them.

Understanding the standardized Medigap plan letters

Here in Detroit, which sits in Wayne County, retirees have a range of Medigap options to sort through. But the good news is that a Plan G sold by one company must cover the same core benefits as a Plan G sold by another. That's the whole point of the letter system.

What Medigap actually does

Original Medicare (Part A and Part B) covers a large share of your hospital and doctor costs, but not all of them. You're still responsible for deductibles, coinsurance, and copays — and there's no yearly out-of-pocket limit built into Original Medicare itself.

A Medigap policy is private insurance you buy on top of Original Medicare to help cover those leftover costs. Depending on the letter you choose, it may pay all or part of your Part A hospital coinsurance, Part B coinsurance, the first three pints of blood, hospice coinsurance, and more.

Medigap works only with Original Medicare. If you're enrolled in a Medicare Advantage plan, you can't also use a Medigap policy.

Why the letters exist

Before standardization, insurance companies could design Medigap policies any way they wanted, and shoppers had no good way to compare. Congress changed that. Today, in most states, Medigap plans come in ten standardized letters: A, B, C, D, F, G, K, L, M, and N.

Here's the key idea: the benefits inside each lettered plan are set by federal rules. A Plan N from one carrier covers the exact same core services as a Plan N from another. What can differ is the monthly premium, the company's customer service, and how they set their rates over time.

Plans C and F, which covered the Part B deductible, are no longer available to people who became eligible for Medicare on or after January 1, 2020. If you were eligible before that date, you may still be able to buy them.

How to read the letters at a glance

Plans stack from lighter coverage to more comprehensive coverage:

• Plan A covers the basic benefits every Medigap plan must include.
• Plans B, D, G, M, and N add more coverage on top of that base, with Plan G being one of the most comprehensive options available to new enrollees.
• Plans K and L are cost-sharing plans — you pay a percentage of certain costs until you hit a yearly out-of-pocket limit, then the plan pays 100% for the rest of the year.
• Plan N covers most gaps but asks for small copays for some office and emergency room visits.

For a side-by-side chart of every letter and what it covers, Medicare.gov has an official comparison tool.

Your best time to enroll

Timing matters more with Medigap than almost anything else in Medicare. Your Medigap Open Enrollment Period is a one-time, six-month window that starts the first 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 the best available rate, regardless of your health history. Outside that window, in most cases, insurers can use medical underwriting — which means they can charge you more or turn you down based on pre-existing conditions.

Michigan has some additional consumer protections, but the federal six-month window is still the safest time to shop.

What Medigap does not do

A common and costly mix-up: Medigap does not cover prescription drugs. For medications, you'll need a stand-alone Medicare Part D plan. In 2026, Part D has a $2,100 annual out-of-pocket cap and a maximum deductible of $615. There's also an optional Medicare Prescription Payment Plan that lets you spread your drug costs across the year in monthly installments.

Medigap also doesn't cover routine dental, vision, hearing aids, or long-term custodial care.