Medicare Advantage
How Medigap's Letter Plans Work in Mount Pleasant
MOUNT PLEASANT, S.C. — If you've started shopping for a Medicare Supplement policy here in the Lowcountry, you've probably noticed the alphabet soup: Plan A, Plan B, Plan G, Plan N, and a few others. Those letters aren't marketing labels. They're standardized benefit packages set by federal rules, which means a Plan G sold in Mount Pleasant covers the same core benefits as a Plan G sold in Greenville — or in Denver, for that matter.
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Key takeaways
- Medigap plans are labeled by letters like A, B, G, and N, and federal rules require the same letter to offer the same core benefits no matter which company sells it or where you live.
- Since the benefits inside each lettered plan are fixed, what actually differs between insurers is the monthly premium, customer service, and how rates increase over time.
- Your Medigap Open Enrollment Period is a one-time six-month window that starts 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.
- After that six-month window ends, insurers in South Carolina can generally use your health history to charge more or deny coverage, and since Medigap doesn't include drug coverage, most people pair it with a separate Part D plan.
A quick primer for Mount Pleasant readers
That standardization is meant to make comparing policies easier. Here's how to think about it.
What Medigap actually does
Medicare Supplement Insurance, often called Medigap, is a private policy that works alongside Original Medicare (Part A and Part B). After Medicare pays its share of a covered service, your Medigap policy helps pay some of what's left — things like coinsurance, copayments, and deductibles.
A few important points from Medicare.gov:
- Medigap only works with Original Medicare. It does not work with Medicare Advantage.
- Medigap does not include prescription drug coverage. For that, you'd need a separate Part D plan.
- You pay a monthly premium for the Medigap policy in addition to your Part B premium.
How the standardized letters work
In most states, including South Carolina, Medigap policies are sold as lettered plans: A, B, C, D, F, G, K, L, M, and N. Each letter is a fixed package of benefits defined by the federal government. Insurance companies choose which letters to sell, and they set their own premiums — but they cannot change what's inside a given letter.
A couple of details worth knowing:
- Plans C and F are only available to people who became eligible for Medicare before January 1, 2020. If you aged into Medicare after that date, those two letters are off the table.
- Plans K and L have out-of-pocket limits built in and cover a smaller share of certain costs.
- High-deductible versions of Plan G and Plan F exist for people who want a lower premium in exchange for paying more before coverage kicks in.
Because the benefits inside each letter are identical from company to company, the main things that vary are the monthly premium, the company's customer service, and how the company raises rates over time.
The Mount Pleasant angle
Mount Pleasant is in Charleston County, where Medigap policies are regulated by the South Carolina Department of Insurance and sold by private carriers licensed in the state. Availability of specific letters and carriers is a county-level matter, so two neighbors — one in Mount Pleasant and one across the Ravenel Bridge in downtown Charleston — generally see the same menu of options.
To see what's currently offered in your ZIP code, the plan finder at Medicare.gov lets you filter by location.
Timing matters more than most people realize
The single most important thing to understand about Medigap is your Medigap Open Enrollment Period. This is a one-time, six-month window that starts the month you're 65 or older and enrolled in Part B. During that window, insurance companies must sell you any Medigap policy they offer at their best available rate, regardless of your health history.
After that window closes, in most cases insurers in South Carolina can use medical underwriting — meaning they can look at your health and either charge more or decline to cover you. That's why the decision about whether to start with Medigap or Medicare Advantage is one worth thinking through carefully, ideally before that six-month clock runs out.
Where Part D fits in
Because Medigap doesn't include drug coverage, most people who choose Medigap also enroll in a stand-alone Part D prescription drug plan. A few figures to keep in mind:
- The Part D out-of-pocket cap is $2,100 in 2026.
- The maximum Part D deductible is $615.
- The old coverage gap (the "donut hole") was eliminated in 2025; Part D now has three phases.
- The Medicare Prescription Payment Plan lets you spread your drug costs out in monthly installments if that helps with cash flow.
- IRMAA surcharges — the extra amount higher earners pay on Part B and Part D — begin above $109,000 in income for a single filer in 2026.
The Annual Enrollment Period for Part D and Medicare Advantage runs October 15 through December 7 each year. The Medicare Advantage Open Enrollment Period runs January 1 through March 31.
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 Charleston County
(MA penetration in Charleston 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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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.
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The parts of Medicare
Good to know
Frequently asked questions
Do I have to buy Medigap when I first sign up for Medicare?
Can I switch from Medicare Advantage to Medigap later?
If Plan G is standardized, why do premiums vary so much between companies?
- CMS — MA/Part D Landscape & Plan Finder data
For personalized answers, contact Medicare.gov, 1-800-MEDICARE, or your local SHIP.