Ideagen Audit Analytics recently released its annual market share analysis of public company auditors as of early 2026. Here are some takeaways from the summary:

– The Big Four tighten their grip on the largest companies. The Big Four audit approximately 90% of large accelerated filers but their dominance drops sharply further down the market, where mid-tier and other firms hold the majority.

– Market share is moving and not always where you’d expect. Deloitte grew to 926 registrant clients and Baker Tilly broke into the top 10 for the first time off the back of recent merger activity.

– SPACs are back on the radar. SPACs now represent 4% of total registrants, up from 2.4% in the prior report, and the Big Four are entirely absent from the segment, leaving mid-tier and smaller firms to compete for a growing pool of engagements.

– Industry concentration reveals where auditor competition is fiercest. The Big Four audit 59% of energy and transportation companies but just 43% in trade and services.

As noted above, Deloitte continues to lead the Big 4 with a client count of 926 registrants (15% of the non-SPAC market), up from 901 in the prior year’s report. EY dropped from 869 to 799 registrants (13%), a decline of 8%. PwC was flat with 744 clients (12%), and KPMG has 639 clients (11%), up from 616 last year.

The Big 4 don’t play in the SPAC sandbox, so the lineup there looks very different, although it’s still concentrated in a handful of firms. For SPAC auditors, WithumSmith+ Brown leads the pack with 120 clients (51% market share), followed by MaloneBailey and CBIZ, each with 23 clients (10%). No other firm holds more than a 5% share of the SPAC market.

– John Jenkins