The 10 Best OON Billing & NSA Arbitration Companies in 2026

The short version

• Ten options ranked: The Auctus Group, HaloMD, CollectionPro, Gottlieb & Greenspan, Callagy Law, Cohen Howard, Millennium Medical Billing, the hospital-side complex-claims firms, your current billing company’s “OON support,” and filing IDR yourself.
• Providers won roughly 85% of federal IDR disputes in 2024. The money is not lost in arbitration; it is lost before arbitration, in the underpayments nobody catches and the disputes nobody files inside the 4-business-day window.
• The field splits into finders and filers. Pure-play IDR shops and law firms argue disputes you bring them. A billing company sees every EOB, so it catches the underpayment and files. One firm on this list is specialty-focused, does the billing, and runs the arbitration in-house.

The 10 best out-of-network billing and NSA arbitration companies in 2026

Two disclosures before the rankings. First: we run the first company on the list, so discount our placement on sight and read the matrix instead. Second: two of the law firms ranked here, Gottlieb & Greenspan and Callagy Law, are firms we partner with on shared clients, and we love working with both. We are ranking them anyway, because leaving out firms this good to protect a ranking would tell you everything about the ranking.

Here is the number the whole field stands on. Providers won roughly 85 percent of federal IDR disputes in 2024, and about 85 percent of determinations came in above the qualifying payment amount. The payer’s first number loses six times out of seven when someone shows up to argue. The catch is the showing up: the money is lost in the underpayments nobody catches and the filings nobody makes, not at the arbitration table.

That is why the matrix asks the question no other ranking prints: who handles the full revenue cycle, including IDR? Pure-play IDR shops and law firms are filers; they work what you bring them. A billing operation sees every EOB, so it is the only structure that catches what you did not know to bring.

1. The Auctus Group: the specialty billing firm that finds and files

We are a surgical-specialty RCM firm, plastics, dermatology, and ENT, that runs No Surprises Act arbitration in-house as part of the billing operation. That structure is the whole pitch, so we will state it plainly. Because we do the billing, we post every payment against the expected rate, which means the underpaid flap reconstruction gets flagged the day the EOB lands, inside the open-negotiation and 4-business-day IDR windows, not at quarter-end when someone finally reviews the aging. That expected-rate engine is our Billing IQ platform. Finding is the half of this work the pure-plays cannot do for you.

The specialty part is not decoration. An IDR brief is a clinical argument: why this reconstruction, at this complexity, with these operative findings, merits more than the payer’s benchmark. We write those briefs from the same specialty knowledge that codes the cases, with ProCode AI, our in-house engine, turning operative reports into the CPT record the brief stands on. Generally speaking, the argument wins on the chart, and the chart is our home field.

Best fit: surgical practices with a real OON book, plastics and reconstruction above all, that want the underpayments found, negotiated, and arbitrated inside one accountable operation. If you only need a one-time stack of old disputes argued, a pure-play or a law firm below may be the lighter tool.

2. HaloMD: the pure-play IDR machine

HaloMD does one thing, IDR, for thousands of providers nationally, with a proprietary platform and what they describe as AI-driven insights on dispute strategy. Volume like that buys real pattern knowledge: which arguments land with which IDR entities, where payers default, how offers move. If arbitration were a sport, this is a team that plays every day.

The structural limit is the intake. HaloMD argues the disputes that reach it; nothing in a pure-play model watches your remits to find what should have been disputed. Pair one with a billing operation that actually flags underpayments, or accept that your filing list is only as good as whoever builds it.

Best fit: groups with high dispute volume and an internal team that already identifies underpayments reliably.

3. CollectionPro: the boutique that fronts the fees

CollectionPro is a New York pure-play, 100 percent IDR by their own description, with more than 10,000 out-of-network arbitrations filed and plastic surgery case studies on the site. Two things earn the ranking: pricing that starts around 10 percent and only bills on wins, and their practice of advancing arbitration fees, up to $1,200 a case, so the practice fronts nothing. That fee structure removes the exact excuse most practices use for not filing.

Same intake limit as every pure-play: you bring the disputes.

Best fit: practices that know they are underpaid, want aligned economics, and hate fronting fees.

4. Gottlieb & Greenspan: the NSA law firm we work with

Full disclosure, stated straight: we partner with Gottlieb & Greenspan on shared clients, and we love working with them. They are a healthcare reimbursement law firm that works NSA arbitration, state-governed IDR, and state and federal litigation, which is the complete escalation ladder in one shop. That last rung matters: when a payer ignores an IDR award, and payers do, a billing company writes letters while a law firm files suit.

Best fit: practices with contested, high-dollar OON claims that may need the litigation path, and anyone whose payer has stopped honoring awards.

5. Callagy Law: the medical revenue recovery heavyweight

Same disclosure, same warmth: we partner with Callagy on clients and love what they do. Callagy Law has recovered roughly $450 million for medical providers across a practice that spans healthcare arbitration, PIP and no-fault, workers’ compensation, and ERISA litigation, with more than 100 professionals across New Jersey, New York, and Arizona. That breadth is the differentiator: underpayment fights that cross into ERISA plans or comp carriers need a firm that lives in those statutes, and most of this list does not.

Best fit: providers with complex, multi-statute recovery problems, ERISA plans, comp carriers, no-fault, on top of standard OON underpayment.

6. Cohen Howard: the surgeons’ OON firm

Cohen Howard is a reimbursement law firm built specifically around out-of-network surgical claims, plastic and reconstructive surgery first among them, with over $150 million recovered on a contingency model and a team that includes billers and coders, not just attorneys. Their claim-stage flexibility, from pre-authorization through appeal through litigation, fits how surgical OON disputes actually unfold.

Best fit: OON surgeons, especially plastics and reconstruction, with high-dollar contested claims and no billing-side arbitration bench.

7. Millennium Medical Billing: the generalist billco with an arbitration desk

Millennium is a New Jersey full-service billing company with an NSA arbitration service line and a claimed 90 percent dispute success rate. They are proof that the finds-and-files structure exists outside our shop, and credit for building it. Their listed specialties run spine, orthopedics, and pain management; plastic surgery is not on the list, so surgical-specialty practices should ask the case-mix question hard.

Best fit: ortho, spine, and pain practices that want billing and disputes under one roof.

8. The hospital-side complex-claims firms

Aspirion and the firms like it run out-of-network and NSA recovery at health-system scale, with real technology and real results, for hospitals. A private surgical practice is not their customer, and the operating model, built for facility claims and enterprise contracts, does not shrink gracefully. If you are a facility, interview them. If you are a practice, this is the wrong aisle.

Best fit: hospitals and health systems, which is the point.

9. Your current billing company’s “OON support”

Most billing companies will tell you they handle out-of-network. Ask what that means operationally and the answer is usually: they post the payer’s payment. The allowed amount comes in at a number nobody would defend, it gets posted, adjusted, and closed, and the practice eats the difference as a contractual write-off that was never contractual. No negotiation, no filing, no calendar watching the 4-day window. At an 85 percent provider win rate, a billing company that never files is not neutral; it is donating your margin to the payer, one EOB at a time.

The test costs one question: how many IDR disputes did you file for practices like mine last year, and what did you recover? A real number ends the conversation one way. The word “process” ends it the other.

Best fit: nobody, at least not on the OON book. Keep the billco if the in-network work is good; just stop calling what happens to your OON claims “support.”

10. Filing it yourself

The federal IDR portal is open to providers, and a practice administrator can genuinely run a dispute end to end: open negotiation, initiation, the brief, the offer. For a practice with two or three disputes a year and an administrator who likes a fight, self-filing is real and the economics are unbeatable.

The model breaks on calendar math. Open negotiation runs 30 business days; the IDR window opens for 4 business days after that. Miss it and the claim is done, permanently. At two disputes a year the deadlines are manageable. At two a week they are a job, and the person doing that job next to their actual job will start missing windows precisely when the OON book grows, which is precisely when the money got big.

Best fit: small OON books, occasional disputes, and an administrator with appetite. Graduate to a professional the month the volume stops being occasional.

How NSA IDR works in 2026, and where the money actually leaks

The mechanics in one breath: the No Surprises Act covers emergency care and out-of-network care at in-network facilities; when the payer’s initial payment disappoints, you have 30 business days of open negotiation, then 4 business days to initiate federal IDR; the arbitration is baseball-style, each side submits one number and a certified IDR entity picks one, no splitting. The qualifying payment amount, the payer’s median in-network rate, anchors the argument, and your brief’s job is to prove why this case merits more.

One distinction buyers mix up constantly: the certified IDR entities, the FHASes and iMPROve Healths of the world, are the referees. You do not hire them; they decide. Everyone ranked on this page is a player, someone who argues to the referee on your behalf. A vendor that describes itself as an IDR entity is telling you it works for the process, not for you.

And 2026 moved the goalposts toward filing. The federal IDR Operations final rule took effect August 3, 2026: the administrative fee dropped from $115 to $15 per party (in effect for disputes initiated since June 11), the batching cap doubles from 25 to 50 line items for negotiations opening on or after November 1, and payers must now attach standardized claim-adjustment codes and identifying information to initial payments, which makes underpayments easier to spot and disputes cheaper to run. Every excuse in the do-not-file column got smaller this year. The $100 that used to gatekeep a marginal dispute now buys lunch.

Now the leak. That 85 percent provider win rate comes with a growing asterisk: through 2024, third-party filing specialists climbed from 13 to 22 percent of the top initiating parties. The sophisticated OON providers are industrializing their filing. The rest are subsidizing them, because every unfiled dispute leaves the payer’s number standing by default, and the payer prices its first offers knowing exactly what fraction of providers never push back. Generally speaking, an OON practice that has never filed an IDR dispute does not have a clean book. It has an unaudited one.

The audit is mechanical, which makes it delegable. Every OON EOB compares against two numbers, the QPA and your historical allowed amounts, and the gaps are the dispute pipeline. That work belongs wherever your payments post, which is the argument for treating arbitration as a billing-channel function rather than a standalone purchase, and it is why the second column from the right in the matrix above has so few names in it.

Six questions that sort NSA arbitration companies fast

Run these on every vendor on this page, including us, and get the answers in writing.

1. “Who identifies the underpayments, you or me?” The load-bearing question. Filers work your list; finders build it. If the answer is your list, price in the cost of building it, because that cost is a salary.
2. “How many disputes did you file last year, and what was your win rate against the 85 percent federal baseline?” The public baseline is the calibration: a vendor winning 85 percent is performing at average, whatever the brochure says. Ask it exactly that way.
3. “What do you charge, who fronts the arbitration fees, and what happens on a loss?” Contingency from roughly 10 percent, fee-advancing, win-only billing, and hourly all exist on this page. Losses have fees attached; know whose.
4. “What happens when the payer ignores the award?” Awards are binding and payers still slow-walk them. A billing firm escalates; a law firm litigates. Know which rung your vendor can reach before you need the rung.
5. “Show me a brief for my specialty.” An IDR brief for a flap reconstruction is a clinical document. A vendor whose sample briefs are all emergency medicine is learning your specialty on your money.
6. “Do you watch my deadlines or do I?” Thirty business days of negotiation, then 4 to file. Somebody’s calendar owns those windows, and if the contract does not say whose, it is yours.

We ran the same exercise on the billing side in our dermatology billing rankings, and the pattern holds here: the vendors worth hiring answer fast, in writing, with numbers. The rest answer with process.

Frequently asked questions

This article describes how billing arrangements, credentialing timelines, and vendor pricing generally work — it is not legal, tax, or financial advice. Credentialing clocks, contract terms, fee structures, and what counts as “collections” vary by payer, state, and vendor. Wage figures cited are national BLS medians and will differ in your market. Confirm the specifics with your own counsel and with the vendors you are evaluating before you sign anything.