How an anesthesia bill is calculated

Anesthesia bills confuse people for a reason that has nothing to do with the amount. The person who provided it was often a stranger who spoke with you for a few minutes, the practice is not the hospital or the surgery center, and the statement may list a code, a number of minutes and a modifier but no description you recognize. The bill has a precise structure underneath, though, and Medicare publishes every input. This guide takes the structure apart one input at a time, runs the arithmetic on examples with stated times, and then turns it into questions you can put to a billing office.

Everything in the tables below comes from CMS files checked on October 22, 2026: the Medicare Claims Processing Manual chapter on physician payment, the 2026 anesthesia conversion factor file, the CMS anesthesia base unit file, and the 2026 physician fee schedule relative value file. The dollar figures are Medicare anchors for Michigan Locality 01 (Detroit). They are not what a private insurer pays and they are not a cash price. This site covers prices only, so there is nothing here about whether anesthesia or sedation is the right choice for any procedure. That belongs between you and the clinicians.

The formula, and where each piece comes from

The Claims Processing Manual states the general rule plainly: the fee schedule amount for physician anesthesia services is based on allowable base and time units multiplied by an anesthesia conversion factor specific to the locality. Written as arithmetic:

Each piece has a different source and a different reason to exist.

Base units: a fixed value for the code

Every anesthesia code in the range 00100 to 01999 carries a base unit value that CMS publishes in a standalone file. It is meant to capture the work that does not depend on the clock, such as the evaluation before the procedure, the preparation, and the baseline difficulty of the type of procedure. A more complex procedure type has more base units. The values do not vary by locality or by how long a particular case happens to run. CMS states on its Anesthesiologists Center page that the base units are unchanged for CY 2026, and the most recent standalone base unit file it lists is the 2022 file, so the values used here come from that file.

Time units: one for each 15 minutes

Anesthesia time starts when the anesthesia practitioner begins preparing the patient for anesthesia in the operating room or an equivalent area, and ends when the practitioner is no longer furnishing anesthesia services and the patient may be placed safely under postoperative care. The practice reports the actual minutes on the claim, and the Medicare contractor divides by 15 and rounds to one decimal place. A 20-minute case is 1.3 time units, not 1 and not 2. Anesthesia time is not the same as the length of the procedure. It starts with preparation and ends at handoff to postoperative care, so the minutes on the anesthesia claim can be longer than the minutes of the procedure itself.

The conversion factor: one dollar value per unit, set by locality

CMS publishes a conversion factor for each Medicare locality, built from the national anesthesia conversion factor and adjusted by geographic practice cost indices. The 2026 national figure is $20.49754 for clinicians who are not qualifying APM participants, and $20.599835 for those who are. Locality values differ widely, as the table shows. This site's other Medicare anchors use the non-qualifying figure, so this guide does too.

Source: CMS, 2026 Anesthesia Conversion Factors (locality adjusted, updated November 20, 2025), non-qualifying APM column, checked October 22, 2026.

The spread matters for a simple reason: the same case, with the same base units and the same minutes, produces a different Medicare amount in Anchorage than in Birmingham. It is another reason that a figure copied from a website or a neighbor's bill is a weak guide to your own.

Base units for four codes

The codes below are the anesthesia codes whose CMS descriptors name procedures that appear elsewhere on this site: lower intestinal endoscopy, upper gastrointestinal endoscopy and knee arthroscopy. Which code appears on your bill is decided by the anesthesia practice from the procedure performed, so treat these as examples of how the structure works rather than as a lookup for your case.

Sources: CMS, Anesthesia base units by CPT code (2022 file; CMS states base units are unchanged for CY 2026); CMS physician fee schedule relative value file RVU26D for descriptors and status indicator J, meaning the code has no relative value units of its own and is paid by the anesthesia formula. Checked October 22, 2026.

Notice that screening colonoscopy (00812) has one fewer base unit than the general lower endoscopy code (00811). That one unit is worth $21.32 in Detroit before time is added, and it is a good example of why the code on the claim, not the name of the procedure, drives the arithmetic.

Worked example 1: a colonoscopy anesthesia claim at three durations

The table uses code 00811 (4 base units) and the Detroit factor of $21.32. The minutes are hypothetical inputs chosen to show how the time term moves the result. They are not typical durations, and they are not a statement about how long any procedure takes.

Going from 30 to 60 minutes adds two time units, which adds $42.64. In the Medicare formula, each extra 15 minutes adds exactly $21.32 in this locality, whatever the code. That is the whole sensitivity of the bill to time. Compare that with the base term: four base units are worth $85.28 before a minute is counted. For short cases, the base units are most of the amount.

If the same 30-minute case were billed as screening colonoscopy under code 00812, with 3 base units, the Medicare arithmetic gives 5.0 units and $106.60. The difference from the 00811 claim is one base unit, $21.32. Coding rules decide when a screening colonoscopy is billed as screening and when it is billed otherwise, and this guide takes no position on that coding. The point for a patient is the question to ask, covered below: which code was billed, and why.

Worked example 2: knee arthroscopy and a longer case

Code 01400 also carries 4 base units. The inputs below are again hypothetical: 90 minutes and 120 minutes of reported anesthesia time.

The base term is the same $85.28 as in the colonoscopy example, but the time term now dominates: at 90 minutes, six time units are worth $127.92, more than the base units. Anesthesia time is also not rounded to the quarter hour when it is not a multiple of 15. A case that runs 100 minutes produces 6.7 time units, which is 100 divided by 15 rounded to one decimal place.

Look at the surgeon's professional fee for the same knee arthroscopy on the knee arthroscopy price page, and the hospital outpatient payment beside it. The anesthesia amount is a third, separate layer. The site rule applies here as everywhere: professional fee, facility payment and anesthesia are separate layers, and nobody has published a total that adds them. An all-in price has to come from the facility or the practices in writing, which is what the questions to ask billing before your procedure are for.

One more input check, using a different code. An upper endoscopy anesthesia claim under 00731 has 5 base units. With a hypothetical 20 minutes of anesthesia time, the time term is 1.3 units, the total is 6.3 units, and the Medicare amount is $134.32. Rounding to one decimal place at the time-unit step, as the Medicare manual instructs, is what produces the 1.3 rather than 1.33.

Who bills, and why a medically directed claim is paid at half

An anesthesia service can be furnished by an anesthesiologist alone, by an anesthesiologist working with a certified registered nurse anesthetist or an anesthesiologist's assistant, or by a nurse anesthetist on their own, depending on the facility and the state. The Medicare manual separates the payment into three rates, and a patient who sees two anesthesia lines on a bill is usually looking at this.

• Personally performed rate. The physician performs the whole service alone, or meets the other listed conditions, and the claim recognizes the full base units plus one time unit per 15 minutes. Modifier AA reports it.
• Medically directed rate. When a physician medically directs qualified individuals in two, three or four concurrent cases and performs the listed activities (pre-anesthetic evaluation, the plan, participation in the most demanding parts, monitoring at frequent intervals, being immediately available, and postoperative care), the physician is paid 50 percent of the allowance for the service performed alone. Modifier QK reports direction of two to four concurrent procedures, and QY reports direction of one qualified nonphysician anesthetist.
• Medically supervised rate. When the physician is involved in more than four concurrent procedures, or is performing other services while directing, the contractor may allow only three base units per procedure, with possibly one added time unit for presence at induction. Modifier AD reports it.

For the 30-minute 00811 example, a medically directed physician line would be 50 percent of $127.92, which is $63.96, with the other half of the case reported by the person who performed it. The point is not that the total changes by a rule of thumb. The point is that a bill with a physician line and a nurse anesthetist line is a normal structure, and each line should carry a modifier that matches who did what.

Monitored anesthesia care, reported with modifier QS, is paid on the same basis as other anesthesia services under these rules, with the same base-plus-time arithmetic. Moderate sedation is described differently: the manual says practitioners report the appropriate CPT or HCPCS code for moderate sedation furnished in conjunction with and in support of a procedure, following CPT guidance. If a bill shows an anesthesia code for a procedure where you remember only a nurse giving a sedative, ask what was billed and by whom.

What a Medicare patient owes on an anesthesia claim

Original Medicare pays 80 percent of the approved amount after the Part B deductible, and the patient owes 20 percent, when the provider accepts assignment. The 2026 Part B deductible is $283. With the deductible already met and an approved amount of $127.92, the 20 percent share is $25.58, the 80 percent share paid by Medicare is $102.34. Providers that do not accept assignment can charge up to a limiting charge, 15 percent above the Medicare-approved amount for most services, according to Medicare.gov.

These amounts are for Original Medicare. A Medicare Advantage plan sets its own copayments and uses its own rules, and a private plan uses its own rates and cost-sharing design. A Medigap policy, which is private insurance, can cover part of the Original Medicare coinsurance, and the policy documents say which part. Check the plan documents rather than assuming.

Beyond Medicare: what you cannot read from the anchors

Most patients are not paid for by Medicare, and the honest answer is that no public source lists what a private insurer pays an anesthesia group. Private contracts commonly use their own conversion factor and may or may not use CMS base units, and the contract rates themselves are confidential in many cases. A few things you can check:

• Your insurer must give you, on request, a cost-sharing estimate through a self-service tool for covered items and services. Search by the anesthesia billing code if you know it. The guide to estimating your cost with insurance walks through what the tool must show.
• If you are uninsured, or not using insurance, CMS says providers generally must give a Good Faith Estimate when care is scheduled at least three business days ahead or when you ask, as the Good Faith Estimate guide explains.
• If the facility is in your network and the anesthesiologist is not, federal rules for insured patients generally block a balance bill. Under 45 CFR 149.420, a nonparticipating provider at a participating facility may not bill more than the in-network cost-sharing amount, and anesthesiology is on the regulation's list of ancillary services for which the notice-and-consent exception cannot be used.

That protection has limits that are worth knowing before relying on it. It applies to insured patients. It covers the visit at the facility, and it does not turn every bill into an in-network bill: your deductible and coinsurance still apply as they would in network. If a bill exceeds your in-network cost sharing, the No Surprises Help Desk at 1-800-985-3059 takes complaints.

A bill-reading table for the anesthesia line

An itemized anesthesia charge may be labeled with codes and abbreviations. This table lists the pieces you might see and what to confirm against each one.

On modifiers: the Medicare manual describes QX as a nonphysician anesthetist service with medical direction by a physician, and QZ as a CRNA service without medical direction, so a directed case shows a physician line and a QX line. Only the first four rows above are specific to anesthesia. The last two are the standard comparison from the guide to reading an explanation of benefits.

Edge cases that change the arithmetic

More than one procedure under one anesthetic

For multiple surgical procedures during one anesthetic, the Medicare manual says the practice reports the anesthesia procedure with the highest base unit value, with the multiple procedure modifier 51, and reports the total time in the line with the highest base unit value. Payment is determined from the base units of the highest-valued code plus the time units from the actual anesthesia time of all the procedures. So a second procedure adds time, not a second set of base units.

A screening that changes during the procedure

The base units for screening colonoscopy and for the general lower endoscopy code differ by one, as shown above. If a screening procedure turns into something else partway through, coding rules decide which anesthesia code applies, and different payers follow different rules. The practical step for a patient is to ask which anesthesia code was billed and whether the plan treated the service as preventive or diagnostic, because that can change the cost sharing as well as the code.

Time that is not continuous

The manual allows an anesthesia practitioner to add blocks of time around an interruption, so long as continuous anesthesia care is furnished within each block. A claim with a long gap is not automatically wrong, but the minutes should add up to the practitioner's record.

Daily hospital management codes

The manual notes that time units are not recognized for CPT code 01996, daily hospital management of epidural or subarachnoid continuous drug administration. If you see that code, the time arithmetic above does not apply to it.

How to ask about an anesthesia charge before the day

Anesthesia is easy to miss when you ask for a price, because the facility quote usually does not include it. Several questions will bring it into the open.

1. Who will provide the anesthesia, and which practice bills for it? Ask for the name of the group, not just the department.
2. Is that group in my plan's network? If you are insured, ask the plan too, since the facility's own answer may not match the plan's directory.
3. What anesthesia code do you expect to bill? The expected code gives a base unit count to work from.
4. What is your rate per unit, or your total charge for a typical case of this type? A practice that bills by units has a per-unit rate. Ask for it in writing.
5. How will you measure time? The answer should match the Medicare definition: preparation to safe handoff.
6. If I am uninsured or not using insurance, can I have a Good Faith Estimate that includes anesthesia?
7. If I have a Medicare or private plan, what does the plan estimate I will owe for the anesthesia line?

Write down the name of the person, the date, and the figures they gave. The standing instruction applies: confirm your price in writing before service. Name the exact code and setting you are confirming.

What this guide does not show

Anchors for anesthesia are only Medicare anchors. This site does not publish a self-pay range for anesthesia, because no public source met the verification rule in the procedure price method. A formula is not a price: the rate per unit in a private contract, a cash-pay practice's published charge, or a facility's bundled self-pay price can each be anywhere relative to the Medicare figure. The useful job of the Medicare formula is to give you the structure so you can read a quote line by line, spot a missing term, and ask for the one number you need.

Anesthesia bills: common questions

Where these numbers come from

• CMS, Medicare Claims Processing Manual, chapter 12, section 50, Payment for Anesthesiology Services: the general payment rule, time units, payment rates, modifiers, multiple procedures. Checked October 22, 2026.
• CMS, 2026 Anesthesia Conversion Factors, locality adjusted, updated November 20, 2025 (Detroit, Michigan Locality 01, $21.32 non-qualifying APM). Checked October 22, 2026.
• CMS, Anesthesia base units by CPT code (2022 file) and the Anesthesiologists Center, which states that base units are unchanged for CY 2026. Checked October 22, 2026.
• CMS, Physician fee schedule relative value file RVU26D: anesthesia code descriptors, status indicator J, limiting charge note. Checked October 22, 2026.
• Medicare.gov, Costs (Part B deductible $283, 20 percent coinsurance) and Does your provider accept Medicare as full payment (assignment, 15 percent limiting charge). Checked October 22, 2026.
• eCFR, 45 CFR 149.420, balance billing for non-emergency services by nonparticipating providers at participating facilities, ancillary services list. CMS, No Surprises Act consumer page, help desk number. Checked October 22, 2026.

Prices only. No diagnosis or treatment advice. Medicare anchors are not your bill, and the minutes in the examples are hypothetical. Confirm any price in writing before service.

If your anesthesia bill is part of a larger statement you cannot make sense of, take the surgeon's, facility's and anesthesia lines to the itemized-bill error check next, and match each one to a date and a person before you call anyone.