Medicare Anesthesia Conversion Factor Lookup by Locality

The formula, in CMS’s own words

Medicare Claims Processing Manual, chapter 12 section 50.A: the fee schedule amount “is, with the exceptions noted, based on allowable base and time units multiplied by an anesthesia conversion factor specific to that locality.” Section 50.G sets the time unit: divide reported anesthesia minutes by 15 and round to one decimal place, and recognise no time units at all for CPT 01996.

The base units are not supplied here. CMS communicates them to its contractors through the annually released HCPCS file, and its newest published base-unit file is from 2022 and is derived from the American Society of Anesthesiologists with no licence stated. Chapter 12 states no rounding rule for the resulting amount, so none is applied to it.

Conversion factors by locality

The table lists the 2026 January (annual release under the CY2026 final rule) factors for the localities in seven states that injury bills most often come from. The full set covers 109 localities from $19.42 to $28.15. A state is not a single figure: New York carries several localities and California carries 29, so the locality on the claim decides the number, not the state. Both 2026 columns are shown because CMS publishes both, but only the non-qualifying figure is used to price.

Source: ANES2026.txt inside rvu26a-updated-12-29-2025.zip, the 2026 January (annual release under the CY2026 final rule) set, in force Jan 1, 2026 onward. Locality names from cms-pfs-data-2026-01.json. A state with more than four localities is truncated here; the CMS file named above carries all 109.

Why the date of service decides the factor

Because two of the six changes in this archive land in the middle of a year. On Mar 9, 2024, every one of the 109 localities moved when the CY2024 conversion factor was revised and CMS reposted the January files: Alabama went from $19.45 to $19.77, so 8 March 2024 and 9 March 2024 are different numbers. On Oct 1, 2023, CMS corrected exactly 2 of the 112 localities then in force, Puerto Rico and Virgin Islands, from $21.12 to $21.13 and changed nothing else. Each set is what CMS published for its own span. An earlier figure is never quietly overwritten, so a report priced from the January file still traces to the January file.

6 distinct sets across 17 archived Physician Fee Schedule releases: two releases whose factors are identical do not ship two copies of numbers that must never disagree. For 2023 and 2024 the factor file inside CMS’s physician release names no national figure, so it is read from CMS’s separate locality-adjusted anesthesia conversion factor file for that year. Its locality factors match these, apart from the two (Puerto Rico and the Virgin Islands) that CMS corrected in October 2023. The locality count is not stable either: 112 in the oldest set carried here and 109 in the newest.

The anesthesia payment modifiers

Each definition below is CMS’s own wording, with the chapter 12 section it comes from. Where the manual states a share of the allowance, it is given. Where it states none, none is given, and that is not an omission: working out a percentage CMS has not published is exactly the kind of figure that does not survive being asked where it came from.

AA · 100 percent of the allowance

Anesthesia Services performed personally by the anesthesiologist. ch. 12 Sec. 50.I, amount from Sec. 50.B. Sec. 50.B: the A/B MAC "must determine the fee schedule payment, recognizing the base unit for the anesthesia code and one time unit per 15 minutes of anesthesia time" where "the physician personally performed the entire anesthesia service alone", which is the allowance itself with no reduction.

QY · 50 percent of the allowance

Medical direction of one qualified nonphysician anesthetist by an anesthesiologist. ch. 12 Sec. 50.I, amount from Sec. 140.4.2. Sec. 140.4.2: for a single medically directed case "the payment amount for the service of each is 50 percent of the allowance otherwise recognized had the service been furnished by the anesthesiologist alone".

QK · 50 percent of the allowance

Medical direction of two, three or four concurrent anesthesia procedures involving qualified individuals. ch. 12 Sec. 50.I, amount from Sec. 50.C. Sec. 50.C: the A/B MAC "determines payment at the medically directed rate for the physician on the basis of 50 percent of the allowance for the service performed by the physician alone".

QX · 50 percent of the allowance

Qualified nonphysician anesthetist service: With medical direction by a physician. ch. 12 Sec. 140.3.3, amount from Sec. 140.4.2. Sec. 140.4.2, the other half of the same sentence as QY: each of the two is paid 50 percent of the allowance otherwise recognized.

QZ · 100 percent of the allowance

CRNA service: Without medical direction by a physician. ch. 12 Sec. 140.3.3, amount from Sec. 140.3. Sec. 140.3: the fee schedule for a qualified nonphysician anesthetist "is the applicable locality-adjusted anesthesia conversion factor multiplied by the sum of allowable base and time units"; only the medically directed rate is "a fixed percentage", and a CRNA not paid at that rate "may not exceed the allowance for a service personally performed by a physician".

AD · no share stated in chapter 12

Medical Supervision by a physician; more than 4 concurrent anesthesia procedures. ch. 12 Sec. 50.I, units from Sec. 50.D. Sec. 50.D changes the UNITS rather than taking a share: the A/B MAC "may allow only three base units per procedure when the anesthesiologist is involved in furnishing more than four procedures concurrently... An additional time unit may be recognized if the physician can document he or she was present at induction."

QS · no share stated in chapter 12

Monitored anesthesia care service. ch. 12 Sec. 50.I and Sec. 140.3.3. Sec. 50.I: "The QS modifier can be used by a physician or a qualified nonphysician anesthetist and is for informational purposes." It changes no amount.

How bill reviewers use the conversion factor

Medical billing experts use it to rebuild the Medicare allowance for an anesthesia line and set it beside the billed charge. The workflow is to read the anesthesia code, the reported minutes, the modifier and the locality off the claim, take the base units from the CMS HCPCS file the practice already licenses, compute the time units under chapter 12 section 50.G, multiply by the locality factor in force on the date of service, and apply the share chapter 12 states for the modifier. Every one of those inputs is shown, so the arithmetic is document review rather than assertion. For the professional and facility codes on the same bill, use the Medicare rate lookup. For New Jersey no-fault claims, the state schedule is in the NJ PIP fee schedule lookup. For the full workflow from a stack of bills to a signed report, see Desk.