Supplemental Coverage

You know the four parts of Medicare. You know what they cost. You know about the enrollment penalties that never go away. Now comes the decision that determines how much you actually pay when you get sick.

Original Medicare covers 80% of most outpatient costs. The other 20% has no cap. A hip replacement runs $40,000. A cancer diagnosis can run into hundreds of thousands. Twenty percent of those numbers is what you owe, and there is no annual maximum to stop the bleeding. This article fills that gap.

Most people make this choice once, in a narrow window, and live with it for decades. The wrong call doesn’t just cost extra each month. It can lock you out of better coverage permanently.

The Fork in the Road

Every Medicare decision flows from one question: Original Medicare with supplements, or Medicare Advantage?

It determines your doctor network, your financial exposure, your flexibility if you move, and your options if your health changes. Pick one path and the other becomes difficult or impossible to reach later.

	Original Medicare + Supplements	Medicare Advantage
Monthly cost	Higher (Part B + Medigap + Part D)	Lower (often $0 beyond Part B)
Out-of-pocket maximum	Effectively yes, via Medigap	Yes, required by law
Doctor choice	Any Medicare-accepting provider nationwide	Network only (HMO/PPO)
Prior authorization	Rarely	Frequently
Prescription drugs	Separate Part D plan	Usually bundled
Dental/Vision/Hearing	Not included, buy separately	Often included
Predictability	High — you know your costs upfront	Low — depends on what care you need
Switching later	Can move to Advantage annually	Hard to return to Original + Medigap

The right column looks cheaper. For healthy people in a stable location, it often is. But “cheaper” and “better” aren’t the same thing, and the asymmetry at the bottom of that table is the detail that catches people: moving from Original Medicare to Advantage is easy. Moving back is not.

Medigap: Filling the Gaps

Medigap is a private policy that covers what Original Medicare doesn’t pay. You keep Original Medicare as your primary insurer. Medigap picks up deductibles, coinsurance, and excess charges that would otherwise come out of your pocket.

Medigap plans are standardized by letter. Every Plan G sold in your state covers the same things, regardless of the insurance company selling it. The coverage is identical. Only the price and the company’s service differ.

Why Plan G Is the Default

Ten lettered plans exist. Two matter: Plan G and Plan N.

Plan G covers everything except the Part B annual deductible ($257 in 2025). After you pay that $257, your out-of-pocket cost for Medicare-covered services is zero. No 20% coinsurance. No hospital deductibles. No surprise bills from a covered service. For $257 a year, you buy near-total predictability.

Plan N costs $30-$50 less per month than Plan G but requires copays of up to $20 for some office visits and up to $50 for ER visits that don’t result in admission. It also doesn’t cover Part B excess charges (amounts above what Medicare approves). Plan N saves money if you’re healthy and rarely visit doctors. Plan G saves money if you’re not.

For most people enrolling at 65, Plan G is the right starting point. The savings from Plan N are real but modest, and the protection Plan G provides against large, unpredictable costs is the entire reason you’re buying Medigap in the first place.

Pricing Methods Matter More Than the First Premium

Here’s where people get burned. Two Plan G policies from two companies might both cost $150/month when you’re 65. By 75, one costs $200/month. The other costs $350/month. The difference is the pricing method.

Community-rated (no-age-rated): Everyone pays the same premium regardless of age. Your premium at 65 is what you’ll pay at 85, adjusted only for inflation and general rate increases. These policies start higher but grow slowly. They’re the best deal over a 20+ year retirement.

Issue-age-rated: Your premium is based on your age when you buy the policy. It won’t increase because you get older, but it will increase with inflation and rate changes. Better than attained-age, worse than community-rated.

Attained-age-rated: Your premium increases as you age. Cheapest at 65. Most expensive at 85, exactly when you can least afford a premium spike and most need the coverage. This is the method that looks great in the brochure and terrible in practice.

Not every state offers all three methods. Some states require community rating by law (New York, for example). Others let insurers choose. When you’re comparing Medigap quotes, the pricing method is the first thing to check. A $180/month community-rated Plan G beats a $140/month attained-age Plan G over any retirement lasting more than a decade.

To compare plans in your state, start at medicare.gov’s Plan Finder. For free, no-sales-pitch help, call your state’s SHIP (State Health Insurance Assistance Program) counselor. They’ll walk you through available plans, pricing methods, and enrollment. Every state has one.

The Medigap Window

You get one shot at guaranteed Medigap coverage. Six months. That’s it.

Your Medigap open enrollment period starts the month you turn 65 and are enrolled in Part B. For exactly six months, every insurance company must sell you any Medigap policy they offer in your state, at their best price, regardless of your health. Diabetes, cancer history, heart condition: none of it matters during this window. No medical underwriting. No denial. No surcharges.

If you delayed Part B because you had employer coverage (yours or your spouse’s, at a company with 20+ employees), your Medigap window starts when you enroll in Part B, not when you turn 65. A 63-year-old covered under a working spouse’s employer plan can wait until the spouse retires at 67, enroll in Part B then, and get the full six-month Medigap window at that point. The window follows your Part B start date, not your birthday.

After those six months close, the rules change completely. Insurance companies can ask health questions. They can deny you coverage. They can charge higher premiums based on your medical history. They can refuse to cover pre-existing conditions for up to six months. A 66-year-old with well-controlled Type 2 diabetes who missed the window may find that no insurer will sell them Plan G at any price.

This is not hypothetical. Every year, people lose access to Medigap because they didn’t understand the window. They chose Medicare Advantage at 65 thinking they could switch to Original Medicare + Medigap later. Technically, they can switch their Medicare. But getting a Medigap policy with medical underwriting at 72, after a few health scares, ranges from expensive to impossible.

A few states (California, Connecticut, Massachusetts, New York, and others) offer some form of guaranteed issue outside the initial window. Most don’t. Federal law only guarantees it once.

Treat the Medigap open enrollment period as the second most important deadline in Medicare, right behind initial enrollment itself.

Part D: Prescription Drug Coverage

Skip Part D and you’ll pay for it forever. The penalty is 1% of the national base premium ($36.78 in 2025) for every full month you went without creditable coverage. Wait five years and that’s a roughly $22/month surcharge, permanently, on top of whatever premium you eventually pay. It never resets.

The logic for buying Part D even with zero current prescriptions is simple math. A basic Part D plan costs $0-$15/month. The penalty for waiting costs more than that, and you will eventually take medications. The average 65-year-old takes four prescription drugs. The average 80-year-old takes seven. Part D is not optional insurance. It’s a cost you will incur, and the only question is whether you pay the base rate or the base rate plus a permanent penalty.

Choosing a Plan

Part D plans vary wildly. The right one depends on your prescriptions, your pharmacy, and your zip code.

Formulary is the list of drugs the plan covers. Every plan has one, and they differ. A plan that covers your blood pressure medication might not cover your spouse’s inhaler. Medicare’s Plan Finder tool at medicare.gov lets you enter your specific medications and see which plans cover them and at what cost.

Pharmacy network matters if you have a preferred pharmacy. Some plans offer lower copays at preferred pharmacies and higher copays elsewhere. Mail-order pharmacies sometimes offer the deepest discounts.

Premiums vs. total cost: A $0 premium plan with high copays can cost more than a $40/month plan with low copays, depending on what you take. Compare the total annual cost (premiums + copays + deductible), not just the monthly number.

The Coverage Phases

Part D has a structure that looks like it was designed to confuse people. It was probably designed to confuse people.

You pay a deductible (up to $590 in 2025). Then you enter the initial coverage phase, where you pay copays or coinsurance and the plan pays the rest. At $2,000 in true out-of-pocket spending, you hit catastrophic coverage, where your costs drop to $0 for the rest of the year. This $2,000 cap was new in 2025 and is a genuine improvement over the old “donut hole” structure that left people paying full price for drugs in a middle spending range.

Dental, Vision, and Hearing

Original Medicare covers almost nothing here. No routine dental exams. No cleanings. No fillings. No eyeglasses or contact lenses after cataract surgery. No hearing aids. This is a real gap that costs real money.

None of the options here are great. But they’re what exists.

Standalone dental insurance runs $20-$60/month and typically covers preventive care (cleanings, x-rays) at 100%, basic procedures (fillings, extractions) at 80%, and major work (crowns, bridges) at 50%. Annual maximums of $1,000-$1,500 are standard, which means a single crown can exhaust your annual benefit. Worth it if you need regular cleanings. Not worth it if you need major dental work, where a dental discount plan ($80-$200/year for 15-50% off at participating dentists) sometimes saves more.

Vision is simpler. Plans run $10-$20/month, cover annual exams, and include a frame/lens allowance. If you wear glasses, the plan roughly breaks even. Skip it if you don’t.

Hearing is where the real money hides. Traditional hearing aids average $2,000-$7,000 per pair, and Original Medicare covers none of it. Over-the-counter hearing aids (available without a prescription since 2022) run $200-$1,000 for mild to moderate hearing loss and have changed the math for many people. For those who need prescription-grade devices, hearing coverage is one of the strongest reasons to consider Medicare Advantage.

Medicare Advantage: The All-in-One Path

About half of all Medicare beneficiaries now choose Medicare Advantage. One plan, one card, one insurer covering hospital, outpatient, prescriptions, and usually dental, vision, and hearing. Premiums beyond Part B are often $0.

The structural advantage is the out-of-pocket maximum. By law, every Medicare Advantage plan must cap your annual out-of-pocket spending. Most plans set this between $3,000 and $8,000 per year for in-network care. Original Medicare has no such cap without Medigap.

The structural disadvantages are real.

Network restrictions mean you see only the doctors and hospitals in your plan’s network (HMO) or pay more for out-of-network care (PPO). If your cardiologist isn’t in-network, you find a new cardiologist or pay out-of-network rates.

Prior authorization is how Advantage plans control costs. Before certain procedures, tests, or specialist visits, the plan must approve the service. This is the mechanism behind stories of delayed MRIs, denied surgeries, and appeals processes that take weeks. Not every plan is aggressive about denials, but the incentive structure exists: the plan profits by spending less on your care.

Geographic lock-in means your plan works in your plan’s service area. A snowbird splitting time between Michigan and Arizona may find their HMO doesn’t cover that Arizona cardiologist visit. PPO plans offer more flexibility, but at higher cost.

When Advantage Makes Sense

You’re healthy, you live in one place, your doctors are in-network, you want low monthly costs, and you’re comfortable with the network trade-offs. Also: you value having dental, vision, and hearing bundled in without buying separate policies.

When It Doesn’t

You travel frequently. You have complex or chronic health conditions requiring specialists. You want to choose any doctor in the country. You live in a rural area with thin networks. Or you simply want cost predictability — knowing exactly what you’ll pay regardless of what happens to your health.

What This Costs: A Worked Example

Two 66-year-olds. Same health. Same zip code. Different choices.

Path A: Original Medicare + Plan G + Part D

Expense	Monthly	Annual
Part B premium	$185	$2,220
Medigap Plan G (community-rated)	$195	$2,340
Part D premium	$28	$336
Part B deductible	—	$257
Part D deductible + copays (moderate use)	—	$400
Total	~$408/mo base	$5,553

Worst-case year: $5,553. The Medigap policy covers the 20% coinsurance and hospital deductibles. After the Part B deductible, out-of-pocket costs for Medicare-covered services are zero. A $300,000 hospital stay costs nothing beyond what’s in the table. That’s the point.

Add dental insurance ($40/month, $480/year) and vision ($15/month, $180/year), and the total rises to about $6,213/year.

Path B: Medicare Advantage (PPO)

Expense	Monthly	Annual
Part B premium	$185	$2,220
Advantage plan premium	$0	$0
Estimated copays/coinsurance (moderate use)	~$100	~$1,200
Total (typical year)	~$285/mo	$3,420

Worst-case year: Part B premium ($2,220) plus the plan’s out-of-pocket maximum (say $5,500) = $7,720. That’s more than Path A’s worst case.

Scenario	Path A (Original + Medigap)	Path B (Advantage PPO)
Healthy year	$5,553	$3,420
Major surgery	$5,553	$7,720
Cancer treatment (extended)	$5,553	$7,720
10-year cost, 2 bad years	$55,530	$42,800

Path B saves roughly $12,700 over ten years if you have two bad years and eight healthy ones. Path A gives you the same bill every year regardless of what happens. Path A also lets you see any doctor in the country and skip prior authorization.

The question isn’t which costs less. It’s which risk you’d rather carry: higher fixed costs with total predictability, or lower average costs with the chance of hitting the ceiling in a bad year. For people with savings and a low risk tolerance, Path A. For people optimizing monthly cash flow, Path B.

Neither is wrong. Choose with the numbers in front of you, not the marketing brochure.

One more thing: if your spouse turns 65 in a different year, you’ll make these decisions twice on different timelines. Each person gets their own Medigap window, their own Part D enrollment, and their own path choice. A couple doesn’t have to pick the same path. Many don’t.

Where This Breaks

Plans change every year. Your $0-premium Advantage plan can raise copays, drop providers, or exit your market. Your Medigap premium will increase over time. Part D formularies shift. The drug that cost you $10/month last year might cost $45 this year because the plan reclassified it.

Moving states disrupts everything. Medigap policies are state-regulated. Move from Texas to Oregon and your Plan G transfers, but the premium adjusts to Oregon’s rates and you may be subject to medical underwriting if your original state’s rules don’t apply. Medicare Advantage plans are regional. Move and your plan probably doesn’t follow. You’ll need to enroll in a new plan in your new state during a Special Enrollment Period.

Switching from Advantage back to Original Medicare is the big risk. You can switch during the annual Open Enrollment Period (October 15 to December 7). But switching back to Original Medicare without a Medigap policy leaves you with the 20% coinsurance gap and no cap. And getting a Medigap policy outside your initial open enrollment window means medical underwriting. If you’ve developed health conditions during your years on Advantage, you may be denied or charged significantly more. Some states offer annual guaranteed-issue Medigap windows. Most don’t.

Long-term care is still not covered. Neither path covers custodial nursing home care, and the median annual cost of a private room exceeds $116,000. This is a separate planning problem that supplemental coverage does not solve.

Medicare’s Open Enrollment Period runs October 15 through December 7 every year. Use it. Fifteen minutes on medicare.gov comparing next year’s costs can save hundreds of dollars.

What’s Next

Coverage decisions don’t exist in isolation. How you withdraw retirement income, when you start Social Security, and how you manage your tax bracket all affect what Medicare charges you in IRMAA surcharges and what coverage you can afford.

Required Minimum Distributions covers the tax time bomb most retirees ignore, and Social Security Timing walks through when to claim and why most people get it wrong.