Medicare Supplement
Medigap Letters Explained: A Denver Reader's Guide
DENVER — If you have Original Medicare and you've started looking at ways to fill in what it doesn't pay, you've probably run into a wall of letters: Plan A, Plan G, Plan N, and more. That alphabet is Medicare Supplement Insurance — better known as Medigap — and it's designed to be easier to compare than it looks at first glance.
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Key takeaways
- Medigap plans are labeled with letters like A, B, G, K, and N, and federal rules require plans with the same letter to cover the same core benefits no matter which company sells them.
- Plan C and Plan F are only available to people who became eligible for Medicare before January 1, 2020.
- Your Medigap Open Enrollment Period is a one-time, six-month window starting the month you turn 65 or older and enroll in Part B, and during this time insurers must sell you any plan they offer at their best rate regardless of your health.
- Medigap enrollment rules are separate from the Medicare Annual Enrollment Period (October 15 – December 7) and the Medicare Advantage Open Enrollment Period (January 1 – March 31).
Making sense of Medigap in Denver
Here in Denver, which sits in Denver County, Medigap works the same way it does across most of the country. The federal government standardizes what each lettered plan must cover, so a Plan G sold by one insurer covers the same core benefits as a Plan G sold by another. What can differ is the premium and the company's customer service.
What Medigap actually does
Medigap is private insurance that works alongside Original Medicare (Part A and Part B). After Medicare pays its share of a covered service, your Medigap policy picks up some or all of what's left — things like coinsurance, copayments, and, depending on the plan, the Part A hospital deductible.
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 choose one path or the other.
- It does not cover long-term care, dental, vision, or hearing aids on its own.
Medigap is meant to reduce the surprise of out-of-pocket costs when you use Original Medicare — not to replace it.
Why the letters exist
Before standardization, Medigap policies were all over the map, and shopping was confusing. Today, in most states including Colorado, Medigap plans are sold in standardized versions labeled 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.)
Because the benefits inside each letter are set by federal rules, you can compare Plan G from Insurer X to Plan G from Insurer Y and know you're comparing apples to apples on coverage. The differences come down to price, the company's reputation, and how they handle rate increases over time.
You can see the full benefit chart on the official Medicare site at medicare.gov.
How the letters differ, in plain terms
Without naming any specific insurer or premium, here's the general idea:
- Plans A and B offer more basic coverage.
- Plan G is a popular choice for people newly eligible, because it covers most gaps except the annual Part B deductible.
- Plan N typically has lower premiums in exchange for small copays at some visits.
- Plans K and L share costs with you up to a yearly out-of-pocket limit, then pay 100% for the rest of the year.
- High-deductible versions of some plans exist for people who want lower monthly premiums and are comfortable paying more upfront if they use care.
Which letter fits best depends on your health, budget, and how much predictability you want.
Timing matters more than most people realize
The single most important thing to know about Medigap is your Medigap Open Enrollment Period. It's a one-time, 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 plan they offer at their best available rate, regardless of your health history.
Outside that window, in most states, insurers can use medical underwriting — meaning they can charge more or turn you down based on your health. Colorado has some additional protections in certain situations, but the safest time to shop is during your open enrollment window.
Note: Medigap has its own enrollment rules. It is not tied to the Medicare Annual Enrollment Period (October 15 – December 7) or the Medicare Advantage Open Enrollment Period (January 1 – March 31), which apply to Advantage and Part D plans.
How Medigap fits with Part D in 2026
Because Medigap doesn't include drug coverage, most people with Medigap also enroll in a stand-alone Part D plan. A few 2026 figures worth knowing:
- The Part D out-of-pocket cap is $2,100 for the year.
- The Part D maximum deductible is $615.
- The old "donut hole" coverage gap has been eliminated; Part D now has three phases.
- The Medicare Prescription Payment Plan lets you spread your drug costs across the year in monthly payments if that helps your budget.
- IRMAA surcharges on Part B and Part D premiums begin above $109,000 in income for a single filer in 2026.
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 Denver County
(MA penetration in Denver 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.
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The parts of Medicare
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When can you enroll? An interactive year
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 I move from Denver to another state, can I keep my Medigap plan?
Can I switch Medigap plans later?
- CMS — Medicare basics (medicare.gov)
For personalized answers, contact Medicare.gov, 1-800-MEDICARE, or your local SHIP.