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Medicare Part B Excess Charges in Sioux Falls 2026: The 15% Billing Gap, Which Plans Block It, and What to Know

Non-participating providers can legally bill you 15% above Medicare's rate — with no annual ceiling — but two Medigap plans and all five local PPOs handle it very differently.

Big Sioux Benefits Data Desk

Published July 16, 2026 · 9 min read · Sourced from CMS.gov

Most Medicare beneficiaries learn about excess charges the hard way: on an Explanation of Benefits that shows an amount owed well above the familiar 20%. Here's what causes that gap, how big it can get for Sioux Falls' 39,532 Medicare beneficiaries, and exactly which plan choices eliminate the risk.

Every figure in this article comes from public federal data — the CMS 2025 Medicare Parts A & B cost-sharing fact sheet, the CMS Medigap standardization guide (Publication 02110), the CMS PY2026 plan landscape, and CDC PLACES 2023 county health data for Minnehaha County.

How Medicare Part B assignment works — the three-tier system

Every provider who sees Medicare patients falls into one of three categories under federal law:

• Participating providers — sign a yearly agreement accepting Medicare's approved amount as payment in full. Medicare pays 80%, you pay 20% (the coinsurance), nothing more.
• Non-participating providers — accept Medicare but have not signed the participating agreement. They may bill you up to 15% above the Medicare-approved amount, on top of your 20% coinsurance.
• Opt-out providers — have formally exited Medicare. They can set any fee they choose; Medicare pays nothing. You bear the full cost.

The term "limiting charge" describes the legal ceiling a non-participating provider can bill: 115% of the Medicare-approved rate. It's a ceiling, not a default — many non-participating providers bill less. But the risk of the full 15% overage is real, and it stacks on top of your standard cost-sharing with no annual cap under Original Medicare.

The 15% excess charge math — a real example

Here's what the billing looks like at a concrete service value, using the federal Part B cost-sharing parameters for 2025 (the figures currently in effect for 2026 coverage):

Source: CMS 2025 Medicare Parts A & B Premiums and Deductibles (Fact Sheet). Example uses $1,000 Medicare-approved amount for illustration. Actual approved amounts vary by service and location.

The Plan N gap is not a one-time problem. A beneficiary who sees a cardiologist, an orthopedist, and a neurologist — each a non-participating provider — over a single year could face $150 or more in excess charges per visit, with no ceiling. Multiply by several visits per specialty and the exposure compounds quickly.

Which Medigap plans cover excess charges — and which don't

Of the 8 standardized Medigap plans currently available to new enrollees in South Dakota, only two cover Part B excess charges. Here's the full picture:

Source: CMS — Choosing a Medigap Policy (Publication 02110) (CMS Publication 02110). Plans C and F not available to those first eligible for Medicare on/after Jan 1, 2020.

Plan G is the strongest option for new enrollees who want excess-charge protection — it covers the Part B coinsurance, the Part A deductible, skilled nursing facility (SNF) coinsurance, and foreign travel emergencies, in addition to excess charges. Plan D covers most of the same gaps except excess charges and has a lower premium in many cases, making the comparison between G and D essentially a bet on how often you'd encounter non-participating providers.

Plan N deserves special attention here. It's often marketed as "Plan G minus" because of its lower premium — and it is, except it drops two protections: excess charges and Part B excess (it adds instead a $20 office-visit copay and a $50 ER copay). Beneficiaries who see a lot of specialists should run the math: if a lower Plan N premium saves $600 per year but excess charges add up to $400+, the savings shrink fast.

Medicare Advantage users: already protected

If you're enrolled in one of the 5 standard Medicare Advantage PPOs in Sioux Falls, excess charges simply don't apply. Inside a Medicare Advantage plan, your benefits are governed by your plan's contracts with its provider network — those contracts set the copays and coinsurance you'll pay, and the mechanism of "billing 15% above the Medicare fee schedule" has no place in that framework.

Here are the 5 Sioux Falls Medicare Advantage PPOs for 2026:

Source: CMS Medicare Advantage / Part D Landscape (PY2026) & CMS Medicare Advantage & Part D Star Ratings (2026), Minnehaha County, PY2026.

All five plans carry a 3.5★ CMS quality rating in 2026. The trade-off isn't about excess charges (you're covered either way with Advantage) — it's about the annual out-of-pocket maximum versus the freedom to see any Medicare-accepting provider that Medigap offers. For the excess-charge question specifically, Medicare Advantage is a clean answer.

Who in Sioux Falls faces the most exposure

Excess charges matter most when you visit specialists repeatedly — and Minnehaha County's health profile shows exactly where that risk concentrates. Among 39,532 Medicare beneficiaries:

Source: CDC PLACES: Local Data for Better Health, County 2023 (2023, Minnehaha County adults, model-based prevalence).

High blood pressure (31.7%) typically requires quarterly cardiology follow-ups. Arthritis (22.9%) means orthopedist visits. Depression (22.3%) brings psychiatrist and therapist appointments. Each specialist encounter with a non-participating provider carries its own potential excess charge. A single beneficiary managing three chronic conditions and seeing specialists for each could face hundreds of dollars in excess charges over a year under Original Medicare with Plan N — but zero with Plan G or any Advantage plan.

The Sioux Falls provider landscape: Sanford and Avera

The good news for Sioux Falls beneficiaries: both major health systems operate as large, Medicare-integrated institutions where the vast majority of physicians accept Medicare assignment.

Source: CMS Hospital Compare — Overall Star Ratings.

Sanford USD Medical Center holds a 5-star CMS quality rating and Avera McKennan a 4-star — both strong. For routine in-system care, excess charges are unlikely. The real risk appears with independent specialists, out-of-town consultants, anesthesiologists, or radiologists who sometimes operate within a hospital but under separate contracts. These providers may not accept assignment even when the facility does. Always ask any new provider — including specialists referred by your primary care doctor — whether they accept Medicare assignment before your appointment.

The IRMAA + excess charge stack for higher-income beneficiaries

Beneficiaries with higher incomes pay an Income-Related Monthly Adjustment Amount (IRMAA) surcharge on top of the standard Part B premium. For these beneficiaries, excess charges add a third layer of exposure. Here are the 2025 Part B premium brackets by income:

Source: CMS 2025 Medicare Parts A & B Premiums and Deductibles (Fact Sheet) & SSA Medicare Premiums: Rules for Higher-Income Beneficiaries. IRMAA uses a 2-year income lookback; 2026 coverage reflects 2024 income.

IRMAA applies regardless of which Medicare path you choose — Original Medicare, Medigap, or Medicare Advantage. A beneficiary in the top tier pays $628.90/month in Part B premium alone. Stacking an uncapped excess-charge exposure on top (Plan N) adds meaningful risk. For IRMAA-affected beneficiaries considering Medigap, the Plan G premium is often a small price for eliminating all Part B cost uncertainty.

What to watch going into AEP 2026 (October 15–December 7)

1. If you have Plan N, ask yourself how many non-participating specialists you've seen or expect to see. If excess charges appear on your Explanations of Benefits, compare the cost of upgrading to Plan G against what you've paid in excess charges — and factor in the underwriting question.
2. If you're turning 65 in the next 6 months, you're in or approaching your guaranteed-issue Medigap window. Plan G versus Plan N versus a $0 Medicare Advantage PPO are the three real options — the excess-charge question is one differentiator in that decision.
3. If you're on a Medicare Advantage PPO, verify your specialists are still in-network for 2026. Annual Notice of Change letters (mailed in September) will confirm any network changes.
4. If you see independent anesthesiologists, radiologists, or surgical assistants, ask about assignment in advance. These are the providers most commonly operating in hospitals yet billing separately — and most likely to be non-participating.
5. Check the Part D interaction: the 2026 Part D out-of-pocket cap is $2,100, which helps high drug users — but that cap doesn't apply to Part B excess charges. A beneficiary managing expensive infused medications under Part B still has full excess-charge exposure under Original Medicare.

How we know all this: Big Sioux Benefits runs every article through a data desk that cross-references CMS cost-sharing fact sheets, the standardized Medigap plan matrix (42 CFR §403.205), CMS plan landscape and star ratings, CMS Hospital Compare, and CDC local health data — built by Strategic AI Architects. Every figure here is from a public federal dataset. This is education, not advice; confirm your plan, costs, and eligibility with a licensed agent or Medicare.gov. We take no payment from any carrier to feature a plan.