TLDR
A CRNA's anesthesia services are billed using a formula: (base units + time units) × conversion factor. The conversion factor determines what the case pays, and it varies by payer. Medicare pays $20.50 per unit in 2026. Commercial insurance pays a national average of $82.43 per unit. Medicaid pays roughly 85% of the Medicare rate. A one-hour knee arthroscopy bills 8 total units, which means $164 from Medicare, $660 from commercial, or $139 from Medicaid for the same work by the same provider in the same OR. The care model matters too: a CRNA practicing independently bills 100% of the allowed rate, while a CRNA under medical direction bills 50%.
Anesthesia billing uses a unit-based formula: (base units + time units) × conversion factor per unit. Medicare pays $20.50 per unit in 2026 (CMS). Commercial insurers pay a national average of $82.43 per unit (ASA, 2025 survey). Medicaid averages roughly 85% of the Medicare rate. The same one-hour surgery generates $164 from Medicare, $660 from a commercial payer, or $139 from Medicaid.
A CRNA in a four-room ambulatory surgery center outside Nashville finishes her third case of the morning. A screening colonoscopy, 28 minutes of anesthesia time. She charts the start and stop times, enters the anesthesia code, and moves to the next room. The billing department will process that case as 5 base units plus 1.87 time units (28 minutes divided by 15), totaling 6.87 units. If the patient carries commercial insurance, the case generates roughly $566. If the patient is on Medicare, it generates $141. Same CRNA. Same 28 minutes. Same level of care. The payer determines the revenue.
That gap between $566 and $141 is the single most important number in anesthesia economics, and most CRNAs never see it. Understanding how billing works changes how you evaluate offers, negotiate rates, and think about which facilities are financially stable enough to keep paying you.
The Billing Formula: How Anesthesia Revenue Gets Calculated
Every anesthesia case is billed using three components: base units, time units, and a conversion factor.
Base units are fixed values assigned by CMS to each anesthesia CPT code. They reflect the complexity and risk of providing anesthesia for a specific procedure. A screening colonoscopy carries 5 base units. A knee arthroscopy carries 4. A cesarean section carries 7. A total hip replacement carries 8. A cardiac surgery with bypass carries 15 to 25. The base units do not change based on time, patient condition, or provider type. They are the same whether a physician anesthesiologist or a CRNA performs the case.
Time units represent the duration of continuous anesthesia care, calculated as total anesthesia minutes divided by 15. A 45-minute case generates 3 time units. A 90-minute case generates 6. Medicare does not round: 47 minutes equals 3.13 time units, not 3 or 4. Time starts when the provider begins preparing the patient for anesthesia and ends when the patient is safely transferred to post-anesthesia care.
The conversion factor is the dollar amount per unit that the payer reimburses. This is where the math diverges.
What Each Payer Pays Per Unit
Medicare's 2026 national anesthesia conversion factor is $20.50 per unit (CMS, CY 2026 Physician Fee Schedule). This number has declined in real terms over the past decade. In 2019, the Medicare CF was $22.27. By 2023, it had dropped to $21.12. The 2026 figure of $20.50 represents a modest recovery from the 2025 low of $20.32, but it remains below 2019 levels when adjusted for inflation.
Commercial insurance pays a national average of $82.43 per unit (ASA Commercial Conversion Factor Survey, 2025), with a national median of $76.00. The commercial rate is approximately four times the Medicare rate. This ratio varies by geography and insurer. Some commercial contracts pay as high as $120 per unit in high-cost metro areas. Others pay as low as $55 in markets with aggressive managed care penetration.
Medicaid pays approximately 85% of the Medicare rate, or roughly $17 per unit nationally. Medicaid rates vary by state more than any other payer. Some states pay at or near Medicare rates. Others pay 60% or less. Rural facilities with high Medicaid patient populations face the sharpest revenue constraints because their anesthesia cases generate the lowest per-unit reimbursement.
What Common Procedures Actually Bill
The math gets concrete fast. Here are five procedures a CRNA encounters regularly, with billing at each payer level:
Screening colonoscopy (CPT 00812, 5 base units, ~30 min = 2 time units, 7 total units):
Medicare: 7 × $20.50 = $144
Commercial: 7 × $82.43 = $577
Medicaid: 7 × $17.43 = $122
Knee arthroscopy (CPT 01382, 4 base units, ~60 min = 4 time units, 8 total units):
Medicare: 8 × $20.50 = $164
Commercial: 8 × $82.43 = $659
Medicaid: 8 × $17.43 = $139
Cesarean section (CPT 01961, 7 base units, ~60 min = 4 time units, 11 total units):
Medicare: 11 × $20.50 = $226
Commercial: 11 × $82.43 = $907
Medicaid: 11 × $17.43 = $192
Total hip replacement (CPT 01214, 8 base units, ~90 min = 6 time units, 14 total units):
Medicare: 14 × $20.50 = $287
Commercial: 14 × $82.43 = $1,154
Medicaid: 14 × $17.43 = $244
Cardiac surgery with bypass (CPT 00567, 20 base units, ~240 min = 16 time units, 36 total units):
Medicare: 36 × $20.50 = $738
Commercial: 36 × $82.43 = $2,967
Medicaid: 36 × $17.43 = $627
The pattern is clear. A CRNA providing anesthesia for a commercial-insurance hip replacement generates seven times more revenue than the same case on Medicaid. The work is identical. The skill is identical. The risk is identical. The revenue is not.
How the Care Model Changes What Gets Billed
The billing formula stays the same across care models. What changes is who bills and what percentage each provider receives.
CRNA Independent Practice (Modifier QZ). A CRNA practicing without medical direction bills 100% of the allowed rate under the QZ modifier. In 31 states with full practice authority, this is the standard model. The CRNA handles the entire case, bills the full (base + time) × conversion factor, and there is no physician split. For a commercial knee arthroscopy, that is $659 going to one provider.
Medical Direction / Care Team (Modifiers QK + QX). In the care-team model, an anesthesiologist medically directs two to four CRNAs simultaneously. The anesthesiologist bills with the QK modifier. Each CRNA bills with the QX modifier. Each provider receives 50% of the allowed amount. For the same commercial knee arthroscopy, the anesthesiologist receives $330 and the CRNA receives $330. The facility generates the same total revenue, but it supports two provider salaries from it.
Physician Personally Performed (Modifier AA). An anesthesiologist performing the case alone bills 100% under the AA modifier. No CRNA is involved. The facility pays one provider for one case in one room. This is the least efficient model for high-volume facilities because it locks one anesthesiologist into one OR.
Supervision (Modifier QY). An anesthesiologist supervising a single CRNA. Each bills 50%. This 1:1 ratio is less efficient than medical direction (1:2 through 1:4) and is typically used when an anesthesiologist is only overseeing one concurrent case.
The economic logic of each model is straightforward. Independent CRNA practice generates the highest per-provider revenue: one provider, 100% of the billing. Medical direction generates the highest facility throughput: one anesthesiologist enabling four simultaneous ORs. The choice between models depends on state practice authority, surgical volume, and whether the facility can recruit enough providers for either approach.
The 85% Rule: What Is Changing
UnitedHealthcare reduced CRNA reimbursement for independently performed services (QZ modifier) by 15% effective October 2025 (Becker's ASC). The change caps CRNA payment at 85% of the physician rate, aligning with existing Medicare and Medicaid standards. The cut applies in most states except Arkansas, California, Colorado, Hawaii, Massachusetts, New Hampshire, and Wyoming.
The practical impact: a commercial knee arthroscopy that previously billed $659 under the QZ modifier on a UHC plan now bills $560 after the 15% reduction. Over a full year for a CRNA performing 1,500 cases, the cumulative reduction reaches $100,000 or more depending on payer mix.
The AANA has opposed the change, arguing that CRNAs provide the same anesthesia services as physician anesthesiologists and the reimbursement reduction devalues equivalent care. The industry is watching whether other major commercial payers follow UHC's lead. If the 85% cap becomes standard across commercial insurance, it will reshape the economics of independent CRNA practice and strengthen the financial case for care-team models where the total billing remains at 100%.
Why This Matters for Your Next Job Offer
A CRNA evaluating two job offers at $225 per hour should ask what the facility's payer mix looks like. A high-commercial-mix ASC generates $500 to $1,000 per case in anesthesia revenue. A Medicaid-heavy safety-net hospital generates $120 to $250. The facility paying $225 per hour from commercial revenue has margin to sustain that rate. The facility paying $225 per hour from Medicaid revenue is subsidizing your salary from somewhere else, often a stipend.
The salary variation across states reflects these payer dynamics. States with higher commercial insurance penetration and lower Medicaid populations tend to pay CRNAs more because the per-case revenue supports it. States with high Medicaid populations and low commercial mix pay less or rely on stipends to close the gap.
Related resources: What is a CRNA stipend?, Inside the compensation report, CRNA locum rates in 2026, Texas CRNA salary data, The case for CRNA independence.
See CRNA rates across all 50 states on RxRooster. Every rate visible before the first call.
Frequently Asked Questions
How much does a CRNA bill per case?
Anesthesia billing per case depends on procedure complexity, case duration, and payer. A one-hour knee arthroscopy (8 total units) generates $164 from Medicare, $659 from commercial insurance, or $139 from Medicaid. A cesarean section (11 units) generates $226 from Medicare or $907 from commercial insurance. The formula is (base units + time units) × the payer's conversion factor per unit.
What is the Medicare anesthesia conversion factor in 2026?
The 2026 Medicare anesthesia conversion factor is $20.50 per unit nationally (CMS Physician Fee Schedule). This represents a modest increase from the 2025 rate of $20.32 but remains below the 2019 level of $22.27. Medicare conversion factors vary slightly by payment locality. APM-eligible participants receive a slightly higher rate of $20.60 per unit.
How much does commercial insurance pay for anesthesia compared to Medicare?
Commercial insurance pays approximately four times the Medicare rate for anesthesia. The 2025 national average commercial conversion factor is $82.43 per unit (ASA survey), compared to Medicare's $20.50. The commercial median is $76.00. Rates range from $55 per unit in aggressive managed-care markets to $120 or more in high-cost metro areas.
What is the difference between QZ and QX modifiers for CRNA billing?
QZ indicates a CRNA performed the anesthesia service independently without medical direction, billing 100% of the allowed rate. QX indicates a CRNA performed under the medical direction of an anesthesiologist, billing 50% of the allowed rate (the anesthesiologist bills the other 50% using the QK modifier). The total facility revenue is the same, but the QZ model concentrates 100% in one provider while the QK/QX model splits it between two.
How does the UnitedHealthcare CRNA reimbursement cut affect billing?
Effective October 2025, UnitedHealthcare reduced CRNA reimbursement for independently performed services (QZ modifier) by 15%, capping payment at 85% of the physician rate. A commercial knee arthroscopy that previously billed $659 on a UHC plan now bills approximately $560. The AANA opposes the change. The cut does not apply in Arkansas, California, Colorado, Hawaii, Massachusetts, New Hampshire, and Wyoming.