2026 Anesthesia Billing Units & Concurrency Modifier Calculator
Compare Medicare Part B 0.1-decimal 15-minute time units against commercial payer conversion factors, ASA physical status units (P3–P5), and concurrency splits.
CY 2026 CMS vs. Commercial Anesthesia Unit Formula Reference
Medicare Part B computes time units as Minutes ÷ 15 rounded to one decimal place, excludes ASA physical status (P3–P5) and qualifying circumstance codes (99100–99140), and applies the CY 2026 national anesthesia conversion factor of $20.4976 ($20.5998 for qualifying APM practitioners).
AA vs QK / QX / QY / QZ: what the concurrency split does to this case
| Modifier | Who performed / directed | Share of the computed allowed amount |
|---|---|---|
| AA | Anesthesiologist personally performed | 100% |
| QZ | CRNA without medical direction | 100% allowed basis (payer rules vary) |
| QK | Physician directing 2-4 concurrent cases | 50% |
| QX | CRNA under medical direction | 50% |
| QY | Physician directing 1 CRNA | 50% |
Run the same case under AA and then under QK/QX above: the unit count does not change, the payable halves. That split, not the time math, is where most anesthesia estimate disputes start.
KX modifier threshold: have you crossed $2,480 this year?
For CY 2026 the KX threshold is $2,480 for PT and SLP combined and $2,480 separately for OT (CMS Therapy Services CY 2026 update; re-confirmed at each November re-check). Crossing it is not a cap and not permission: append KX only on claims where continued therapy is medically necessary and the record documents it. The year-to-date fields in the allocator above run this check on every calculation.
Frequently Asked Billing Questions
Does Medicare pay extra units for P3 or P4 physical status modifiers?
No. Medicare excludes physical status modifying units, whereas most commercial contracts add +1 unit for P3, +2 for P4, and +3 for P5.
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