Medicare Supplement
Medigap, Explained: What Those Letter Plans Really Cover
WAIPAHU, Hawaii — If you've been reading about Medicare and keep bumping into terms like "Plan G," "Plan N," or "Medigap Plan K," you're not alone. Medicare Supplement insurance — often called Medigap — is one of the most misunderstood pieces of the Medicare puzzle. Here's a plain-English guide to what it does, what it doesn't, and how those standardized letters work.
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Key takeaways
- Medigap is private insurance that pays after Original Medicare, covering things like coinsurance, copayments, and hospital deductibles, but it does not replace Part A and Part B.
- In most states, Medigap plans are labeled by letters like G, K, and N, and every plan with the same letter covers the same benefits no matter which company sells it, so shopping is really about comparing price and company, not coverage.
- Medigap generally does not include prescription drug coverage, so many people also look at a stand-alone Part D plan, which for 2026 has a $2,100 out-of-pocket cap and a maximum deductible of $615, with the old coverage gap removed in 2025.
- The best time to buy a Medigap policy is during the six-month Medigap Open Enrollment Period that starts when you turn 65 or older and enroll in Part B, since insurers can't deny you or charge more for health problems during that window, but may use medical underwriting if you apply later.
What Medigap Actually Is
Medigap is private insurance you can buy to help pay some of the costs Original Medicare (Part A and Part B) leaves behind. Think coinsurance, copayments, and hospital deductibles. It works alongside Original Medicare, not instead of it.
Here's the key idea: Medicare pays its share of a covered service first, then your Medigap policy pays its share. You keep your red, white, and blue Medicare card and add a Medigap policy on top.
Medigap is not the same thing as a Medicare Advantage plan. In fact, you can't have both at once. Advantage plans (Part C) replace how you get your Medicare benefits; Medigap simply fills in gaps in Original Medicare.
How the Standardized Letters Work
In most states, Medigap policies are standardized and labeled with letters: A, B, C, D, F, G, K, L, M, and N. (Massachusetts, Minnesota, and Wisconsin standardize their plans differently.)
Standardization means every Plan G sold by every insurance company covers the exact same benefits. A Plan G from Company A covers the same medical costs as a Plan G from Company B. What can differ is the price, the customer service, and whether the company offers extras like household discounts.
That's important. When you compare Medigap policies with the same letter, you're really comparing price and company, not benefits.
A couple of notes:
- 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.
- Plans K and L have lower premiums but include out-of-pocket limits and cost-sharing.
- High-deductible versions of Plan G and Plan F exist for people who want lower monthly premiums.
What Medigap Does Not Cover
Medigap is narrower than a lot of people think. It generally does not cover:
- Prescription drugs (you'd need a separate Part D plan for that)
- Routine dental, vision, or hearing care
- Long-term care (like a nursing home stay beyond what Medicare covers)
- Private-duty nursing
- Eyeglasses or hearing aids
If prescription coverage matters to you — and for most people it does — you'll want to look at a stand-alone Part D drug plan. For 2026, Part D has a $2,100 out-of-pocket cap on covered drugs and a maximum deductible of $615, according to CMS. The old "donut hole" coverage gap was eliminated in 2025, so Part D now has three phases instead of four.
There's also an optional Medicare Prescription Payment Plan that lets you spread your drug costs into monthly payments across the year instead of paying big amounts at the pharmacy counter.
Timing Matters: The Medigap Open Enrollment Window
The best time to buy a Medigap policy is during your six-month Medigap Open Enrollment Period. It starts the month you're 65 or older and enrolled in Part B. During this window, companies can't turn you down or charge you more because of health problems.
Miss that window, and in most states insurers can use medical underwriting — meaning they can ask health questions and potentially deny coverage or raise your rate. This is one of the most costly Medicare mistakes people make, and it's easy to overlook.
Hawaii residents should know their state's specific rules can affect switching later, so it's worth confirming with an unbiased source before you make a change.
Waipahu and Honolulu County
Medicare plan availability — including how many Medicare Advantage and Part D plans are offered — is set at the county level. Waipahu is in Honolulu County, where residents can compare available Advantage and Part D options each year on Medicare.gov's Plan Finder.
Medigap works a little differently. Because it's private supplemental insurance, availability and pricing depend on which insurance companies are licensed to sell Medigap policies in Hawaii — not on county-based Medicare contracts.
Key Dates to Remember
- October 15 – December 7: Medicare Annual Enrollment Period. This is for Part D and Medicare Advantage — not Medigap. You can generally apply for Medigap any time of year, though underwriting rules may apply outside your initial window.
- January 1 – March 31: Medicare Advantage Open Enrollment Period, for people already in an Advantage plan.
Also, if your income is above $109,000 (single filer, 2026), you may pay an IRMAA surcharge on Part B and Part D premiums. That's a program-level rule, not something Medigap changes.
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 Honolulu County
(MA penetration in Honolulu 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
Can I have Medigap and a Medicare Advantage plan at the same time?
Does Medigap cover my prescriptions?
If every Plan G is the same, why do prices vary so much?
- CMS — Medicare basics (medicare.gov)
For personalized answers, contact Medicare.gov, 1-800-MEDICARE, or your local SHIP.