Research

The Audit Fees and Auditor Market Report 2026

By The Ledgerism Editorial Team · The Ledgerism Brief Editorial Team produces original, methodology-disclosed accounting and tax research—data trackers, databases, and reference guides built to be the most-cited source in the field. Every figure is verified against primary sources including FASB, the IRS, the PCAOB, NASBA, the AICPA, and state boards of accountancy.

A definitive, source-linked profile of what U.S. public companies pay their external auditors, how those fees have moved over two decades, and how concentrated the auditor market is. Every figure below carries its exact year, geography, and source. Where the core industry dataset sits behind a paywall, only figures published in free summaries, press releases, or regulatory/press citations are used, and they are labeled Tier-2.

A note on the primary data source

Granular U.S. public-company audit-fee data is compiled almost entirely by one commercial vendor, Ideagen Audit Analytics (IAA, formerly Audit Analytics), from SEC proxy-statement and annual-report fee disclosures. The full year-by-year datasets and the underlying fee tables are PAYWALLED. This report uses only the figures IAA and its licensees have published in free reports, press releases, blog posts, and figures cited by the press. Those figures are classified Tier-2 (credible market research derived from primary SEC filings). Government sources (GAO, PCAOB) and the UK FRC are Tier-1 but address market structure and concentration more than aggregate fee levels. Readers needing engagement-level fee data should consult the underlying SEC filings (Tier-1) or license the IAA dataset directly.

Executive summary

• U.S. SEC registrants paid a total of $21.675 billion in fees to their external auditors in FY2024, a 1.4 percent increase over FY2023 despite a roughly 7 percent decline in the registrant population (Ideagen Audit Analytics, Sept 2025).
• The average SEC registrant paid $3.26 million in total auditor fees in FY2024, an all-time high and a 9 percent increase over FY2023 (Ideagen Audit Analytics, Sept 2025).
• The average audit-fee component alone reached $2.726 million in FY2024, up 8 percent from $2.516 million in FY2023 (Ideagen Audit Analytics, Sept 2025).
• Average audit fees have risen from $681,000 in FY2003 to $2.726 million in FY2024, roughly a 4x increase over 21 years (Ideagen Audit Analytics, 2023 report and Sept 2025).
• Big Four firms (PwC, EY, Deloitte, KPMG) received 69.5 percent of all SEC-registrant audit-fee payments in FY2024, with more than 250 other firms sharing the remaining 30.5 percent (Ideagen Audit Analytics, Sept 2025).
• The GAO found the Big Four audited over 78 percent of U.S. public companies and 99 percent of all public-company sales in 2003, and in 2006 the overall public-company audit market had a Herfindahl-Hirschman Index of 2,300, well above the 1,800 “highly concentrated” threshold (GAO-03-864, 2003; GAO-08-163, 2008).
• Audit fees per $1 million of revenue fell to $612 in FY2024 from $619 in FY2023, showing fees have not kept pace with revenue growth even as absolute fees hit records (Ideagen Audit Analytics, Sept 2025).
• For context, the UK Big Four earned 98 percent of FTSE 350 audit fees in 2023 and 2024, a more concentrated fee share than the US SEC-registrant market (Financial Reporting Council, Dec 2024 update).

Key findings

• U.S. SEC registrants paid $21.675 billion in total auditor fees in FY2024, up 1.4 percent from FY2023 (Ideagen Audit Analytics, Sept 2025).
• The average SEC registrant paid $3.26 million in total auditor fees in FY2024, a record and a 9 percent year-over-year rise (Ideagen Audit Analytics, Sept 2025).
• The average audit-fee component was $2.726 million per registrant in FY2024, up 8 percent from $2.516 million in FY2023 (Ideagen Audit Analytics, Sept 2025).
• Average non-audit service fees rose 14 percent to $530,000 per registrant in FY2024 (Ideagen Audit Analytics, Sept 2025).
• Large accelerated filers paid an average of $6.06 million in audit fees in FY2024, versus $1.62 million for accelerated filers and $734,000 for non-accelerated filers (Ideagen Audit Analytics, Sept 2025).
• Finance was the highest-fee sector at an average $4.055 million and Manufacturing second at $3.386 million in FY2024 (Ideagen Audit Analytics, Sept 2025).
• Audit fees averaged $612 per $1 million of revenue in FY2024, down from $619 in FY2023 (Ideagen Audit Analytics, Sept 2025).
• The average audit fee was $681,000 in FY2003, rising to $2.243 million in FY2022 and $2.726 million in FY2024 (Ideagen Audit Analytics, 2023 report and Sept 2025).
• Big Four firms received 69.5 percent of all SEC-registrant audit-fee payments in FY2024 (Ideagen Audit Analytics, Sept 2025).
• Within the S&P 500, the Big Four earned 99.7 percent of audit fees in FY2022, with PwC alone at 35.7 percent (Ideagen Audit Analytics, FY2022 S&P 500 analysis).
• The average S&P 500 company paid $10.78 million in audit fees in FY2022, a record and a 3 percent increase over FY2021 (Ideagen Audit Analytics, FY2022).
• The GAO reported the Big Four audited over 78 percent of U.S. public companies and 99 percent of public-company sales in 2003 (GAO-03-864, July 2003).
• The public-company audit market had a Herfindahl-Hirschman Index of 2,300 in 2006, and 82 percent of Fortune 1000 companies saw their auditor choice as limited to three or fewer firms in 2008 (GAO-08-163, 2008).
• There were 1,544 PCAOB-registered firms at the end of 2024, falling about 6 percent to 1,444 by the end of 2025 (PCAOB, 2024 Annual Report; Accounting Today, 2025).
• The UK Big Four earned 98 percent of FTSE 350 audit fees in 2023 and 2024, and total PIE-market audit fees reached GBP 1.4 billion in 2023, up 27 percent over 2022 (Financial Reporting Council, Dec 2024 update).

Section 1: Total and average U.S. public-company audit fees

U.S. public-company audit fees are disclosed in proxy statements and annual reports under SEC rules, then aggregated by Ideagen Audit Analytics. The most recent full-year analysis covers FY2024 and reflects 6,656 companies.

• Total auditor fees paid by SEC registrants were $21.675 billion in FY2024 (Ideagen Audit Analytics, Sept 2025).
• Total fees rose 1.4 percent over FY2023 even though the SEC registrant population fell about 7 percent (Ideagen Audit Analytics, Sept 2025).
• Average total auditor fees per registrant were $3.26 million in FY2024, a 9 percent increase and an all-time high (Ideagen Audit Analytics, Sept 2025).
• The audit-fee component averaged $2.726 million per registrant in FY2024, up 8 percent from $2.516 million in FY2023 (Ideagen Audit Analytics, Sept 2025).
• Non-audit service fees averaged $530,000 per registrant in FY2024, up 14 percent (Ideagen Audit Analytics, Sept 2025).
• In FY2022, total fees for all SEC registrants were about $20.2 billion, of which audit fees were $16.8 billion (Ideagen Audit Analytics, 2023 report).

What the numbers mean: absolute fees keep setting records mainly because the fee charged per company rises faster than the number of companies falls. The registrant count dropping while total fees still rise indicates that per-company fee inflation, not a growing filer base, is driving the aggregate.

Limitation: aggregate “total fees” figures across report years mix audit, audit-related, tax, and other fees. This report separates the audit-fee component wherever the source does. The registrant population also shifts year to year (SPAC waves in 2020-2021, delistings), which affects averages independent of any per-company fee change.

Section 2: Fee trends over time (2003-2024)

The clearest through-line is a sustained, roughly 4x rise in the average audit fee since Sarbanes-Oxley took effect. The table below assembles verified average-audit-fee and total-fee data points published by Ideagen Audit Analytics.

Notes on the series:
– Average audit fees rose for the third consecutive year in FY2024, which IAA attributes to increasing complexity and regulatory demands (Ideagen Audit Analytics, Sept 2025).
– Average audit fees hit an all-time high of $2.24 million in FY2022, an 11 percent jump over FY2021 (Ideagen Audit Analytics, 2023 report).
– Non-audit fees as a share of total fees fell from about 36 percent in FY2002 to a low of 9 percent in FY2021, reflecting Sarbanes-Oxley restrictions on auditor-provided non-audit services (Ideagen Audit Analytics, 20-year review via Harvard Law School Forum on Corporate Governance, Nov 2022).

Contradiction to flag: a separate primary industry study, the Financial Education and Research Foundation (FERF, part of Financial Executives International) 15th Annual Audit Fee Survey, reported an average public-company audit fee of $3.01 million in 2023, up 6.4 percent from $2.83 million in 2022. These numbers are higher than the IAA figures for the same years because the FERF study is a voluntary survey of a smaller, larger-company-skewed respondent set (about 50 public companies plus reference to more than 4,000 SEC filers), whereas IAA aggregates the full disclosed population. The two should not be treated as interchangeable.

Section 3: Big Four vs non-Big-Four fee levels and market share

Two different denominators are used across sources, and conflating them produces the single most common error in audit-market commentary. This report keeps them separate.

• Share of total SEC-registrant audit-fee payments to the Big Four was 69.5 percent in FY2024, with 250-plus other firms sharing 30.5 percent (Ideagen Audit Analytics, Sept 2025).
• Within the large-company universe, the concentration is far higher: the Big Four earned 99.7 percent of S&P 500 audit fees in FY2022 (Ideagen Audit Analytics, FY2022 S&P 500 analysis).
• In FY2022, across all SEC registrants, IAA reported Big Four firms accounted for about 92 percent of audit fees, with PwC at 28 percent ($4.66 billion), EY 25 percent ($4.27 billion), Deloitte 23 percent ($3.81 billion), and KPMG 16 percent ($2.74 billion) (Ideagen Audit Analytics, 2023 report).
• PwC’s average fee per client was $5.52 million in FY2024, with roughly a 20 percent market share, and EY held just under 20 percent (Ideagen Audit Analytics, Sept 2025).

Why the FY2022 (~92 percent) and FY2024 (69.5 percent) figures differ: the ~92 percent is the Big Four share of audit fees among all registrants, while the 69.5 percent is the Big Four share of all fee payments (a payment-distribution measure across the FY2024 registrant set). Different bases and different report methodologies produce different percentages. The consistent, unambiguous finding is that Big Four dominance rises sharply with company size, approaching total among the largest filers.

Section 4: Audit-fee-to-revenue ratios

Scaling fees to revenue shows that, despite record dollar fees, audit cost intensity relative to company size has been flat to declining.

• All SEC registrants paid $612 in audit fees per $1 million of revenue in FY2024, down 1 percent from $619 in FY2023 (Ideagen Audit Analytics, Sept 2025).
• In FY2022, all registrants paid $576 per $1 million of revenue, a 6 percent decrease and a nine-year low (Ideagen Audit Analytics, 2023 report).
• S&P 500 companies paid only $343 per $1 million of revenue in FY2022, reflecting scale economies at the largest firms (Ideagen Audit Analytics, FY2022).
• In FY2024, non-accelerated filers paid $1,349 and accelerated filers $2,201 per $1 million of revenue, versus $523 for large accelerated filers (Ideagen Audit Analytics, Sept 2025).
• Foreign private issuers paid $638 per $1 million of revenue in FY2024, higher than the $606 for U.S. companies (Ideagen Audit Analytics, Sept 2025).
• A Manufacturers Alliance survey put the average audit-fee-to-revenue ratio at 0.09 percent in 2025 for its manufacturer members (Manufacturers Alliance, May 2026).

What the numbers mean: smaller filers pay several times more per revenue dollar than the largest filers. The fee-to-revenue ratio at the very top (large accelerated filers, S&P 500) is a fraction of that borne by accelerated and non-accelerated filers, quantifying a fixed-cost, regressive structure in audit pricing.

Limitation: per-revenue ratios move with revenue as much as with fees. The FY2022 nine-year low partly reflects post-pandemic revenue rebounds inflating the denominator, not fee relief.

Section 5: Auditor concentration among large filers

• The Big Four audited over 78 percent of all U.S. public companies and 99 percent of all public-company sales in 2003 (GAO-03-864, July 30, 2003).
• The overall public-company audit market had a Herfindahl-Hirschman Index of 2,300 in 2006, above the 1,800 threshold the DOJ and FTC use to flag a “highly concentrated” market (GAO-08-163, 2008).
• 82 percent of Fortune 1000 companies viewed their auditor choice as limited to three or fewer firms in 2008, and about 60 percent viewed competition in their audit market as insufficient (GAO-08-163, 2008).
• The market for smaller public companies (revenue of $500 million or less) was much less concentrated than the large-company segment as of 2006 (GAO-08-163, 2008).
• There were 1,544 PCAOB-registered firms at the end of 2024, but many perform no issuer audits: 87 U.S. firms performed only one to five SEC-issuer audits and 112 U.S. firms audited only broker-dealers (PCAOB, 2024 Annual Report).
• PCAOB-registered firms fell about 6 percent to 1,444 by the end of 2025, and 58 percent of firms that withdrew cited performing no PCAOB-regulated work (PCAOB / Accounting Today, 2025).

What the numbers mean: the raw count of registered firms overstates real competition. A large majority of registrants do little or no issuer audit work, so effective choice for a large public company narrows to the Big Four plus a small set of “challenger” firms. The GAO concentration figures are dated (2003, 2008) but remain the most authoritative federal measurements; no newer official U.S. HHI for the audit market was located.

Section 6: International context (UK)

• The UK Big Four earned 98 percent of FTSE 350 audit fees in 2023 and 2024, a higher fee-share concentration than the US SEC-registrant market (Financial Reporting Council, Dec 2024 update).
• Non-Big Four firms held about 2 percent of FTSE 350 audit fees in 2024 by value but had grown to 13 percent of FTSE 350 audit engagements by count in 2023, up from 4 percent in 2019 (Financial Reporting Council, Dec 2024 update).
• Total UK Public Interest Entity audit fees reached GBP 1.4 billion in 2023, a 27 percent increase over 2022 (Financial Reporting Council, Dec 2024 update).
• Of the 23 FTSE 350 companies that changed auditor in the reporting year, 20 switched from one Big Four firm to another (Financial Reporting Council, Dec 2024 update).

Context: the UK provides a useful comparison because its regulator publishes market-share data directly, unlike the US where concentration figures depend on dated GAO studies and paywalled commercial data. The pattern is consistent across both markets: fee-share concentration is near-total among the largest listed companies.

Original synthesis: three derived insights

Insight 1: The Audit Fee Inflation Multiple (2003-2024)

Formula: FY2024 average audit fee divided by FY2003 average audit fee.
Calculation: $2,726,000 / $681,000 = 4.00x.
Inputs: Ideagen Audit Analytics FY2003 average audit fee ($681,000, 2023 report) and FY2024 average audit fee ($2,726,000, Sept 2025).
Result: the average U.S. public-company audit fee is 4.0x its 2003 level in nominal terms over 21 years, a compound annual growth rate of about 6.8 percent.
Limitation: nominal, not inflation-adjusted; the registrant mix changed materially over the period (SOX-era additions, SPAC waves, delistings), so the average company in 2024 is not the same as in 2003.

Insight 2: The Small-Filer Audit Cost Penalty (FY2024)

Formula: non-accelerated filer fee-per-revenue divided by large accelerated filer fee-per-revenue.
Calculation: $1,349 / $523 = 2.58x.
Inputs: Ideagen Audit Analytics FY2024 audit fees per $1 million of revenue by filer type (non-accelerated $1,349; large accelerated $523; accelerated $2,201) (Sept 2025).
Result: non-accelerated filers pay about 2.6x more in audit fees per revenue dollar than large accelerated filers, and accelerated filers pay about 4.2x more ($2,201 / $523), quantifying a regressive, fixed-cost fee structure that weighs hardest on mid-size companies.
Limitation: revenue-scaled ratios are sensitive to the denominator; smaller filers with very low revenue can distort the ratio upward.

Insight 3: The Concentration Gradient by Company Size (FY2022-FY2024)

Logic: compare Big Four fee share across three nested populations to show how concentration scales with size.
Inputs: Big Four share of all-registrant fee payments 69.5 percent (FY2024, IAA); Big Four share of all-registrant audit fees ~92 percent (FY2022, IAA); Big Four share of S&P 500 audit fees 99.7 percent (FY2022, IAA).
Result: Big Four fee dominance climbs monotonically with company size, from roughly 70 percent of all fee payments across every registrant to essentially 100 percent among the S&P 500. The “auditor choice” problem is concentrated almost entirely at the top of the market; competition, where it exists, is a small-filer phenomenon.
Limitation: the three data points use two different fiscal years and two different denominators (fee payments vs. audit fees), so the gradient is directional rather than a single-year like-for-like series. It should be read as a structural pattern, not a precise curve.

Tables

Average audit fee vs total auditor fee by year (US SEC registrants)

FY2024 average audit fee by filer type (US)

FY2024 average audit fee by sector (US)

Auditor concentration snapshots

Charts to create

1. “US Average Audit Fee, 2003-2024” (line). Data: average audit fee by year. Source: Ideagen Audit Analytics. Insight: the 4x rise since SOX. Citation-worthy because it is the single clearest long-run cost trend for public companies.
2. “The Small-Filer Penalty: Audit Fees per $1M Revenue by Filer Type, FY2024” (bar). Data: $523 / $2,201 / $1,349. Source: IAA. Insight: mid-size and small filers pay multiples of what the largest filers pay per revenue dollar.
3. “The Concentration Gradient: Big Four Fee Share by Company Size” (stepped bar). Data: 69.5% all registrants, 99.7% S&P 500. Source: IAA. Insight: dominance scales with size.
4. “US vs UK Large-Cap Auditor Concentration” (paired bar). Data: 99.7% S&P 500 (FY2022) vs 98% FTSE 350 (2023-24). Sources: IAA, FRC. Insight: near-total concentration in both major markets.
5. “Non-Audit Fees as a Share of Total Fees, 2002-2021” (line). Data: 36% to 9%. Source: IAA via Harvard corpgov. Insight: the SOX effect on auditor independence.

Methodology

Source selection prioritized Tier-1 primary sources (GAO reports, PCAOB filings and annual report, UK FRC publications) for market structure and concentration, and the leading Tier-2 industry compiler (Ideagen Audit Analytics) for aggregate fee levels, because IAA is the only source that systematically aggregates SEC-filing fee disclosures. IAA’s granular datasets are paywalled; only figures published in free reports, press releases, blog posts, or cited by the press were used, and all such figures are labeled Tier-2. The FERF/FEI Annual Audit Fee Survey was included as a second Tier-2 industry source and explicitly distinguished from IAA because it is a voluntary survey with a different, larger-company-skewed sample.

Inclusion rule: a figure was included only if it carried an identifiable year, geography, and traceable source with a working URL. Exclusion rule: any figure that could not be verified, or that appeared only behind a paywall without a free citation, was excluded. Conflicting numbers (for example, 2023 average fees of $2.516M per IAA versus $3.01M per FERF, and Big Four shares of ~92 percent versus 69.5 percent) were retained side by side with an explanation of the differing samples and denominators rather than reconciled into a single number. Derived figures (Insights 1-3) were computed only from verified inputs and their formulas and limitations are stated inline. No fee totals were fabricated. Date of last update: 2026-06-29.

Source quality ranking

Tier 1 (primary, government, official bodies):
– U.S. GAO, GAO-03-864 (July 2003) and GAO-08-163 (2008): auditor concentration, HHI, Big Four market share. Dated but authoritative; flagged as such.
– PCAOB 2024 Annual Report: registered-firm counts and issuer-audit distribution.
– UK Financial Reporting Council, Dec 2024 audit market and competition update: FTSE 350 and PIE fee shares.
– Underlying SEC proxy/annual-report fee disclosures are the ultimate primary source for all fee figures, though they were not aggregated here directly.

Tier 2 (credible market research from primary filings, public-company data):
– Ideagen Audit Analytics (formerly Audit Analytics): aggregate US fee levels, trends, concentration, per-revenue ratios. Granular data PAYWALLED; only free-summary figures used.
– FERF / Financial Executives International 15th Annual Audit Fee Survey (Dec 2024): survey-based average fees, flagged as a different sample.
– Manufacturers Alliance Audit Fee Benchmark (2025): sector-specific fee-to-revenue ratio.

Tier 3 (reputable journalism/commentary used only to locate or corroborate Tier-1/2 figures):
– Accounting Today, CPA Practice Advisor, TheCorporateCounsel.net, Harvard Law School Forum on Corporate Governance (which republished the IAA 20-year review).

Excluded: any paywalled IAA table not surfaced in a free summary; academic working papers whose figures could not be tied to a current dataset; social-media posts; and the raw IAA and PCAOB PDFs that did not render machine-readable text (their headline figures were verified via free summaries and press citations instead).

Citation format (per major statistic)

• Source: Ideagen Audit Analytics, Audit Fee Trends analysis, September 2025 (FY2024 data).
• Source: Ideagen Audit Analytics, Audit Fee Trends 2003-2022, July 2023.
• Source: U.S. Government Accountability Office, GAO-03-864, Public Accounting Firms: Mandated Study on Consolidation and Competition, July 30, 2003.
• Source: U.S. Government Accountability Office, GAO-08-163, Audits of Public Companies, 2008.
• Source: Public Company Accounting Oversight Board, 2024 Annual Report.
• Source: UK Financial Reporting Council, Audit Market and Competition Developments 2024 Update, December 2024.
• Source: Financial Education and Research Foundation (FEI), 15th Annual Audit Fee Survey, December 2024.

Journalist-friendly additions

Most quotable statistics

• The average U.S. public company paid a record $3.26 million to its auditor in FY2024, up 9 percent (Ideagen Audit Analytics, Sept 2025).
• U.S. public companies paid $21.675 billion in total auditor fees in FY2024 (Ideagen Audit Analytics, Sept 2025).
• The average public-company audit fee has quadrupled since 2003, from $681,000 to $2.726 million (Ideagen Audit Analytics).
• The Big Four earned 99.7 percent of S&P 500 audit fees in FY2022 (Ideagen Audit Analytics).
• The Big Four audited 99 percent of all U.S. public-company sales as far back as 2003 (GAO-03-864).

Data limitations

• The only comprehensive US audit-fee dataset (Ideagen Audit Analytics) is paywalled; figures here come from free summaries and are Tier-2.
• Federal concentration data (GAO) is from 2003 and 2008; no newer official US HHI was located.
• 2023 average-fee figures differ between IAA and FERF because of different samples and definitions.
• Big Four share percentages vary with the denominator (fee payments vs audit fees) and fiscal year.
• Per-revenue ratios move with revenue, not just fees.

Downloadable dataset, recommended fields (for Dataset schema)

fiscal_year, geography, metric_name, metric_value, unit, filer_type, sector, firm_or_group, denominator_basis, source_name, source_tier, source_url, methodology_note, last_updated.

150-word press summary

U.S. public companies paid a record $21.675 billion in fees to their external auditors in fiscal 2024, according to Ideagen Audit Analytics, whose data is drawn from SEC filings. The average company paid $3.26 million in total auditor fees, up 9 percent year over year, with the audit-fee component alone averaging $2.726 million. Average audit fees have quadrupled since 2003, when they stood at $681,000. The market remains highly concentrated: the Big Four firms (PwC, EY, Deloitte, KPMG) received 69.5 percent of all SEC-registrant fee payments in 2024 and 99.7 percent of S&P 500 audit fees in 2022. Federal data underscores the pattern, with the GAO reporting the Big Four audited 99 percent of public-company sales as far back as 2003. Fees per revenue dollar edged down to $612 per $1 million in 2024, showing costs rose slower than company revenues even as absolute fees hit records.

Five suggested headlines

• U.S. Public Companies Paid a Record $21.7 Billion in Audit Fees in 2024
• The Average Audit Fee Has Quadrupled Since 2003
• Big Four Firms Collect Nearly All S&P 500 Audit Fees
• Small Public Companies Pay Up to 4x More in Audit Fees per Revenue Dollar
• Two Decades On, the Audit Market Is Still an Oligopoly

10 FAQs

1. How much did U.S. public companies pay in audit fees in 2024? A total of $21.675 billion across 6,656 SEC registrants (Ideagen Audit Analytics, Sept 2025).
2. What is the average public-company audit fee? $2.726 million for the audit component and $3.26 million in total auditor fees in FY2024 (IAA).
3. How much have audit fees risen over time? From $681,000 average in 2003 to $2.726 million in 2024, about 4x (IAA).
4. What share do the Big Four hold? 69.5 percent of all SEC-registrant fee payments in FY2024 and 99.7 percent of S&P 500 audit fees in FY2022 (IAA).
5. Which sector pays the most? Finance, at an average $4.055 million in FY2024 (IAA).
6. Do small companies pay more relative to size? Yes; non-accelerated filers paid $1,349 per $1 million of revenue in FY2024 versus $523 for large accelerated filers (IAA).
7. How concentrated is the market historically? The Big Four audited over 78 percent of public companies and 99 percent of sales in 2003 (GAO-03-864).
8. What was the audit market HHI? 2,300 in 2006, above the 1,800 “highly concentrated” threshold (GAO-08-163).
9. How many audit firms are there? 1,544 PCAOB-registered firms at end-2024, but most do little or no issuer audit work (PCAOB).
10. How does the UK compare? The Big Four earned 98 percent of FTSE 350 audit fees in 2023 and 2024 (FRC).

Sources

1. Ideagen Audit Analytics, “Audit Fees Continued to Climb in 2024” (FY2024 data, Sept 2025). https://www.auditupdate.com/post/audit-fees-continued-to-climb-in-2024
2. Ideagen Audit Analytics, “The Average Audit Fee Reached an All-Time High in 2022.” https://www.auditupdate.com/post/the-average-audit-fee-reached-an-all-time-high-in-2022
3. Ideagen Audit Analytics, “Audit Fee Trends 2003-2022” report (July 2023). https://www.auditanalytics.com/doc/2023_Audit_Fees_Report.pdf
4. Ideagen Audit Analytics, “Audit fee trends of S&P 500.” https://www.ideagen.com/thought-leadership/blog/audit-fee-trends-of-sp-500
5. Harvard Law School Forum on Corporate Governance, “Twenty-Year Review of Audit and Non-Audit Fee Trends” (Nov 2, 2022, republishing Audit Analytics). https://corpgov.law.harvard.edu/2022/11/02/twenty-year-review-of-audit-and-non-audit-fee-trends/
6. TheCorporateCounsel.net, “Audit Fees: 20 Years of Trend Data” (Oct 2025). https://www.thecorporatecounsel.net/blog/2025/10/audit-fees-20-years-of-trend-data.html
7. U.S. Government Accountability Office, GAO-03-864, “Public Accounting Firms: Mandated Study on Consolidation and Competition” (July 30, 2003). https://www.gao.gov/products/gao-03-864
8. U.S. Government Accountability Office, GAO-08-163, “Audits of Public Companies: Continued Concentration in Audit Market for Large Public Companies Does Not Call for Immediate Action” (2008). https://www.gao.gov/products/gao-08-163
9. U.S. Government Accountability Office, GAO-08-163 Highlights. https://www.gao.gov/assets/gao-08-163-highlights.pdf
10. Public Company Accounting Oversight Board, 2024 Annual Report. https://assets.pcaobus.org/pcaob-dev/docs/default-source/about/administration/documents/annual_reports/2024-annual-report.pdf
11. UK Financial Reporting Council, “Audit Market and Competition Developments 2024 Update” (Dec 2024). https://media.frc.org.uk/documents/Audit_market_and_competition_developments_2024.pdf
12. CPA Practice Advisor, “Average Audit Fees Rose 6.4% in 2023, Report Finds” (Jan 2025, citing FERF/FEI 15th Annual Audit Fee Survey). https://www.cpapracticeadvisor.com/2025/01/02/average-audit-fees-rose-6-4-in-2023-report-finds/153834/
13. Manufacturers Alliance, “Audit Fee Benchmark 2024/2025.” https://www.manufacturersalliance.org/research-insights/audit-fee-benchmark-2024
14. Accounting Today, “Most PCAOB-registered firms didn’t do audits.” https://www.accountingtoday.com/news/most-pcaob-registered-firms-didnt-do-audits

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