Mega-mergers drive new SEC audit clients in 2025

Two billion-dollar firms — CBIZ CPAs and Baker Tilly — pulled in by far the most new Securities and Exchange Commission audit clients in 2025, thanks to two different mega-mergers.

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CBIZ CPAs topped the charts with a whopping 168 new engagements and a net of 154, with 152 of its new clients coming in through its addition of billion-dollar firm Marcum in late 2024. (See “Net engagement leaders.”)

M&A also gave a major boost to Baker Tilly, which came in second for the year, with 71 new clients and a net of 66. The vast majority of its new engagements — 63 out of 71, came from its combination with West Coast powerhouse Moss Adams. (See “2025 total client gains & losses.“)

Taken together, the two combinations caused a massive spike in new engagements in the second quarter of 2025 — but they weren’t the only mergers that made waves.

Pennsylvania-based Stephano Slack, for instance, added 10 new clients (out of a total of 13) from its acquisition of the public company book of business of Florida-based Assurance Dimensions, which exited the public company auditing market in the spring of 2025, but continues to provide other audit services. And five of Top 100 Firm Withum’s 17 new engagements came from its August acquisition of a fellow Top 100 Firm, New York-based Freed Maxick.

Meanwhile, one of the other big winners for the year, Nigeria-based LAO Professionals, got a major boost from Olayinka Oyebola & Co.’s. agreeing to be suspended from SEC practice for six years for its alleged role in a massive securities fraud. Fifteen of LAO’s 19 new clients came from Olayinka Oyebola.

Clients by filing status, and more

In terms of clients by filing status, Deloitte led among new large accelerated filers, followed closely by KPMG, while Baker Tilly took the lead among accelerated filers and small reporting companies. CBIZ had a commanding position in terms of new non-accelerated filers and small reporting companies. (See “Audit leaders.“)

By and large, the Big Four dominated the league tables for new market capitalization and new assets audited, as well as new audit fees, thanks to the larger size of their individual clients. (See “New client leaders.“)

KPMG topped the list for new market cap audited, with Lam Research Corp., a provider of wafer fabrication equipment to the semiconductor industry, contributing by far the largest chunk of $123.8 billion; none of the firm’s other new clients added more than $20 billion in new market cap. KPMG also came first in terms of new audit fees, with contributions more or less evenly distributed across its clients.

PricewaterhouseCoopers came first in new assets audited, with sizable contributions from a number of investment funds and trusts.

Deloitte & Touche came second in new market cap and new assets, with medical device manufacturer Dexcom Inc. standing out for its $30.6 billion in new market cap, and Washington Mutual Investors Fund for its $175.7 billion in new assets.

Finally, CBIZ CPAs came in second for new audit fees, with contributions spread fairly evenly across its mass of new clients.

Data for the quarterly rankings are provided by Ideagen Audit Analytics, a premium online intelligence service delivering audit, regulatory and disclosure analysis. Reach them at (508) 476-7007, info@auditanalytics.com or www.auditanalytics.com.