Accounting was the most boring industry in finance until it became one of the most active. In four years, private equity has bought stakes in 24 of the top 100 US CPA firms, Citrin Cooperman flipped from one sponsor to another at a $2 billion valuation, and CBIZ swallowed Marcum to become the largest pure-play public accounting firm on a US exchange. The Big 4 generate $219 billion combined and now hire AI engineers faster than auditors. KPMG just forced its own auditor to cut fees 14% because AI made the work cheaper. The talent pipeline is collapsing under a 30-year-old credentialing rule, and 45 states are racing to dismantle it. This primer walks investors through what an accounting firm actually is, how the economics work, who owns what, what AI does to fees and margins, where the regulatory risk sits, and what the sharpest hedge fund and PE questions on the sector look like.
What Is an Accounting Firm?
An accounting firm sells regulated time. Partners, managers, seniors and juniors bill hours against an engagement, and the firm collects the difference between billings, write-offs, compensation and overhead. Realisation, the ratio of fees collected to standard billing, is the single number that determines whether a partner keeps her job.
Three service lines sit under one brand at most full-service firms. Audit and assurance is the regulated core that signs off on financial statements. Tax is the recurring annuity covering compliance, advisory and structuring. Advisory is everything else, from M&A transaction services and valuations to ESG, cyber, restructuring and outsourced finance. The Big 4 derive most revenue from advisory and consulting, with audit shrinking as a share even when growing in absolute terms. Consulting accounted for the majority of Deloitte's record total in 2025, whereas EY received most of its revenue from auditing services.
Partnership economics shape everything else. Revenue per equity partner runs $500,000 to $800,000 at average firms, $1 million to $2 million at high performers, and above $2 million at Top 100 firms. Profit per partner runs $150,000 to $300,000 at small firms, $300,000 to $600,000 at well-run mid-sized firms, and $600,000 to $1 million or more at elite performers. Equity partners take home what's left after every other expense, which is why the partnership model historically resisted outside capital. There was no spare cash flow to share.
Why It Matters to Investors
Accounting is fragmentation meeting consolidation in real time. The US alone has roughly 45,000 CPA firms, the vast majority generating $1 million to $50 million in annual revenue. Demand is regulated, recurring and recession-resistant. Engagement letters renew without negotiation. Switching auditor mid-cycle triggers SEC disclosure. For a private equity sponsor, this is the textbook roll-up substrate.
The thesis has worked. Eisner Advisory Group went from $488.8 million in 2021 revenue to $848.7 million in 2023. Citrin Cooperman went from $488 million in 2022 to $700 million in 2023. Cherry Bekaert went from $293 million in 2022 to $585 million in 2023, making it the fastest-growing Top 100 firm in the country with 99.7% growth. IFAC counted fewer than 200 PE investments in accounting firms leading to roughly 900 subsequent transactions in 2025, noting that consolidation has increased four-fold since 2021.
For hedge funds, the picture is harder. The only listed pure-play is CBIZ. The Big 4 are private. But the workflow software layer is investable through Thomson Reuters, Wolters Kluwer, Intuit and Sage. The single most important question for an equity analyst is whether AI is a margin-expansion story for the incumbents or a price-compression story for the buyers. KPMG demanded audit fee reductions from its auditor due to AI-driven cost savings, achieving a 14% discount. That precedent sets the trajectory. AI savings get passed back to clients rather than kept by the auditor.
Industry Structure
The pyramid is shorter than it looks. The top four audit firms employed 1.5 million people in 2025, operate in over 150 countries each, and audit 99% of FTSE 1000 companies. Combined Big 4 revenue reached $219 billion in 2025, with Deloitte the largest, followed by EY, PwC and KPMG.
The individual numbers tell a sharper story. Deloitte's global revenue grew 4.8% in local currency to reach $70.5 billion in the fiscal year ending May 31, 2025, a rebound from 3.1% growth in fiscal 2024. PwC's global revenue grew 2.9% to $56.9 billion in fiscal 2025, marking a slowdown for the third consecutive year. The firm cut headcount by 5,600. EY Global reported 4.0% growth in local currency to $53.2 billion in revenue in the fiscal year ending June 2025. KPMG recorded 5.1% annual revenue growth in its 2025 financial year, with tax revenues up 7.5% compared to around 5.5% at EY and Deloitte and 1% at PwC. The pandemic-era double-digit growth is gone. Big 4 growth now runs 3-5%, with consulting weakest and tax strongest.
Below the Big 4 sits the global mid-market: BDO, Grant Thornton, RSM, Crowe, Baker Tilly, Mazars. Below them sits the US national tier where most of the PE action concentrates: Citrin Cooperman, EisnerAmper, Cherry Bekaert, Aprio, Wipfli, CohnReznick, Moss Adams (now merged into Baker Tilly), Marcum (now inside CBIZ). Broker Allan Koltin of Koltin Consulting Group describes PE's current focus as the "middleweights": firms with revenues between $75 million and $400 million.
Below the mid-market sit thousands of local and regional firms doing tax returns, bookkeeping, audits of private companies, and outsourced CFO work. This is the bolt-on inventory. A typical target is a $5 million to $25 million revenue firm with two retiring partners and no succession plan. EBITDA multiples for accounting firms sit around 3.0x–4.5x where EBITDA reflects market-rate partner replacement, with revenue multiples around 0.7x–1.1x and up to 1.2x–1.3x in certain local markets for sticky compliance books. Compare that to the 13x–15x mid-size financial consulting firms now command. The arbitrage is the reason PE showed up at all.
CBIZ is the lone listed US accounting pure-play. For the third quarter of 2025, CBIZ recorded strong results following the Marcum integration, which CEO Jerry Grisko called "among the most important and value-creating strategic decisions" in the company's history. CBIZ now ranks as the 7th largest accounting firm in the United States with approximately $2.8 billion in pro forma revenue, serving over 135,000 clients across 22 major markets with more than 10,000 employees.
Unit Economics
The math of an accounting firm is the math of leverage. A partner bills $500 to $1,000 an hour and earns the gap between billings, write-offs, salaries below them, and overhead. One partner sits on top of three managers, each on top of three to five seniors, each on top of two to four juniors. Each tier bills at a lower rate but generates more hours. The system works when juniors stay long enough to grow into seniors and breaks the moment they don't.
Two numbers reveal a firm's quality. Realisation is the percentage of billable work that gets paid; strong firms run above 90%. Utilisation is the percentage of available staff hours billed at all; strong firms run above 75%. A PE sponsor takes a firm at 60% utilisation and pushes it to 80% within two years. That delta is most of the EBITDA expansion in the early innings of any roll-up.
Margins vary dramatically by service line. Audit at a Big 4 firm runs low-double-digit operating margins, weighed down by regulatory cost and partner sign-off requirements. Tax compliance runs 20-30%, driven by standardisation and software. Advisory is the prize, with margins above 30% on engagements that are bespoke, premium-priced and free of audit independence restrictions.
The cost stack is brutally simple. Compensation runs 60-75% of revenue. Technology, real estate and admin together are another 10-15%. Everything else is partner distribution. This is why labour arbitrage works. A firm spending $40,000 on an offshore bookkeeper instead of $80,000 on a US equivalent doesn't just save money; it creates margin capacity to pay US staff competitively. Offshoring to India and the Philippines is now standard practice down to the mid-market.
The Private Equity Roll-Up
Understanding PE in accounting requires understanding the Alternative Practice Structure. By law, only licensed CPAs can own a firm that performs attest work. Only licensed firms can perform attest services, CPA firms must be at least majority-owned by individual licensees, and CPAs must remain responsible for attest services. Sponsors invented a workaround. The structure separates attest and non-attest entities, with CPAs serving as majority owners in the attest entity while the non-attest entity holds tax, advisory and other services and is owned by the PE fund and rolling management.
The two entities sign an Administrative Services Agreement under which the non-attest entity provides HR, IT, marketing and back-office services to the attest entity. The PE sponsor effectively owns everything except the audit licence. The mechanics involve separating non-attest assets such as tax and advisory work into a new non-CPA firm while the CPA firm retains its attest assets.
The economic logic is straightforward. Pay 8-12x EBITDA for a regional firm. Use the platform to acquire bolt-ons at 4-6x. Push synergies and margin improvement through shared services and offshoring. Sell the consolidated platform at a premium multiple. The early returns prove it works. Citrin Cooperman took investment from New Mountain Capital in April 2022 at a valuation of around $500 million. Blackstone's 2025 deal valued the firm at $2 billion, illustrating the rapid appreciation driven by PE involvement.
The first sponsor-to-sponsor flip happened in January 2025. New Mountain Capital sold Citrin Cooperman to Blackstone, representing the first top 30 CPA firm to change PE hands. A second pattern emerged in 2026. EisnerAmper's continuation vehicle brought in Carlyle AlpInvest and Hamilton Lane alongside TowerBrook, creating a "permanent capital" model that moves the firm beyond the typical five-year PE exit clock. Permanent capital matters because it solves the awkward problem of selling a partnership repeatedly to new sponsors.
The pace continues. By many industry trackers' estimates, more than 50 PE-related transactions occurred in the CPA and accounting sector through 2025, and as of early 2026 almost half of the top 30 CPA firms in the US have some form of PE investment or alternative practice structure. The Baker Tilly merger with Moss Adams, announced as a $7 billion combination, propelled the merged firm to the sixth-largest spot in the US.
The Big 4 still aren't direct targets. The audit independence rules cut off most cross-sell, the firms are too large for almost any sponsor, and the failed EY split showed how brutal a Big 4 partnership vote becomes when real money is at stake.
The Big 4 and the Failed Split
EY's Project Everest is the most expensive lesson in Big 4 history. In 2022 and 2023, Ernst & Young pursued the most ambitious restructuring attempt in modern Big Four history: a plan, code-named Project Everest, to separate most of its consulting business from its audit and assurance business. The logic was clean. Audit independence rules prevent the firm from selling consulting to its audit clients. A separately listed consulting firm could sell freely, command tech-multiples on IPO, and let audit partners cash out.
It collapsed. The plan collapsed in April 2023 after more than a year of work, heavy internal conflict, and very substantial expense. Reporting from the Financial Times and Wall Street Journal indicates that the project consumed roughly $600 million and involved tens of thousands of hours of partner and staff effort. The proximate cause was a fight over how to split the tax practice and what compensation audit partners would receive. The deeper cause was the partnership model itself. EY's US boss Julie Boland raised concerns about protecting the audit business and profit targets for consulting, and partners increasingly questioned whether the consulting business would emerge too burdened by debt.
EY took on $700 million of debt to cover the costs of a deal that never happened. The episode killed appetite for similar splits at the other Big 4. PwC, Deloitte and KPMG have all chosen instead to internally bulkhead consulting and audit, hire AI engineers aggressively, and grow advisory while leaving audit as the lead-generation tip of the spear. According to Financial Times analysis of more than 50,000 job listings, AI-related roles made up almost 7 per cent of postings across the Big Four last year, while audit roles accounted for under 3 per cent.
The Big 4 cannot exit audit even when consulting is more profitable. Audit remains the gateway into major corporate relationships. It gives firms recurring access to executives, boards and finance teams that later buy consulting, compliance and transformation services. Audit is loss-leader infrastructure for the cross-sell. The moment one of the four exits, the remaining three take the relationships.
Audit Quality and the PCAOB
Audit quality matters because it dictates fee pricing power, regulatory scrutiny and litigation risk. The PCAOB inspects the largest firms annually and publishes deficiency rates. The 2024 cycle showed broad improvement. The aggregate Part I.A deficiency rate for the Big Four US firms, which collectively audit approximately 80% of the market capitalization of public companies, decreased to 20% in 2024 from 26% in 2023. Aggregate deficiency rates at NAF triennially inspected firms decreased from 67% in 2023 to 61% in 2024.
The dispersion across the Big 4 is wider than the headline suggests. Deloitte's inspection results were the best in the GNF group, followed closely by PwC, with deficiencies in 14% of Deloitte audits and 16% of PwC audits. At the other end of the spectrum, BDO had a 60% deficiency rate, down from 86% in 2023. Deloitte and PwC have both experienced slowly rising deficiency rates since 2020, while KPMG, which had the highest deficiency rates among the Big Four between 2014 and 2021, has been steadily improving since 2018. EY's deficiency rate jumped from 16.9% in 2020 to 42.9% in 2022, declining to 37.8% in 2023, and the uptick led EY to disengage from 84 audit clients.
The 2025 inspection cycle is trending better still. PCAOB Acting Chair George Botic said in September 2025 that preliminary results show a decrease in Part I.A deficiency rates from 2024, suggesting that the efforts by these firms during the past few years are positively impacting audit quality.
The investor relevance is twofold. PE-backed firms that take on attest work inherit the PCAOB inspection regime. A bad inspection report damages the platform's reputation and feeds the narrative that sponsor-driven cost cuts compromise audit quality. The reverse is also true. If a firm rebuilds audit quality post-acquisition, fee pricing power increases and litigation exposure declines.
The Talent Crisis and the 150-Hour Rule
The accountant pipeline is collapsing. According to the US Bureau of Labor Statistics, more than 300,000 professionals have exited the field since 2020, shrinking the workforce by over 17%. Nearly three-quarters of CPAs are at or near retirement age. The number of people sitting for the CPA exam has declined by more than 30% since 2016. Finance roles requiring CPA credentials now take 73 days to fill, 41% longer than comparable positions.
The proximate cause is the 150-hour rule. Most states require 150 semester hours of education to become a CPA, 30 hours more than a standard bachelor's degree. This typically means a 5th year of college or a master's degree, adding $15,000 to $50,000 in education costs. Compare that to finance, tech and consulting, where a four-year degree is sufficient and starting salaries are higher. A first-year audit associate at a mid-size firm makes $55,000-$70,000 in most markets, a first-year financial analyst at a tech company makes $75,000-$95,000, and a first-year software engineer makes $90,000-$130,000.
States are unwinding the rule. Ohio made the first move in 2025 to abolish the 150-hour rule and offer alternative pathways to CPA licensure, taking effect in 2026. About 45 states have passed or introduced new CPA licensing laws or rules, in a bid to lower barriers and tackle the accounting shortage. The most common alternative is a bachelor's degree plus two years of supervised experience plus the CPA exam. The fix arrives late and isn't enough on its own. The pipeline impact won't show up in hiring data until 2028-2030.
For PE-backed firms, the talent crisis is the entire investment thesis stress test. The roll-up assumes you can keep the people. The reality is that the consolidators paying highest have the most synergies to fund the pay, which makes them talent magnets and the independent local firms talent donors. This dynamic also explains why the offshoring shift to India and the Philippines has accelerated.
AI and the Audit Margin Question
The single most important question in accounting today is whether AI is a margin-expansion story or a fee-compression story. The honest answer is that nobody knows yet. The early evidence leans toward fee compression at the high end and margin expansion at the mid-market.
The high-end signal is the KPMG-Grant Thornton episode. KPMG threatened to drop its auditor, Grant Thornton, if it didn't pass along savings from the use of AI tools, ultimately achieving a 14% discount. That is one of the largest professional services buyers in the world telling the auditor to share AI productivity gains. If it becomes precedent, audit pricing at the public-company end of the market compresses meaningfully even as costs fall. The Big 4 keep some margin but lose more in fees.
The productivity gains are real. Firms have reported audit fieldwork time reductions of 20-30% with AI, resulting in less disruption for clients and a lower cost of service. Deloitte uses AI to read all lease agreements in advance. EY embeds AI across tax and consulting. PwC reports 20-50% productivity gains in code writing and data analysis. KPMG built a Trusted AI framework.
The mid-market signal is different. PE-backed platforms have far more to gain from AI because they're consolidating fragmented firms with legacy workflows. Standardise the tech stack, apply AI across compliance work, and the EBITDA expansion is mechanical. The buyers of mid-market accounting services are also less sophisticated negotiators than the FTSE 100, so fee compression takes longer to arrive.
The structural play is the workflow software layer. Wolters Kluwer secures a 58.92% market share in tax software, with Thomson Reuters' UltraTax CS holding 2.53%. The tax software market is projected at $28.88 billion in 2026, growing at 11.82% CAGR to $50.5 billion by 2031.
A medium-term scenario worth modelling: AI shrinks audit headcount by 30-40% across the Big 4 within five years while fees decline by 10-15%. Operating margin would expand on those numbers. The bigger second-order question is whether the audit-to-consulting cross-sell still works when audit teams are half as large and rarely on-site.
The Regulatory and Independence Problem
Audit independence is the boundary nobody can cross. Generally, with the combination of an attest firm and a non-attest entity, the non-attest entity and the entities it controls should be independent of financial statement audit and review clients of the attest firm. A PE-backed CPA firm cannot audit any portfolio company of its sponsor. A Big 4 firm cannot consult for an audit client on most material engagements. The cross-sell every firm relies on operates within a regulatory perimeter that is easy to breach by accident.
The regulators are watching. In APS and PE-backed environments, attest practices must retain exclusive authority over client acceptance, engagement performance and conclusions, partner evaluation and compensation related to attest work, and quality control and risk management. NASBA, the AICPA's PEEC committee, the SEC and the PCAOB are all reviewing how the alternative practice structure works in practice. A task force is examining whether the attest firm and nonattest entity are network firms because they cooperate for the purpose of enhancing the firms' capabilities to provide professional services and share characteristics like common brand name or significant professional resources.
If the regulators conclude that the two entities are a single network, the independence rules apply to both. That would limit the non-attest entity's ability to serve audit clients of its sister attest firm. The thesis stress test is existential.
The other regulatory risk is fee transparency. IFAC explored the potential consequences, both good and bad, of the global consolidation spree. Possible risks include higher fees for clients and more investments in advisory services over audit and assurance services. If consolidation produces measurable price increases for audit clients, expect congressional and SEC interest.
The Workflow Technology Layer
The accounting firm is a technology buyer as much as a service provider. Three players dominate the practice management and tax software stack. The global tax technology market is led by Wolters Kluwer, with its CCH Axcess Tax platforms offering integrated tax compliance, workflow automation, and real-time regulatory updates. Thomson Reuters runs ONESOURCE for corporates and UltraTax CS for firms. Intuit owns the small-business and consumer end with QuickBooks, Lacerte and ProConnect.
These are not competitive markets in any meaningful sense. Switching costs are extraordinary for an accounting firm. Migrating practice management software involves moving years of client files, billing history, workflow templates, document repositories and tax preparation data. Most firms switch once a decade if ever.
The AI overlay is where the competition happens. Wolters Kluwer integrated its GenAI-powered CCH AnswerConnect into CCH iFirm and completed the acquisition of Isabel Group's European accountancy portfolio. Thomson Reuters introduced ONESOURCE AI, a large-language-model assistant that drafts memos, classifies transactions and generates audit documentation.
For an equity analyst, the workflow tech layer is the cleanest way to play the accounting industry. Recurring revenue, high switching costs, sticky users, AI-driven feature expansion, and direct exposure to professional services consolidation. Mid-market PE platforms standardise on one or two vendors as they roll up, which produces share gains for the chosen vendor. Watch which workflow vendors the largest PE-backed platforms standardise on. That's where the share concentration plays out.
Primary Research Questions
The right Woozle expert call depends on what the investor is trying to answer.
For an investor underwriting a PE-backed CPA platform, the questions are partner retention, fee realisation under integration, organic versus acquisition growth, audit independence breaches, regulatory exposure under the APS structure, AI adoption pace, and the realistic margin ceiling. Ask former partners of acquired firms how compensation changed post-deal, what fraction of the partner group has rolled equity, how client retention has held up after integration, and what the realistic five-year revenue trajectory looks like once acquisition growth slows.
For a hedge fund analyst with a position in CBIZ or considering one, the questions are Marcum integration synergies versus original plan, churn in legacy Marcum clients, organic same-unit growth, leverage trajectory, sensitivity to audit fee pressure, and whether the PE-backed roll-ups eventually IPO and crowd CBIZ's positioning.
For an analyst with a position in Thomson Reuters, Wolters Kluwer, Intuit or Sage, the questions are share-of-wallet in the PE-backed platforms, AI feature adoption rates, the threat from new entrants, churn versus the legacy installed base, and pricing power as AI productivity gains accrue.
For an analyst short the Big 4 cross-sell thesis or modelling fee compression, the questions are how often KPMG-style fee renegotiations occur, what proportion of audit work AI now performs, the headcount trajectory in audit divisions, the audit-to-consulting conversion rate, and how partners are responding to declining audit profitability.
The experts worth speaking to include current and former Big 4 audit partners, former audit committee chairs of public companies, ex-PE-backed CPA platform partners, M&A brokers serving the accounting industry, NASBA and state board officials, AI strategy leaders at the Big 4, CFOs who recently switched audit providers, mid-market firm CEOs, and partners at firms that rejected PE offers and chose to stay independent.
The non-obvious experts are the ones who run the workflow tech vendor sales teams. They see which platforms are winning at which firms, which features the PE-backed buyers prioritise, and what the average tenure of a switching cycle now looks like in a sector with this much M&A.
Current Debates Worth Watching
Six debates are live. Does the PE consolidation thesis still work at current entry multiples now that Citrin Cooperman has traded at 4x its 2021 valuation in four years? Do the alternative practice structures survive a serious SEC or PCAOB review of network independence? Does AI fee compression hit the mid-market before the EBITDA synergies arrive? Can the talent pipeline recover fast enough to support a workforce that needs to grow? What happens when the first PE-backed firm has a serious audit quality failure under sponsor ownership?
The sixth debate is the newest. Permanent capital structures like EisnerAmper's continuation vehicle change the exit math for sponsors. If permanent capital wins, the IPO path for accounting platforms may never open. If it doesn't, the next 24 months produce a wave of sponsor-to-sponsor flips that test market appetite at progressively higher valuations.
How Woozle Helps
Woozle Research runs primary research programmes on accounting and CPA firms for hedge funds, private equity sponsors and sell-side research desks. We source former Big 4 audit partners, partners of PE-backed mid-market firms, audit committee chairs, NASBA officials, PCAOB inspectors and workflow technology sales executives. We design and run expert call programmes, survey panels of finance leaders on auditor switching, and bespoke channel checks on the PE-backed platforms.
If you are diligencing an accounting industry investment, evaluating a workflow tech position, or building a thesis on AI-driven audit fee compression, get in touch.
