Medicare Supplement
Understanding Medigap: What the Plan Letters A–N Really Mean
FORT COLLINS, Colorado — If you're new to Medicare or helping a parent sort through their options, you've probably run into a wall of letters: Plan A, Plan G, Plan N, and more. These are Medicare Supplement plans, better known as Medigap. And once you understand how the lettering system works, the whole picture gets a lot less confusing.
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Key takeaways
- Medigap is private insurance that works with Original Medicare to help cover leftover costs like coinsurance, copayments, and some deductibles, but it can't be used with a Medicare Advantage plan.
- In most states, Medigap comes in 10 standardized lettered plans (A, B, C, D, F, G, K, L, M, N), and every plan with the same letter offers the exact same set of benefits no matter which company sells it, so shopping mainly comes down to comparing price and service.
- Your 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 must sell you any plan they offer at their best rate during that window regardless of health history.
- Outside that window, insurers in most states can ask health questions, charge more, or deny coverage, and since Medigap doesn't cover prescription drugs, most people pair it with a separate Part D drug plan.
Here's a plain-English guide to what Medigap does, why the letters matter, and how it fits with the rest of Medicare in 2026.
What Medigap actually does
Medigap is private insurance that works alongside Original Medicare (Part A and Part B). It doesn't replace Medicare — it fills in some of the out-of-pocket costs that Medicare leaves behind, like coinsurance, copayments, and certain deductibles.
For example, Part A has a hospital deductible, and Part B generally pays 80% of covered outpatient services, leaving you responsible for the other 20% with no built-in cap. A Medigap policy can pick up some or all of those leftover costs, depending on which lettered plan you choose.
One important note: Medigap only works with Original Medicare. If you're enrolled in a Medicare Advantage plan (Part C), you can't also use a Medigap policy.
Why the letters exist
Back in the early 1990s, Medigap plans were a mess. Every insurance company sold something different, and shoppers had no easy way to compare. Congress fixed that by requiring insurers to standardize their Medigap offerings into lettered plans.
Today, in most states — including Colorado — Medigap plans come in 10 standardized versions: A, B, C, D, F, G, K, L, M, and N. (Massachusetts, Minnesota, and Wisconsin do things a little differently.)
Here's the key idea: every Plan G sold by every company covers the exact same set of benefits. The federal government sets what each letter includes. What can differ from one insurer to another is the price, the customer service, and extras like household discounts — not the core benefits.
How the lettered plans differ
Each letter represents a different bundle of benefits. Some plans cover almost everything Medicare leaves behind. Others cover less in exchange for lower monthly premiums. A few use cost-sharing, meaning you pay a share of costs up to a yearly limit and then the plan takes over.
A couple of things worth knowing:
- Plans C and F 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.
- Plan G has become one of the most popular options for newer enrollees because it covers a broad range of gaps.
- Plan N typically has a lower premium but asks you to pay small copays at the doctor and emergency room.
- Plans K and L cap your yearly out-of-pocket spending, then pay 100% of covered services after that.
Because the benefits inside each letter are fixed by law, comparing plans really comes down to comparing prices and the company behind the policy.
When you can buy a Medigap policy
Timing matters more with Medigap than a lot of people realize. Your best window is your Medigap Open Enrollment Period — a six-month stretch that starts the month you're 65 or older and enrolled in Part B. During that window, insurers must sell you any Medigap plan they offer at their best available rate, regardless of your health history.
Outside that window, in most states, insurers can use medical underwriting. That means they can ask health questions, charge more, or turn you down. There are limited situations that give you "guaranteed issue" rights later on, but the safest strategy is to understand your options before that first six-month window closes.
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.
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 Larimer County
(MA penetration in Larimer County)
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.
How Medigap fits with Part D and 2026 Medicare changes
Medigap doesn't cover prescription drugs. For that, most people with Original Medicare add a stand-alone Part D drug plan.
A few 2026 figures worth knowing as you plan:
- The Part D out-of-pocket cap is $2,100 in 2026. Once your covered drug spending hits that ceiling, you pay $0 for the rest of the year on covered drugs.
- The Part D maximum deductible is $615.
- The old "donut hole" coverage gap was eliminated in 2025. Part D now has three phases instead of four.
- The Medicare Prescription Payment Plan lets you spread your drug costs over monthly payments instead of paying big bills at the pharmacy counter.
- IRMAA — the income-based surcharge on Part B and Part D — kicks in above $109,000 for a single filer in 2026.
- Annual Enrollment runs October 15 through December 7. The Medicare Advantage Open Enrollment Period runs January 1 through March 31.
Medigap enrollment is not tied to those windows, but the drug plan you pair with it is.
What's available in the Fort Collins area
Fort Collins is in Larimer County, where residents choosing Original Medicare plus a Medigap policy generally have access to a wide range of insurers licensed to sell the standardized lettered plans in Colorado. Because the benefits inside each letter are identical from company to company, the shopping work is really about pricing and service — not benefit design.
For a current list of Medigap plans and insurers available in your ZIP code, the plan finder at Medicare.gov is the official source.
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Enrollment windows are federal and the same nationwide. Confirm your personal dates at Medicare.gov or 1-800-MEDICARE.
Good to know
Frequently asked questions
Is Medigap the same as Medicare Advantage?
If all Plan G policies cover the same things, why do prices vary so much?
Do Medigap plans cover dental, vision, or hearing?
- CMS — Medicare basics (medicare.gov)
For personalized answers, contact Medicare.gov, 1-800-MEDICARE, or your local SHIP.