Federal law has protected patients from most surprise medical bills since January 2022, and the single largest remaining exception is the ground ambulance. The No Surprises Act covers emergency services, out-of-network providers working inside in-network facilities, and air ambulance transport. It does not cover the ambulance that drives you to the hospital. The Centers for Medicare and Medicaid Services states the exclusion directly in its consumer guidance, adding only that other remedies may be available.
That single gap accounts for a large share of the surprise bills people still receive, and understanding where the law’s boundary sits is the difference between a bill you can contest and one you cannot.
What the law covers
Three categories are protected.
Emergency services. Plans that cover emergency care must cover it even at an out-of-network emergency facility, and they are prohibited from requiring prior authorization. Coverage extends to post-stabilization care. Whether a situation counts as an emergency is judged by a prudent layperson standard, meaning it turns on what a reasonable person would have believed at the time rather than on the final diagnosis.
Out-of-network providers at in-network facilities. This addresses the classic case: a patient does everything right, confirms the hospital is in network, and then receives a separate bill from an anesthesiologist, radiologist or pathologist who is not. For non-emergency services the protection applies at a defined set of facilities, specifically a hospital, a hospital outpatient department, a critical access hospital or an ambulatory surgical center.
Air ambulance. Both helicopter and fixed-wing medical transport by out-of-network providers are covered, and cost sharing cannot exceed the in-network requirement. CMS notes the protections may apply even when the pickup point is outside the United States.
What the law does not cover
Ground ambulance is the headline exclusion, and the numbers explain why it matters. The Peterson-KFF Health System Tracker, analyzing large-employer claims data, found that 51 percent of emergency ground ambulance rides and 39 percent of non-emergency rides included an out-of-network charge. The same analysis estimated that ambulances bring roughly 3 million privately insured people to an emergency room each year, and that as many as 1.5 million of them may face a surprise bill.
The ownership structure explains part of the problem. That analysis found 62 percent of emergency ground ambulance rides are provided by government-based organizations, with fire departments accounting for 37 percent and other government entities 25 percent. Private non-hospital operators handled 30 percent. A service delivered largely by municipal agencies sits outside a federal billing framework built around commercial insurance networks.
Other exclusions apply. Non-emergency care at an out-of-network facility is not covered, nor is care at an in-network setting outside the four facility types listed above, which leaves some clinics and physician offices outside the framework. Items and services a plan does not cover at all remain uncovered. Enrollees in Medicare, Medicare Advantage, Medicaid, CHIP, TRICARE, the Indian Health Service and Veterans Affairs fall under their own protections rather than this law.
The good faith estimate
A second protection applies to people without insurance or choosing not to use it. Providers and facilities must give these patients a written good faith estimate of expected charges.
The timing is specified. If a service is scheduled at least three business days in advance, the estimate is due within one business day of scheduling. If it is scheduled at least ten business days ahead, or requested without being scheduled, the estimate is due within three business days. The document must list the items and services, applicable diagnosis codes, expected service codes and expected charges per provider or facility.
A good faith estimate is not a bill. It is a prediction, and the law attaches consequences to a prediction that turns out wrong.
A worked example: the $400 rule
If the final bill exceeds the good faith estimate by at least $400, the patient can initiate patient-provider dispute resolution.
The detail that trips people up is that eligibility is determined separately for each provider or facility listed on the estimate, not on the total across all of them. Suppose an estimate lists a facility fee of $2,000, a surgeon at $1,500 and an anesthesiologist at $700. The bills arrive at $2,300, $1,750 and $1,050. The total overage is $900, which sounds like it clears the threshold. It does not. Each line is $300, $250 and $350 over its own estimate, and no single provider crossed $400. Nothing here is eligible.
The deadline is 120 calendar days from receiving the initial bill. A selected dispute resolution entity requests information from the provider within ten business days and must decide no later than 30 business days after receiving it. The determination has to be the estimate amount, the billed amount, or something in between.
Two provisions do real work here. While a dispute is pending, the provider must not move the bill to collections or threaten to, must stop existing collection efforts, must suspend late fees and must not retaliate. And for an item that never appeared on the estimate at all, with no credible justification offered, the amount owed is set to zero.
An administrative fee applies to the process. CMS has stated the fee may change from year to year, so the current figure should be checked against current CMS material rather than assumed from older guidance.
The consent exception
Patients can waive these protections, which is where the framework gets thin. A provider may seek written consent to balance bill, but only for post-stabilization services and for non-emergency services that are not ancillary.
Four conditions must all hold for the non-emergency waiver: the services are not ancillary, they are not furnished as a result of unforeseen urgent medical needs arising at the time of service, another in-network provider could deliver them, and the provider complies with applicable state law. Providers must use the standard CMS or state notice and consent documents, present them separately from other paperwork, and supply a good faith estimate of expected charges before any waiver takes effect. CMS notes that a patient who needs medical transport to travel is not in a condition to receive notice or give consent.
How often the system gets used
The volume is far larger than anyone projected. CMS reported that 1,372,563 disputes were initiated in the second half of 2025 alone, up 16 percent from the first half. Cumulatively, from the program’s launch in April 2022 through July 2026, CMS recorded 7,048,593 disputes initiated and 6,527,388 closed.
Outcomes have been lopsided. In the second half of 2025, providers, facilities and air ambulance providers prevailed in about 85 percent of payment determinations, and the prevailing offer exceeded the qualifying payment amount in roughly 87 percent of cases. Emergency department services accounted for 52 percent of determinations and radiology 15 percent. Filing is also concentrated: CMS found the three most active initiating parties accounted for about 44 percent of all disputes initiated in the first half of 2025, and the top ten for about 69 percent.
One frequently repeated claim deserves correction. Early in the program a large majority of filings were found ineligible, roughly 69 percent in the first half of 2022. By 2025 that had fallen to between 17 and 19 percent. The statement that most dispute filings get thrown out was true three years ago and is not true now.
Where this leaves patients
The No Surprises Act removed a real category of financial harm, and the dispute volume shows the underlying billing conflicts were larger than the pre-2022 debate assumed. The ambulance exclusion remains, and it is the one most likely to reach someone during the worst hour of their life. Congress directed the agencies to convene an advisory committee on ground ambulance and patient billing, which is where any fix would begin.
Organizations working on household affordability, including the nonpartisan grassroots 501(c)(3) Fight For A Living Wage, count unpredictable medical costs among the pressures that make a full-time wage insufficient. Surprise billing is a narrow slice of that, but it is a slice where the law already moved once and could move again.