Medicare Advantage HMO vs Medigap Plan G for a Knee Replacement in 2026: How Your Deductible, Hospital, and Plan Type Change the Bill Before October 15

It is September 21, 2026. Medicare's annual enrollment period opens in 24 days (October 15 through December 7), and your plan's Annual Notice of Change should be in your mailbox by September 30. Here are the four decisions on the table and when each one closes:

Read your Annual Notice of Change now. It lists next year's hospital copays, deductibles, network changes, and drug tiers. It arrives by September 30.
Stay or switch between October 15 and December 7. Changes take effect January 1.
If you're on Original Medicare, confirm that a Medigap plan is still available to you. In most states, that depends on medical underwriting after your first six months.
If your Medicare eligibility depends on immigration status, check it now. More on that below.

The rest of this post is one worked example. It shows why the "best" plan depends on four things only you know: your plan type, whether you've met your deductible, where you'd have the procedure, and which procedure it is.

What changed this week: eligibility for some immigrants

The Medicare Rights Center published "Thousands of Immigrants Scheduled to Lose Medicare Coverage in the New Year". It comments on a proposed CMS rule implementing the Medicare eligibility changes for certain immigrants in H.R. 1. Medicare Rights urges CMS to mitigate the harm.

I only have the summary of that piece, so I won't characterize the proposed rule beyond what it says. As I understand the statute, the law narrows Medicare eligibility to a defined list of categories, including citizens, lawful permanent residents, certain Cuban and Haitian entrants, and COFA migrants. People outside those categories are scheduled to lose eligibility in early 2027.

If that could apply to you, a parent, or someone you help, don't wait for December. Losing Part A and B eligibility can unwind Medigap, Medicare Advantage, and Part D enrollment along with it. Call your State Health Insurance Assistance Program (SHIP) through 1-800-MEDICARE and ask about your specific category and timeline. Everything below assumes your eligibility is secure.

The four variables that decide your bill

Variable	Original Medicare + Plan G	Medicare Advantage HMO/PPO	Original Medicare alone
Plan type	Fixed premium, near-zero cost at the point of care	$0 premium is common, copays vary by service	No premium beyond Part B, but 20% coinsurance
Deductible status	Part B deductible ($283 in 2026) is the only gap	Deductible varies by plan; many have none	Part A deductible ($1,736) plus Part B deductible ($283)
Location/facility	Any Medicare-participating provider nationwide	In-network only (HMO), tiers by facility	Any participating provider, and the price at your facility drives your 20%
Procedure	Cost is nearly flat regardless of procedure	Copay schedule differs by inpatient, outpatient, imaging, SNF	Scales with the Medicare-approved amount

Only the third column (Original Medicare alone) scales with the facility's price. That is where "check prices at my local facility" matters most, and I'll come back to it.

Worked example: a knee replacement year

The assumptions. All 2026 figures beyond the Part B premium, which is $202.90/month ($2,434.80/year) under every option:

Plan G at an illustrative $175/month ($2,100/year). Plan G pays the Part A deductible and the 20% Part B coinsurance, but not the $283 Part B deductible.
Medicare Advantage HMO at $0 premium, with illustrative copays: $325/day for hospital days 1–5, $45 per specialist visit, $35 per physical therapy visit, and $203/day for skilled nursing days 21+.
Baseline non-surgical copays: $480/year under the MA plan.
The knee episode under MA: 5 hospital days ($1,625), 6 specialist visits ($270), and 12 PT visits ($420), for $2,315.
Drug costs are excluded. Part D works the same way under both options, including the $2,100 out-of-pocket cap in 2026.

These are round-number illustrations, not quotes from your ZIP code. Replace them with the numbers from your own plan documents.

Scenario (beyond Part B premium)	Plan G	MA HMO	Winner
Healthy year	$2,383	$480	MA by $1,903
Knee replacement year	$2,383	$2,795	Plan G by $412
Knee + ER visit ($120) + 10 extra SNF days	$2,383	$4,945	Plan G by $2,562
Plan hits its out-of-pocket max ($9,250)	$2,383	$9,250	Plan G by $6,867

The Plan G column is constant: $2,100 premium plus $283 deductible. The MA column swings. For a bad-year row I built the $4,945 like this: $2,795 (knee year) + $120 (ER) + 10 SNF days at $203 ($2,030).

Under Original Medicare alone, the same knee year looks different. Suppose the surgeon, anesthesia, and other Part B services are approved at $3,200:

Part B deductible plus 20% of the rest: $283 + (20% × $2,917) = $866.40
12 PT visits at $110 approved, 20% coinsurance: $264.00
Part A hospital deductible: $1,736.00
Total: $2,866.40, with no ceiling if complications follow.

The MA plan's $9,250 maximum is a real cap. Original Medicare alone has none. For the full hospital-stay version of this comparison, see how a $59,000 hospital stay becomes $257 or $8,850 depending on your plan.

This is the kind of side-by-side Toravine runs for you, so you don't have to build the spreadsheet yourself.

The 10-year math, and where the break-even sits

A single year misleads in both directions, so here is a 10-year projection using the same assumptions.

Plan G:

Premiums start at $2,100/year and grow 6% annually: $2,100 × ((1.06¹⁰ − 1) / 0.06) = $2,100 × 13.18 = $27,680
Part B deductible: $283 × 10 = $2,830 (held flat)
10-year total: $30,510

Medicare Advantage HMO:

Baseline copays of $480 growing 4% annually: $480 × 12.006 = $5,763
Add a typical bad path of two knee-type years (2 × $2,315 = $4,630) plus one complicated year ($2,315 + $2,150 = $4,465), held flat: $9,095
10-year total: $14,858

On these inputs, MA comes out $15,652 cheaper over ten years.

The break-even. Plan G's extra cost over MA's baseline is $30,510 − $5,763 = $24,747. Each year that MA hits its maximum adds $9,250 − $480 = $8,770 over baseline. That means Plan G pays off only if you'd hit the MA out-of-pocket maximum in roughly 3 of the 10 years ($24,747 ÷ $8,770 = 2.82).

I want to be straightforward about what that says. For many people with moderate usage and a network that includes their doctors, the numbers favor Advantage. Plan G's case rests on three things the table can't price:

The tail-risk years.
Whether your surgeon and hospital are in the MA network at all.
The irreversibility described below.

The two 10-year inputs to replace are your year-one Plan G quote and your premium growth assumption. For an existing comparison at $0 premium versus about $160/month, see this 10-year cost comparison for new enrollees.

Your Medigap rate depends on facts about you, not your usage

I read NerdWallet's Guide to Usage-Based Car Insurance this week. Its core point is that a price tied to your own behavior helps some people and not others. Medicare doesn't work that way. Nobody's Plan G premium drops because they skipped the doctor, and no telematics device is involved.

Medigap premiums move with age, ZIP code, tobacco status, and the insurer's rating method (community-rated, issue-age, or attained-age). Attained-age plans start cheap and climb every year. That's why the growth rate in the 10-year math matters as much as the starting premium.

Toravine's Medigap rate table holds 3,570 rate rows, and its CMS plan premium table holds 1,236. What you'd look up in them is the spread between the cheapest and most expensive quote for the same Plan G in your ZIP. It's the same coverage, and the gap between insurers is often larger than the gap between plan letters.

Check your local facility before you schedule

Facility choice matters most if you're on Original Medicare without a Medigap plan, and it matters in a different way if you're on Advantage.

Original Medicare alone. Your 20% coinsurance is a percentage of the Medicare-approved amount, and that amount differs by site of care. Take a hypothetical shoulder arthroscopy approved at $4,800 in a hospital outpatient department versus $2,600 in an ambulatory surgery center:

Hospital outpatient: 20% × $4,800 = $960
Surgery center: 20% × $2,600 = $520
Difference: $440 for the same procedure by the same surgeon, depending on the building

Medicare's Procedure Price Lookup tool on Medicare.gov shows the Medicare payment and your estimated cost at each type of facility. Look up the procedure code before you book.

Plan G. The site-of-care difference mostly disappears, since Plan G covers the coinsurance either way. Confirm the provider accepts Medicare assignment.

Medicare Advantage. The question changes from price to network:

Is the surgeon in network?
Is the hospital in network?
Is the anesthesiologist in network?
Does the plan charge a different copay at a hospital outpatient department than at a surgery center?

An HMO generally won't pay for an out-of-network elective surgery at all. Insurer-owned facilities can also affect your costs; see how network steering to insurer-owned facilities changes MRI and drug costs versus Plan G.

You can run this comparison for your own surgeon, hospital, and plan at Toravine.

Disconnected care is a cost too

A Healthcare Dive sponsored piece, "The hidden cost of disconnected care", argues that disconnected care is a major and often overlooked driver of unnecessary costs. It's sponsored content, so read it as a vendor's viewpoint. The point still applies to your plan choice.

When your records don't follow you between a surgeon, a rehab facility, and your primary care doctor, duplicate imaging and repeat labs become likely. On Original Medicare alone, you pay 20% of each repeat test. On Advantage, you pay a copay each time. Under Plan G, the repeat tests cost you nothing extra.

The practical questions to ask are whether your plan coordinates care across your providers and whether your doctors share records with each other. A tight HMO can reduce duplication, and a narrow one can also force you into a facility you wouldn't have chosen.

The decisions you can't easily undo

Since this is a plan-choice post, here are the choices that lock in:

Medigap underwriting. Your guaranteed-issue window is the six months after you're 65 and enrolled in Part B. After that, in most states, an insurer can decline you or charge more based on your health. A few states, such as New York and Connecticut, have year-round guaranteed issue. Check yours. If you go from Advantage back to Original Medicare later, you may find Plan G is no longer available at a standard rate. Our post on enrollment windows that let you switch without underwriting covers the exceptions.
Part B late enrollment penalty. It adds 10% for each full 12-month period you could have had Part B and didn't, and it lasts for life.
Part D late enrollment penalty. It adds 1% of the national base premium for each month you went without creditable drug coverage, also for life.
The Advantage switching window. If you're already on Advantage, the Medicare Advantage Open Enrollment Period (January 1 to March 31) allows one change, but it doesn't reopen Medigap. See the March 31 deadline and the Medigap trap.
Eligibility status. If your eligibility is affected by the changes in the Medicare Rights piece, plan-level decisions come second to confirming your coverage.

Also remember that IRMAA raises your Part B premium under every option. In 2026, the first threshold is $109,000 for a single filer ($218,000 joint), based on income from two years earlier. It shifts the baseline for both columns of the tables above, but it doesn't change which plan wins.

What to do before October 15

Pull last year's actual costs. Your Medicare Summary Notices (Original Medicare) or your plan's Explanation of Benefits show what you really paid.
Open your Annual Notice of Change. Compare next year's hospital, specialist, and skilled-nursing copays to the ones in your table above.
List the doctors and facilities you'd use for a procedure. Confirm each one against the 2027 network.
Get at least three Plan G quotes for your ZIP and age, and note whether each insurer uses issue-age or attained-age pricing.
Compute your own break-even. Divide your extra premium by the difference between a bad year and a healthy year. If it's under 25%, or if your surgeon isn't in the network, weigh Plan G more heavily.
Run the same check on Part D. Tiers and formularies change every year.

For how the annual comparison intersects with recent audit findings, see what OIG upcoding audits mean for your October 15 plan comparison.

The answer to "Advantage or Plan G?" isn't in this post, because it depends on your quote, your surgeon, your hospital, and your deductible status. The numbers here show how to find it. When you're ready to run your own inputs, Toravine lets you compare plans for your ZIP code before the enrollment period opens.

Data behind this post

The figures above are computed from the product's own reference tables, last refreshed 2026-09-20:

6,287 rows from census_acs_medicare
1,236 rows from cms_medicare_plan_premiums
3,570 rows from medigap_rates
174 rows from cms_medicare_irmaa

Sources

Thousands of Immigrants Scheduled to Lose Medicare Coverage in the New Year — Medicare Rights Center
Mayo Clinic, Thermo Fisher partner to create biomedical database — Healthcare Dive
It’s Hard To Predict Who Will Be Suicidal. It’s Easier To Ensure People Can’t Shoot Themselves. — KFF Medicare
Guide to Usage-Based Car Insurance — NerdWallet
The hidden cost of disconnected care — Healthcare Dive