Big Four hold onto their share of SEC market

After losing market share for public company audits in 2024, the Big Four accounting firms held steady in 2025, accounting for just over half (51%), according to a new report.

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Overall, the distribution of Securities and Exchange Commission audit clients held steady in 2025, with the 10 largest auditors handling 65% of audits, and the rest going to smaller firms, according to Ideagen Audit Analytics’ annual “Who Audits Public Companies” report.

Deloitte held onto the top spot, which it took up in 2024, with 926 SEC registrant clients in 2025, and 15% of the market. Ernst & Young dropped a percentage point but held onto second place, with 799 clients and 13%, while PwC held steady in third with 744 clients and 12% of the market, and KPMG grew its share to 11%, with 639 clients.

Two firms joined the Top 10 public company audits, both thanks to major mergers: CBIZ CPAs, which combined with Marcum in 2024, and Baker Tilly, which merged with Moss Adams in 2025.

Beyond the Top 10, a total of 219 other firms handle the remaining 35% of SEC registrant audits — a breakdown that stayed the same.

All of these market shares exclude the market for special purpose acquisition company audits, which are overwhelmingly handled by mid-tier and smaller firms, and only made up 4% of the overall market in 2025 in any case.

That 4%, however, represents a jump from 2024, when SPACs were 2.4% of the market. There were 236 SPAC registrants last year, against 6,050 non-SPAC registrants. That’s 86 more SPACs than in 2024, but 235 fewer traditional public companies, down from 6,285.

The Ideagen Audit Analytics report covers a number of other aspects of the audit market, including auditor breakdowns by:

• Filer status, including non-accelerated filers (52%), accelerated filers (12%) and large accelerated filers (33%);
• Exchange (NASDAQ, the New York Stock Exchange, and over the counter);
• Jurisdiction (U.S. and foreign);
• Region of the U.S.; and,
• Industry.

The report is available online here.
(Read more: “Mega-mergers drive new SEC audit clients in 2025.”)