Big Four

The Big Four refers to the four largest professional services and accounting firms in the world: Deloitte, PricewaterhouseCoopers (PwC), Ernst & Young (EY), and KPMG. Together, these big four accounting firms audit the majority of publicly traded companies and provide tax, consulting, and advisory services to businesses of all sizes.

If your company works with external auditors, tax advisors, or management consultants, there's a good chance you're dealing with one of the Big Four.

What are the Big Four?

The big 4 are global professional services networks that dominate the accounting and advisory industry. Deloitte and EY each operate in over 150 countries, PwC operates in around 150, and KPMG operates in over 138 countries. Each firm employs hundreds of thousands of people and generates tens of billions in annual revenue.

While they started as accounting and bookkeeping↗ practices, the big four companies now offer a wide range of services, from cybersecurity consulting to deal advisory. Despite this expansion, audit and assurance work remains at the core of what makes these firms unique. They are the only firms with the scale and regulatory approval to audit most of the world's largest companies.

In the UK alone, the Big Four audit the vast majority of FTSE 100 companies and hold around 98% of FTSE 350 audit fees.

The Big Four firms at a glance

Here is a quick comparison of the big 4 firms. Ranked by revenue, Deloitte leads, followed by PwC, EY, and KPMG.

• Deloitte — London, UK | ~$70.5 billion revenue (FY 2025) | ~470,000 employees | Founded 1845
• PwC — London, UK | ~$56.9 billion revenue (FY 2025) | ~364,000 employees | Founded 1849/1998 (merger)
• EY — London, UK | ~$53.2 billion revenue (FY 2025) | ~393,000 employees | Founded 1849/1989 (merger)
• KPMG — Amstelveen, NL | ~$39.8 billion revenue (FY 2025) | ~276,000 employees | Founded 1987 (merger)

All four firms are structured as networks of independent member firms, meaning each country's practice operates as a separate legal entity under a shared brand and standards.

What services do the Big Four offer?

The big four consulting firms and their service lines go well beyond traditional accounting. Here is what they typically offer:

Audit and assurance

This is the foundation of the Big Four's reputation. The big four audit firms examine financial statements to confirm they are accurate and comply with standards like IFRS↗ or GAAP↗. For many large and publicly listed companies, a Big Four audit is either required by regulators or expected by investors.

Tax advisory

Each firm has a dedicated tax practice that helps businesses with compliance, planning, and cross-border tax structuring. This includes VAT↗ advisory, transfer pricing, and tax-efficient supply chain design.

Consulting and advisory

Management consulting has become one of the fastest-growing areas for the Big Four. Services range from digital transformation and strategy to technology implementation and organisational change. In fact, consulting now accounts for a significant share of revenue at Deloitte and PwC.

Risk and financial advisory

This covers areas like internal audit, regulatory compliance, KYC↗, anti-money laundering, forensic investigations, and transaction advisory (mergers and acquisitions). For finance teams, this is often where the Big Four get involved during due diligence processes or regulatory reviews.

History of the Big Four

The Big Four were not always four. The industry went through several waves of consolidation:

• The Big Eight (pre-1989): Eight major firms dominated the market, including Arthur Andersen, Coopers & Lybrand, and Price Waterhouse. In 1987, Peat Marwick merged with KMG to form KPMG.
• The Big Six (1989): Two mergers reduced the group to six. Ernst & Whinney merged with Arthur Young to form EY, and Deloitte merged with Touche Ross.
• The Big Five (1998): Price Waterhouse and Coopers & Lybrand merged to create PwC, bringing the count down to the big 5 accounting firms.
• The Big Four (2002): Arthur Andersen collapsed following the Enron scandal. Its clients and staff were absorbed by the remaining four firms.

Since 2002, no firm has come close to matching the scale of the Big Four, making this group remarkably stable.

Why the Big Four Matter for businesses

Even if your company is not a multinational corporation, the Big Four likely affect your operations in some way. Here is why they matter for finance teams and business owners:

• Audit requirements: If your business is growing, preparing for investment, or approaching a public listing, you may need a Big Four audit to satisfy regulators or investors.
• Tax complexity: Operating across borders, managing VAT↗, or restructuring your business often requires the kind of specialist tax advice these firms provide.
• Compliance and risk: Regulatory requirements around financial reporting, KYC↗, and anti-fraud controls are areas where Big Four advisory teams are frequently engaged.
• Benchmarking: Big Four publications, surveys, and industry reports are widely used by CFO↗s and finance leaders to benchmark performance and stay current on trends.

The Big Four have also faced scrutiny over audit quality and conflicts of interest, with regulators in the UK and elsewhere pushing for reforms to increase accountability. For businesses, this means paying attention to how audit standards and oversight continue to evolve.