Original Medicare WISeR Prior Authorization vs Medicare Advantage HMO vs Medigap Plan G: What a Knee Procedure Costs at a Hospital vs a Surgery Center in 2026

You have a procedure on the calendar, or one your doctor is starting to mention. Before you schedule it, there are four questions whose answers change your bill:

1. Which plan are you on? Original Medicare alone, Original Medicare with Medigap Plan G, or a Medicare Advantage (MA) HMO or PPO.
2. Where do you live? Since January 2026, six states have a new layer of prior authorization inside Original Medicare.
3. Where will the procedure happen? A hospital outpatient department and an ambulatory surgery center can bill very different amounts for the same operation.
4. Have you met your Part B deductible yet this year?

Nobody can answer these for you in general terms. That is why the same knee procedure can cost you about $283 or more than $1,500, depending on the plan and the building.

What changed in 2026: prior authorization reached Original Medicare

Original Medicare has historically used very little prior authorization. That has been one of its practical advantages over Medicare Advantage. In its September 2026 Medicare Watch item, "New Records Show Medicare WISeR AI Prior Authorization Model Causing Inappropriate Denials of Care," the Medicare Rights Center describes a change. In January 2026, CMS launched a six-year model called WISeR (Wasteful and Inappropriate Service Reduction). It uses technology-assisted review to require prior authorization for a set of selected services in Original Medicare. The Medicare Rights Center reports that newly obtained records show inappropriate denials of care under the model.

Here is what that means in practice:

• WISeR applies to specific services and specific states, not to all of Original Medicare. Check CMS's current list for your state and your procedure. Lists like this can change.
• If you are in a WISeR state and your service is on the list, your provider has to get a determination before the service. A denial can delay care or leave you deciding whether to proceed without a payment guarantee.
• If you are in MA, WISeR doesn't apply. Your plan's own prior authorization rules do, and those have long been broader. For more on that, see our post on how CMS's AI prior authorization pilot changes denial costs and when Original Medicare costs less.

So the old shorthand, "Original Medicare has no prior auth, Medicare Advantage does," is now incomplete. It depends on your state and the specific service.

Why your health profile makes this a pricing question

The Medicare Rights Center's item "Medicare Beneficiaries With Multiple and Complex Health Needs Face Challenges" summarizes new KFF polling on access and affordability problems among adults with multiple or complex conditions, including older Medicare beneficiaries. The polling points to a pattern many beneficiaries already know from experience. The more services you use in a year, the more your plan's structure matters, including its deductibles, coinsurance, networks and authorization rules.

If you have three chronic conditions and see two specialists, a knee procedure is not a one-off event. It sits alongside imaging, therapy, drugs and follow-up visits. A plan that looks cheap in a light year can look very different in a heavy one.

The same cost pressure shows up outside Medicare. KFF Health News reports in "Economic Frustration Tests Trump's Standing With Rural Voters, New KFF-AP Poll Finds" that rural voters rank the cost of living and the cost of health care among the top issues they want candidates to address. In "As Health Insurance Costs Soar, Healthcare Workers Also Feel the Pinch," a couple who work in health care saw premiums rise by hundreds of dollars a month and chose to go uninsured. Those two stories are about voters and workers, not beneficiaries. But they point to the same reality. Health costs are squeezing budgets, and if you're approaching 65 from an ACA plan, the Medicare choices you make now will set your cost baseline for years.

The worked example: one outpatient knee procedure, three plans, two facilities

Here is a scenario built on illustrative assumptions. I am not quoting a specific hospital's price. Replace every number with your own before you rely on it.

Assumptions

• 2026 Part B premium: $202.90/month ($2,434.80/year)
• 2026 Part B deductible: $283, not yet met
• Medigap Plan G premium: $178/month ($2,136/year), in the range we see in our comparisons of Plan G premiums
• Standalone Part D premium: $40/month ($480/year)
• Outpatient knee procedure, Medicare-approved amount: $6,400 at a hospital outpatient department, $3,100 at an ambulatory surgery center
• MA HMO: $0 plan premium (drug coverage included), $350 copay for hospital outpatient surgery, $250 at a surgery center, in-network

Original Medicare, no Medigap

Part B pays 80% after the deductible, and you owe the rest.

• Hospital: $283 + 20% of ($6,400 − $283) = $283 + $1,223.40 = $1,506.40
• Surgery center: $283 + 20% of ($3,100 − $283) = $283 + $563.40 = $846.40

Original Medicare + Medigap Plan G

Plan G pays the 20% Part B coinsurance but not the Part B deductible.

• Hospital: $283
• Surgery center: $283

Medicare Advantage HMO

• Hospital: $350
• Surgery center: $250

The full-year picture

Cost item	Original + no Medigap	Original + Plan G	MA HMO ($0 premium)
Part B premium	$2,434.80	$2,434.80	$2,434.80
Plan premium (Medigap or MA)	$0	$2,136	$0
Part D premium	$480	$480	$0 (bundled)
Procedure cost at hospital	$1,506.40	$283	$350
Total, hospital	$4,421.20	$5,333.80	$2,784.80
Procedure cost at surgery center	$846.40	$283	$250
Total, surgery center	$3,761.20	$5,333.80	$2,684.80

On these assumptions, the MA HMO wins in a year with one outpatient procedure. That is not the whole story, and it's not an argument for MA.

1. The MA number only holds if the plan approves the procedure and your surgeon and facility are in network. If the plan denies authorization or your surgeon is out of network, the math changes.
2. The Plan G number is your ceiling for most Part A and B cost-sharing, not just for this procedure. A hospital stay, a complication, or a second surgery adds almost nothing to Plan G, while an MA plan's out-of-pocket maximum for 2026 can be as high as $9,250 in network (the federal cap). You are paying $2,136 a year for protection against the bad year. If you want the full comparison across years, see our 10-year cost comparison for MA vs Plan G.
3. The no-Medigap column looks decent here, but it has no ceiling. The hospital-vs-surgery-center gap alone is $660. Unlimited exposure on a bigger event is the real risk.

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

Where the facility changes the answer

The table shows that under Plan G, the facility barely matters, with a difference of $0 on this procedure. Under an MA HMO it moved by $100 in this example. Under Original Medicare with no Medigap it moved by $660. Where you get care matters most if you are in the plan structure that shifts the most cost onto you.

That is why the closing question in this post is a local one. In Toravine's work with the four datasets behind our plan analysis (Census ACS Medicare, CMS Medicare plan premiums, Medigap rates, and CMS IRMAA, 11,267 rows in total), the consistent finding is that Medicare costs are not one national number. Premiums, Medigap rates and plan availability vary by state and county, and no single figure fits everyone. Our figures above are illustrative, so use your own local prices.

Before you schedule, do three things:

• Ask your surgeon's office for the facility options and the billing codes (CPT codes) for the procedure at each one.
• Ask each facility for the Medicare allowed amount and whether it bills as a hospital outpatient department or an ambulatory surgery center. Hospital-owned departments can add a separate facility fee.
• Ask whether prior authorization is required. In a WISeR state on Original Medicare, ask if the procedure is on the model's list. On MA, get the authorization number in writing before the date.

We've seen this cost pattern before in our analysis of hospital versus surgery center Part B coinsurance, if you want the longer version.

The irreversible decisions hiding inside this comparison

If this comparison makes you want to switch plans, know which switches can be undone and which cannot.

• Medigap underwriting. Outside your Medigap open enrollment window, and outside guaranteed-issue situations, most states allow insurers to use medical underwriting. If you have a knee that needs surgery, you may be declined or charged more. Switching from MA back to Original Medicare and a Medigap plan is the classic trap. It is easy to leave Original Medicare and hard to get back to Plan G. Our post on the Medicare Advantage open enrollment period and the Medigap trap walks through the timing.
• Late enrollment penalties. If you're turning 65 off an ACA plan, missing your Part B window means a penalty that lasts as long as you have Part B. The math is in our post on turning 65 on an ACA plan with no subsidies.
• Annual lock-ins. MA and Part D changes generally happen during the fall Annual Enrollment Period (October 15 to December 7), and changes take effect January 1. A mid-year procedure decision can't be fixed by switching plans mid-year, apart from limited special enrollment situations.

Also note the IRMAA surcharge. Higher-income beneficiaries pay more than $202.90 for Part B, which changes every column in the table above. Use your own tax-year income when you model it.

A short decision guide

You're on Original Medicare + Plan G, in a WISeR state. Your cost exposure for the procedure is likely low. Your risk is delay if the service needs authorization. Ask your provider to submit early and know your appeal rights.

You're on Original Medicare with no Medigap. Facility choice is the biggest lever you have. Get two prices in writing and pick the lower-cost site, if your surgeon works at both. Then take a hard look at whether you want protection against the next bill.

You're on an MA HMO. Confirm the surgeon, the facility and any anesthesia provider are all in network, and that authorization is on file. Check your plan's out-of-pocket maximum and how much of it you've already used this year.

You have multiple chronic conditions. Don't judge on the one procedure. Add up the specialists, imaging, therapy and drugs you expect. The KFF findings on complex needs suggest this is where plan structure tends to matter most.

You're approaching 65 from an ACA plan. Compare before your enrollment window closes. The premium pressures described in KFF Health News's healthcare-worker story are a reason to plan the transition on purpose, not by default.

What to do this week

1. Write down your plan type, your state, whether you have met your Part B deductible, and your procedure's CPT code.
2. Get allowed amounts from each candidate facility.
3. Ask about prior authorization: WISeR if you're on Original Medicare in a participating state, your plan's rules if you're on MA.
4. Mark October 15 on your calendar and re-compare your own plan before then.

You can model your own plan, deductible status and local facility prices at Toravine. The point isn't to find a universally cheapest plan. It's to find the one that fits your state, your doctors and the facilities near you, and to do it before you schedule the procedure, not after the bill arrives.

This post is educational and uses illustrative figures. Your actual costs depend on your plan documents, your provider's billing, and current CMS rules. Confirm details with your plan, 1-800-MEDICARE, or your State Health Insurance Assistance Program (SHIP) counselor.

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

• Medicare Beneficiaries With Multiple and Complex Health Needs Face Challenges — Medicare Rights Center
• New Records Show Medicare WISeR AI Prior Authorization Model Causing Inappropriate Denials of Care — Medicare Rights Center
• Journalists Discuss What RFK Jr. Recently Told the Anti-Vaccine Group He Founded — KFF Medicare
• Economic Frustration Tests Trump’s Standing With Rural Voters, New KFF-AP Poll Finds — KFF Medicare
• As Health Insurance Costs Soar, Healthcare Workers Also Feel the Pinch — KFF Medicare