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Medicare Part B Outpatient Costs in Sioux Falls 2026: The 20% Gap — and Three Ways to Close It

The $257 deductible is the footnote. The uncapped 20% coinsurance is the real story — and there are three ways to cap it before it surprises you.

Big Sioux Benefits Data Desk

Published July 8, 2026 · 10 min read · Sourced from CMS.gov

Under Original Medicare alone, your Part B out-of-pocket costs have no annual ceiling — a fact that surprises many Sioux Falls beneficiaries who assumed the $2,100 Part D cap applied to doctor bills too. The Part D cap (new for 2026) only covers prescription drugs. Your outpatient medical costs — specialist visits, imaging, lab work, outpatient surgery — remain subject to a flat 20% coinsurance forever, on top of the $257 annual deductible.

Every figure in this article comes from public federal datasets: the CMS 2025 Medicare Parts A & B Premiums and Deductibles (Fact Sheet), the Social Security Administration — Medicare Premiums: Rules for Higher-Income Beneficiaries, the CMS Medigap Publication 02110, the CMS PY2026 plan landscape, and CDC PLACES county health data. No invented numbers.

What Part B actually covers — and why it matters

Most people think of Medicare as "hospital" (Part A) and "doctor" (Part B), but Part B is far broader than that. It covers everything outpatient — the category where the majority of Medicare spending happens for people with managed chronic conditions:

• Physician and specialist visits (primary care, cardiologist, endocrinologist, orthopedics, mental health)
• Diagnostic tests — blood panels, urinalysis, cardiac monitoring
• Imaging — X-ray, MRI, CT scan, ultrasound
• Outpatient surgery — cataract removal, joint injections, minor procedures
• Durable medical equipment (DME) — CPAP machines, wheelchairs, blood glucose monitors
• Outpatient mental health services — individual and group therapy
• Chemotherapy and dialysis when done in an outpatient setting
• Preventive services — annual wellness visit, cancer screenings, flu shots (covered at $0 when your provider accepts Medicare assignment)

With 31.7% of Minnehaha County adults managing high blood pressure and 10% with diagnosed diabetes, most Medicare beneficiaries in Sioux Falls use Part B services regularly — not occasionally. That makes the 20% cost structure worth understanding precisely.

The uncapped 20%: what the math actually looks like

Here is the Part B cost-sharing structure for 2026. The annual deductible is small; the coinsurance has no ceiling.

To make the exposure concrete, here is what 20% costs at different levels of outpatient use — all figures are arithmetic on the published CMS coinsurance rate:

Coinsurance rate and deductible: CMS 2025 Medicare Parts A & B Premiums and Deductibles (Fact Sheet). Scenario amounts are illustrative calculations using the published 20% rate — not CMS average-cost projections.

The local health profile that drives outpatient risk

The CDC PLACES data for Minnehaha County shows why this is not a theoretical risk for most Sioux Falls Medicare beneficiaries. These are the chronic-condition prevalence rates that send people to specialists, imaging centers, and outpatient labs:

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

Hypertension at 31.7% means cardiology follow-ups, regular blood pressure monitoring, and echocardiograms. Diabetes at 10% means quarterly endocrinology visits, A1C labs, eye exams, and foot care — all outpatient, all subject to the 20%. Depression at 22.3% means regular outpatient mental health visits. None of these are one-time events; they are year-over-year Part B exposure.

IRMAA: your Part B premium may already be higher than $185

Before your 20% coinsurance even begins, you pay the Part B monthly premium. For most Sioux Falls beneficiaries the standard rate is $185.00/month. But for higher earners — based on your 2024 income, with a 2-year lookback — the Income-Related Monthly Adjustment Amount (IRMAA) adds a surcharge:

Source: Social Security Administration — Medicare Premiums: Rules for Higher-Income Beneficiaries and CMS 2025 Medicare Parts A & B Premiums and Deductibles (Fact Sheet) (2025 published brackets; verify current-year amounts at SSA.gov).

Key IRMAA points for Sioux Falls beneficiaries:

• The 2-year lookback is real. Your 2026 premium reflects 2024 income — meaning a high-income year that's already two years behind you still affects what you pay now.
• New retirees often get surprised. A high final working year can trigger IRMAA your first year on Medicare.
• You can appeal. If a qualifying life event (retirement, divorce, death of a spouse, loss of income) reduced your income since the lookback year, file SSA Form 44 for a modified adjusted gross income redetermination.
• A $0-premium Medicare Advantage plan doesn't protect you from IRMAA. You still owe the full Part B premium — IRMAA and all — regardless of your Advantage plan's premium.

Option 1 — Medigap Plan G or Plan N: pay the 20% away

A Medigap (Medicare Supplement) policy sits on top of Original Medicare and pays the cost-sharing Medicare doesn't cover. For Part B specifically, two plans stand out:

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

Plan G is the most popular choice for people new to Medicare in 2026. It covers 100% of the Part B 20% coinsurance, the Part A deductible, SNF coinsurance, and Part B excess charges. The only gap: the $257 Part B annual deductible (you pay that once per year, then Plan G picks up everything else). Plan N offers the same Part B coinsurance coverage but substitutes a $20 office copay and $50 ER copay — usually at a lower monthly premium. If you rarely see specialists, Plan N may cost less annually; if you see multiple specialists regularly, Plan G's flat structure is predictable.

A critical timing note: you have guaranteed-issue Medigap rights during your 6-month Medigap Open Enrollment Period, which begins the month you turn 65 and are enrolled in Part B. During this window, insurers cannot deny you or charge more based on health. After it closes, South Dakota insurers can medical-underwrite — meaning pre-existing conditions like hypertension or diabetes can affect your eligibility or premium. That one-time window is the best — and in some cases the only — chance to lock in Plan G without underwriting.

Option 2 — Medicare Advantage PPOs: the built-in MOOP ceiling

All Medicare Advantage (Part C) plans are required by law to include a maximum out-of-pocket limit (MOOP), which caps your combined Part A and Part B in-network cost-sharing for the plan year. Once you hit the MOOP, the plan covers 100% of covered services for the rest of the calendar year. Sioux Falls offers 11 Medicare Advantage plans for 2026, including 5 standard PPOs open to any beneficiary:

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

Key considerations for Sioux Falls PPO members and Part B costs:

• The MOOP is your ceiling for in-network care. Always verify the specific plan's MOOP figure at Medicare.gov's Plan Finder before enrolling — the CMS landscape file does not publish individual MOOPs.
• The Sanford-vs-Avera network question still applies. Sanford's Align plans favor the Sanford network; out-of-network PPO use typically carries higher cost-sharing. Confirm your specific doctors are in-network for 2026.
• All plans carry the same 3.5★ CMS rating for 2026. Use the MOOP and your specific doctor and drug coverage — not star ratings alone — as the differentiation criteria.
• You still owe the Part B premium (and any IRMAA surcharge) on top of any Advantage plan premium. Two plans are $0-premium, but $0 doesn't mean $0 total cost.

Option 3 — Original Medicare only (and accepting the risk)

Some Sioux Falls beneficiaries choose Original Medicare without a Medigap supplement — deliberately or by default. This is most defensible when:

• You are very healthy, rarely see specialists, and your annual approved outpatient costs are consistently low.
• You have other retiree coverage (from an employer or union) that provides secondary benefits after Medicare pays.
• You qualify for a Medicare Savings Program (QMB) that pays your Part B cost-sharing on your behalf — the most common case for dual-eligible beneficiaries.

For beneficiaries without any secondary coverage, Original Medicare alone carries the unlimited 20% risk. The Minnehaha County chronic-condition profile — high blood pressure, diabetes, arthritis — makes that a meaningful financial exposure for many of the area's 39,532 beneficiaries. If you are considering Original Medicare alone, run your actual 2025 Part B spending first to see whether the premium savings from skipping Medigap exceed the coinsurance you would have paid.

The hospital network still matters for Part B

Part B applies to outpatient services at hospitals too — so which hospital system you use affects your Part B costs. Sioux Falls' two flagship systems carry strong CMS quality ratings, but a plan's network determines your cost structure for outpatient procedures done at each facility:

Source: CMS Hospital Compare — Overall Star Ratings.

Under Original Medicare + Medigap, you can use any provider that accepts Medicare assignment — both Sanford and Avera — at Plan G or N rates. Under Medicare Advantage, your cost-sharing at out-of-network hospitals is typically higher (though all five local PPOs have out-of-network benefits). This flexibility is one of Medigap's practical advantages for beneficiaries who want to keep access to both systems without cost-sharing uncertainty.

What to watch for 2027 and beyond

1. Part B premium and IRMAA thresholds adjust annually. CMS publishes updated figures each fall; verify before you set your budget for the following year.
2. Medigap premiums increase with age (and sometimes with carrier rate actions in South Dakota). If your Medigap premium rises materially, re-evaluate whether it still breaks even against your actual coinsurance exposure.
3. Medicare Advantage MOOP limits change year to year — always re-read the Annual Notice of Change (ANOC) each fall and check whether your plan's MOOP for the next year moved up or down.
4. Part B excess charges — the up-to-15% above Medicare rates that non-assignment providers can charge — are only covered by Plan G and Plan F. In South Dakota, most major providers accept assignment, but confirming for any new specialist or facility is a habit worth keeping.
5. The guaranteed-issue Medigap window does not come back. If you miss it at 65 and later want to switch from Advantage to Medigap, you may face medical underwriting. Plan for this decision now, not after a diagnosis.

How we know this: Big Sioux Benefits runs every article through a data desk that cross-references the CMS Parts A and B premiums fact sheet, SSA IRMAA tables, the CMS Medigap Publication 02110, the CMS PY2026 plan landscape, CMS Hospital Compare, and CDC PLACES county health data — built by Strategic AI Architects. Every number traces to a public federal dataset. This is education, not advice; confirm your specific plan costs, eligibility, and coverage with a licensed agent or Medicare.gov. We take no payment from any carrier to feature a plan.