What Are the Big 4 Accounting Firms?
By Markets & Investing DeskUpdated Nov 10, 2026
Definition
The Big 4 are Deloitte, PwC, EY and KPMG, the four largest professional services networks, best known for auditing nearly every large US public company.
Key takeaways
- Each brand is a network of legally separate national member firms under a central coordinating entity.
- The Big 4 held 99.7% of the S&P 500 audit market in 2022, with PwC leading at a 35.7% share.
- Arthur Andersen collapsed in 2002 over Enron documents, which turned the Big Five into the Big Four.
- The Sarbanes-Oxley Act of 2002 created the PCAOB and restricted non-audit services sold to audit clients.
The Big 4 are the four largest professional services networks in the world: Deloitte, PwC (PricewaterhouseCoopers), EY (Ernst & Young) and KPMG (Klynveld Peat Marwick Goerdeler). They are known first as accounting and audit firms, because together they audit the financial statements of nearly every large public company in the United States. Their work also extends to tax, consulting, risk, deal advisory and legal services.
The Four Firms Compared
| Firm | FY2025 revenue (USD) | Employees | Countries and territories | Global headquarters |
|---|---|---|---|---|
| Deloitte | $70.5 billion | 470,000+ | 150+ | London, U.K. |
| PwC | $56.9 billion | 364,000+ | 137 | London, U.K. |
| EY | $53.2 billion | About 393,000 | 150+ | London, U.K. |
| KPMG | $39.8 billion | 276,000+ | About 140 | Amstelveen, Netherlands |
How the Big 4 Firms Are Structured
“Deloitte” or “KPMG” on a building does not mean a single global corporation. Each brand is a network of national member firms that are legally separate partnerships or companies. A central coordinating entity sets standards, manages the brand and shares methods and technology.
This affects clients and investors. The U.S. member firm that signs an American company’s audit opinion is the entity that is responsible for that opinion and is overseen by U.S. regulators. Each brand’s reported “global revenue” is the combined total of its member firms.
What Services Do the Big 4 Provide?
- Audit and assurance: independent examination of a company’s income statement, balance sheet and cash flows, ending in a formal audit opinion.
- Tax: compliance, planning, transfer pricing and interpretation of tax law for corporations and wealthy individuals.
- Consulting: strategy, management, technology and cybersecurity projects.
- Financial advisory: mergers and acquisitions, valuation, corporate restructuring and forensic accounting.
- Risk and legal advisory: regulatory compliance, internal controls and, in some countries, legal services.
Why the Big 4 Matter
Public companies must have their annual financial statements audited, and investors rely on that audit when they read reported revenue, profits and assets. Almost all of that work at the largest companies goes to four firms. The Big 4 accounted for 99.7% of the S&P 500 audit market in 2022, and PwC led with a 35.7% share. In 2025, they audited every company in the Fortune 500. That concentration means a significant error or failure at one firm affects many issuers at once.
History: From the Big Eight to the Big 4
In the 1980s, the industry was dominated by eight U.S. or U.K. based firms: Arthur Andersen, Arthur Young, Coopers & Lybrand, Deloitte Haskins & Sells, Ernst & Whinney, Peat Marwick Mitchell, Price Waterhouse and Touche Ross.
The consolidation unfolded in three steps:
- 1989: Arthur Young combined with Ernst & Whinney to form Ernst & Young. Deloitte Haskins & Sells merged with Touche Ross to form Deloitte & Touche.
- 1998: Price Waterhouse and Coopers & Lybrand merged to form PricewaterhouseCoopers, which left five firms.
- 2002: Arthur Andersen collapsed after it was found to have shredded documents related to Enron’s falsified accounts. The Big Five became the Big Four.
The Enron scandal also led to the Sarbanes-Oxley Act of 2002 in the United States. The law created the Public Company Accounting Oversight Board (PCAOB) to inspect auditors of public companies. It also restricted many non-audit services that a firm may sell to a company it audits.
Example: Reading the Auditor Line
Hypothetical example. An investor reviewing a mid-size U.S. listed manufacturer finds the “Report of Independent Registered Public Accounting Firm” near the front of its annual report. It is signed by the U.S. member firm of one of the Big 4 and gives an unqualified (clean) opinion. That tells the investor three things:
- A large, PCAOB-inspected firm tested the statements.
- The firm concluded the statements are fairly presented under U.S. GAAP.
- Any material weaknesses in internal controls would have been disclosed.
It does not tell the investor that the business is a good investment or that fraud is impossible. If the company later switches to a smaller auditor, analysts usually look at the stated reason for the change.
Limitations and Criticisms
- Concentration: With four firms auditing almost all large companies, clients have little choice. A conflict of interest with one firm can leave only two or three options.
- Independence concerns: The firms sell consulting and tax work alongside audits. Rules limit what they can sell to audit clients, but the commercial tension remains a recurring regulatory topic.
- No guarantee: An audit gives reasonable assurance, not certainty. Andersen was among the most reputable firms of its time before Enron.
- Workload: Busy season usually runs from January to April, when year-end audits and tax filings are due, with further peaks around quarterly reporting. Employees can work about double their off-season hours during these periods.
What the Big 4 Are Not
- Not the “Big Three” consultancies: McKinsey, Boston Consulting Group and Bain are pure strategy consultancies and do not perform statutory audits.
- Not the only accounting firms: Mid-tier networks such as Grant Thornton and BDO audit many public and private companies, mostly smaller ones.
FAQs
What does "Big 4 audit experience" mean?
It means the person worked in the audit or assurance practice of Deloitte, PwC, EY or KPMG. Employers read it as training in large-company audits, standardized methods and heavy deadline workloads, which is why it is often a requirement for corporate controller and finance roles.
What is the difference between an accountant and a CPA at a Big 4 firm?
An accountant generally holds an accounting degree. A Certified Public Accountant has also passed the CPA exam and met state education and experience requirements for a license. Only licensed CPAs can sign audit opinions in the U.S., so promotion in Big 4 audit practices typically depends on earning the license.
The Bottom Line
Investors reading annual reports and companies choosing auditors deal with the Big 4 because these firms check the numbers behind nearly every large public company. A clean opinion from one of them shows the statements were tested and fairly presented under U.S. GAAP, yet it offers reasonable assurance only. It says nothing about investment quality, and the firms' concentration means a failure at one can affect many companies.
