What Is Medigap? A Plain-English Guide to Medicare Supplement Plans for Houston (2026)

What is Medigap? Medigap is the everyday name for Medicare Supplement Insurance — a private insurance policy you buy to help pay the “gaps” that Original Medicare (Part A and Part B) leaves behind, such as the hospital deductible, the 20% coinsurance on doctor visits, and the daily cost of a long hospital stay. It rides alongside Original Medicare: Medicare pays its share of a covered service first, then your Medigap policy pays some or all of what is left, depending on the lettered plan you choose. It does not replace Medicare, and it is not Medicare Advantage.

If you have lived in Houston long enough, you have seen the mailbox flood — the glossy envelopes from carriers, the dinner-seminar invitations near the Galleria, the booths at the H-E-B on Bellaire during the fall. Somewhere in all that noise, two words keep surfacing: “Medigap” and “Medicare Supplement.” People in Bellaire, Pasadena, The Heights, and Spring keep asking the same thing at our kitchen-table appointments — are those two different products, or the same thing? They are the same thing. And for the tens of thousands of Harris County residents who get their care at the Texas Medical Center, a Medigap policy is often what turns an unpredictable medical bill into a predictable monthly premium. This plain-English guide explains what Medigap is, what it covers, what it does not, and — critically for Texans — why the timing of when you buy it matters more here than in most states.

What is Medigap, and is it the same as Medicare Supplement?

Yes — Medigap and Medicare Supplement Insurance are two names for the exact same product. “Medicare Supplement Insurance” is the formal name used in federal law and on official documents; “Medigap” is the nickname nearly everyone uses in conversation, because the policy quite literally fills the gaps in Original Medicare. When a carrier, an agent, or the Texas Department of Insurance refers to either term, they mean the same private policy.

Here is the mechanic in plain language. Original Medicare — Part A (hospital insurance) and Part B (medical insurance) — pays most of the cost of covered services, but not all of it. You are left holding deductibles, copayments, and coinsurance, and Original Medicare has no annual out-of-pocket maximum on its own. A Medigap policy steps in after Medicare pays. For a covered service, Medicare pays its approved share first, then your Medigap plan pays some or all of the remaining Medicare-approved costs, based on the lettered plan you bought. The result for most people is fewer surprise bills and a more predictable monthly cost.

A few ground rules apply to every Medigap policy sold in Texas. You must be enrolled in both Part A and Part B to have one. Each Medigap policy covers exactly one person — spouses each need their own policy. And a Medigap policy is guaranteed renewable, meaning the insurer cannot drop you for getting sick or using your benefits, as long as you pay the premium. To see how Medigap fits with the rest of your coverage choices, start with our Medicare overview and our Medicare Supplement Plans page.

Why are Medigap plans labeled with letters, and are they really identical across companies?

Medigap plans are labeled with letters because federal law standardizes them into ten plan designs, and within each letter the benefits are identical no matter which company sells it. In most states, including Texas, the standardized plans are A, B, C, D, F, G, K, L, M, and N. (These letters are completely separate from the “parts” of Medicare — Part A, Part B, Part D. A Medigap “Plan A” is not the same as Medicare “Part A.”)

This standardization is the single most important consumer-protection feature of Medigap, and it is exactly what trips people up in the mailbox blizzard. Because a Plan G is a Plan G everywhere, the benefits do not change from company to company — only the premium, the company’s service reputation, and the pricing method change. According to Medicare.gov’s plan-benefit comparison, every insurer that sells a given letter must cover the same standardized basket of benefits for that letter.

The table below summarizes the core benefits for the plans Houston shoppers ask about most — Plan G, Plan N, Plan F (closed to new enrollees), and the cost-sharing Plans K and L. Read it across each row to see what share of that gap the plan covers.

*Plan F is available only to those eligible for Medicare before January 1, 2020. **Plan N pays the Part B coinsurance, except for copayments of up to $20 for some office visits and up to $50 for emergency-room visits that do not result in an inpatient admission. Plans K and L also carry an annual out-of-pocket limit after which they pay 100% for the rest of the year. Source: Medicare.gov, Compare Medigap plan benefits.

For a deeper look at one specialized design — the high-deductible version, where you pay more out of pocket before coverage kicks in — see our high-deductible Medigap plans page.

What does Medigap cover — and what does it leave out?

Medigap covers the cost-sharing gaps in Original Medicare — things like the Part A hospital deductible, the Part A daily coinsurance on long stays, the 20% Part B coinsurance on doctor and outpatient services, skilled nursing facility coinsurance, and (on most plans) a portion of foreign-travel emergency care. What it does not cover is just as important to understand before you buy.

Three exclusions surprise people the most:

• No prescription drug coverage. Modern Medigap plans do not include outpatient prescription drugs. To cover your medications, you enroll in a separate stand-alone Medicare Part D prescription drug plan. This is a key structural point: a Medigap + Part D pairing is a common way Houston retirees build their coverage. Per Medicare.gov, Medigap policies sold today cannot include drug coverage.
• No routine dental, vision, or hearing. Medigap does not pay for routine dental cleanings, eyeglasses, or hearing aids. Those are handled separately — for example, through a stand-alone dental/vision plan.
• No long-term custodial care, and generally no coverage outside what Medicare approves. Medigap pays its share only after Medicare approves a service. If Medicare does not cover something (such as long-term custodial nursing-home care), Medigap generally does not cover it either.

The chart below shows, in round terms, how a Medigap Plan G changes a Houston retiree’s exposure on the two biggest 2026 Original Medicare deductibles compared with having no supplement at all.

Does Medigap work with Medicare Advantage, or only Original Medicare?

Medigap works only with Original Medicare (Parts A and B). It is illegal for anyone to sell you a Medigap policy if they know you are enrolled in a Medicare Advantage plan, unless you are leaving that plan and returning to Original Medicare. The two systems are designed as alternatives to each other, not companions.

Here is why. A Medicare Advantage plan (sometimes called Part C) is a bundled, all-in-one alternative to Original Medicare offered by a private insurer — it has its own networks, copays, and an annual out-of-pocket maximum, and it often includes drug coverage and extras. Medigap, by contrast, is a supplement that sits on top of Original Medicare and pays your share of Medicare-approved costs. You cannot use a Medigap policy to pay the copays or coinsurance in a Medicare Advantage plan; the Medigap policy simply has nothing to attach to in that system.

So the choice usually comes down to two coverage paths, and you pick one:

• Path 1 — Original Medicare + Medigap + a stand-alone Part D drug plan. Broad access to any provider that accepts Medicare nationwide, predictable cost-sharing, no networks.
• Path 2 — Medicare Advantage. A bundled private plan, usually with networks and an annual out-of-pocket cap, often including drug and extra benefits.

Neither path is universally “right” — it depends on your doctors, your medications, your travel, and your budget. We walk Houston clients through both sides on our Medicare Advantage and Medicare Plans pages, and at the kitchen table. (If you are also weighing income-based programs, our Medicare vs. Medicaid comparison is a useful companion read.)

When is the right time to buy Medigap, and what is the 6-month Open Enrollment Period?

The strongest time to buy Medigap is during your Medigap Open Enrollment Period (OEP) — a one-time, six-month window that starts automatically the first month you are both 65 or older and enrolled in Medicare Part B. During this window you have a guaranteed issue right: any insurance company selling Medigap in Texas must sell you any policy it offers, cannot turn you down for health reasons, cannot charge you more because of your health history, and cannot make you wait for coverage to start (with a limited pre-existing-condition exception if you did not have prior creditable coverage).

That phrase — no medical underwriting — is the heart of it. Medical underwriting is when the insurer reviews your health history and can deny you, charge you more, or delay coverage based on what they find. During your 6-month OEP, they cannot do any of that. Outside it, in Texas, they usually can. The Medicare.gov guidance on when to buy Medigap is blunt about this: this window gives you your strongest opportunity to enroll regardless of health.

A few timing details Houston clients often miss:

• The window is keyed to your Part B effective date, not your 65th birthday alone. If you delayed Part B because you were still working with employer coverage, your 6-month Medigap OEP does not begin until your Part B actually starts.
• It is once-in-a-lifetime for the age-65 trigger. It does not reset each year and it does not come back.
• It is separate from the Medicare Annual Enrollment Period (October 15 – December 7) that you hear about every fall — that period is for Part D and Medicare Advantage, not for guaranteed-issue Medigap.

Check your own dates on our Medicare Eligibility page, then let us confirm exactly when your window opens.

Why does Medigap timing matter more in Texas than in other states?

Medigap timing matters more in Texas because Texas has no “birthday rule” and no annual guaranteed-issue window to fall back on. In a handful of states — California and Oregon, for example — a “birthday rule” lets people switch to an equal or lesser Medigap plan each year around their birthday without medical underwriting. Texas offers no such annual do-over. Once your one-time 6-month Open Enrollment Period closes, buying or switching a Medigap policy in Texas generally means going through medical underwriting, where the insurer can review your health and decline you, rate you up, or impose a waiting period.

That single difference changes the stakes of the calendar. In a birthday-rule state, a missed window is an inconvenience you can correct next year. In Texas, a missed window can mean you are locked into your current coverage path or facing higher prices if your health has changed. The Texas Department of Insurance Medicare Supplement guide lays out the protections that do and do not apply in Texas, and confirms that outside your open-enrollment or a guaranteed-issue situation, companies can use underwriting.

There are still specific federal guaranteed-issue situations that can apply in Texas even outside the 6-month window — for example, if your employer retiree coverage ends, if a Medicare Advantage plan leaves your area, or in certain trial-right scenarios. But those are narrow, time-limited, and triggered by particular events. They are not a general annual reset. The table below contrasts the Texas reality with the birthday-rule states so you can see why the calendar carries more weight here.

The chart below illustrates the practical consequence — the share of Medicare beneficiaries who, nationally, can face denial or higher premiums when applying for Medigap outside a protected window, which is precisely the underwriting exposure Texans carry once their one-time window closes.

Why can’t I buy Plan C or Plan F anymore?

If you became eligible for Medicare on or after January 1, 2020, you cannot buy Medigap Plan C or Plan F — federal law closed those two plans to newly eligible people. The change came from the Medicare Access and CHIP Reauthorization Act of 2015 (MACRA), which barred newly eligible beneficiaries from buying any Medigap plan that pays the Part B deductible. Plans C and F were the two that paid it, so they were closed to the newly eligible.

Three things follow from this rule, and they matter for Houston shoppers:

• If you were eligible for Medicare before January 1, 2020, you can keep a Plan C or Plan F you already have, and you may still be able to buy one where available.
• If you became eligible on or after January 1, 2020, Plan C and Plan F are off the table for you. The closest equivalents are Plan G (identical to Plan F except you pay the Part B deductible — $283 in 2026) and Plan N.
• Plan G has become the default pick for many new enrollees precisely because it offers the most comprehensive coverage still open to them, with only the modest annual Part B deductible left for you to pay.

The phase-out, confirmed in the official Medicare “Choosing a Medigap Policy” guide, is why you will see Plan G and Plan N dominate today’s Houston conversations while Plan F shows up mainly for people who were already eligible before 2020.

How are Medigap premiums priced in Texas?

Medigap premiums in Texas are set using one of three pricing methods, and the method a company uses changes how your premium behaves as you age. Because every Plan G (or Plan N, or any letter) covers the identical benefits, the pricing method and the carrier’s rate are most of what separates one quote from another. Texas allows all three methods, including attained-age pricing, which is the most common — and the one that rises with age.

The three methods:

• Community-rated (no-age-rated). Everyone with the same plan pays the same base premium regardless of age. Your premium does not go up just because you get older (it can still rise with inflation).
• Issue-age-rated. Your premium is based on the age you were when you bought the policy. It does not increase simply because you are getting older — buying younger locks in a lower starting basis.
• Attained-age-rated. Your premium is based on your current age and rises as you get older. These often start lower at 65 but climb over time. This is the most common method offered in Texas.

The line chart below illustrates the core idea: an attained-age policy can start lower at 65 but climb steadily with age, while an issue-age policy holds a flatter age path. The exact dollars depend on the carrier and inflation — this shows the shape of the two pricing methods, not a quote.

Why this matters: two companies can sell the identical Plan G in Houston, but if one uses attained-age pricing and the other uses issue-age pricing, the one that looks cheaper at 65 may not be the cheaper one at 78. Inflation and the carrier’s own rate history affect all three methods on top of the age mechanics. The Medicare.gov explainer on how Medigap policies are priced walks through the same three methods. When we compare quotes for a Houston client, we look past the first-year premium to how the policy is likely to behave over a decade or two.

How do you choose and enroll in a Medigap plan in Houston?

Choosing a Medigap plan comes down to four decisions, in order: pick your coverage path, pick the plan letter, compare carriers on that letter, and time your application to your guaranteed-issue window. Because the benefits within each letter are fixed by law, the work is less about hunting for a “different” policy and more about matching the right letter and carrier to your health, budget, and doctors.

A practical sequence we use with Houston and Harris County clients:

1. Confirm you want Original Medicare + Medigap rather than Medicare Advantage. This is the fork in the road; everything else follows from it.
2. Choose your plan letter. For most people newly eligible after 2020, the real comparison is Plan G vs. Plan N — Plan G covers more (everything but the Part B deductible), Plan N trades small office and ER copays for a typically lower premium.
3. Compare carriers on that one letter. Since the benefits are identical, compare premium, pricing method (attained vs. issue vs. community), the carrier’s rate-increase history, and service reputation.
4. Add a stand-alone Part D plan. Medigap has no drug coverage, so pair it with a Part D plan that fits your medication list and your Houston pharmacy.
5. Apply within your 6-month Open Enrollment Period to lock in guaranteed issue and avoid Texas underwriting.

This is exactly the conversation our team has every week at our North Houston office and our South Houston office. We are licensed in Texas, we know which carriers file competitive Medigap rates here, and we help you read the fine print so you are not deciding from a stack of mailers alone. When you are ready, contact us and we will map your dates and your options together.

Frequently asked questions

Wise Insurance Agency is a licensed insurance agency in the State of Texas. The information here is general guidance and not a substitute for plan-specific advice. We do not offer every plan available in your area. Any information we provide is limited to those plans we do offer in your area. Please contact Medicare.gov, 1-800-MEDICARE, or your local State Health Insurance Assistance Program (SHIP) to get information on all of your options. Medigap plan availability, premiums, pricing methods, and the standardized benefits within each letter are set by federal and Texas law and by individual carriers; 2026 Medicare figures reflect CMS data as published as of the date this article was written. Verify current rules and rates with the Texas Department of Insurance, CMS, or a licensed agent before making any election.