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The combined global revenue of the Big Four accounting firms reached over * billion U.S. dollars in 2025, a significant increase when compared to the previous year. The roughly **** billion U.S. dollar increase between 2024 and 2025 was notable; however, 2022 was the biggest year-on-year growth ever recorded for the Big Four, with an increase in the region of ** billion U.S. dollars when compared to 2021.

Who are the Big Four?

The four biggest accounting firms worldwide – also known as audit firms or professional services networks – are Deloitte, PwC, EY, and KPMG. The Big Four hold a dominant share of the industry, but out of the four it was Deloitte that was ranked the leading accounting firm worldwide in 2025, as they generated billion U.S. dollars in revenue. Deloitte was also ranked the leading accounting firm in the United States in 2024, with revenue figures of around ** billion U.S. dollars. 

A guide to accounting firms

The accountancy profession is part of the tertiary sector of the economy, which focuses solely on providing services to customers; being an accountant requires specialist knowledge and professional experience. There are many different disciplines to the service, ranging from simple consultancy to more complex legal issues, but the main focus is to produce detailed financial statements that determine the financial position of a company. Independent firms with strengths in the different branches of accounting have come together under a single brand name – such as Deloitte or PwC – to create professional services networks that can cost-effectively meet the needs of clients.