1.Deloitte
London, United KingdomLargest of the Big Four by total revenue at $70.5 billion FY2025. Audit and assurance is one of its core service lines, covering statutory audit for listed and private companies globally.
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Business Companies
Review leading auditing firms serving USA clients, with company profiles that explain each provider's expertise, delivery focus and fit.
Use the comparison to build a shortlist, then review each company profile for its specialty, location and approach.
Updated October 10, 2026
Side-by-side comparison of leading providers serving USA clients
| Company | Specialty | Location | Website |
|---|---|---|---|
| #1Deloitte | Largest of the Big Four by total revenue at $70.5 billion FY2025. | London, United Kingdom | Visit site |
| #2PwC (PricewaterhouseCoopers) | Second-largest Big Four firm, auditing a large share of the Fortune Global 500 alongside its advisory and tax practices. | London, United Kingdom | Visit site |
| #3EY (Ernst & Young) | Big Four firm with global assurance practice, reporting $24.15 billion total revenue for 2025. | London, United Kingdom | Visit site |
| #4KPMG | Fourth Big Four firm, valued at $15.20 billion in 2025, with audit as a core service line alongside tax and advisory. | Amstelveen, Netherlands | Visit site |
| #5RSM US LLP | Largest US firm outside the Big Four, with a substantial middle-market assurance practice. | Chicago, IL, USA | Visit site |
| #6BDO USA | Mid-market firm providing assurance services alongside tax and advisory, with FY2025 revenue of $3.018 billion. | Chicago, IL, USA | Visit site |
| #7Grant Thornton | Founded 1924, providing audit and assurance to middle-market and growth companies. | Chicago, IL, USA | Visit site |
| #8Baker Tilly | Top-ten US firm providing audit and assurance alongside tax and advisory to middle-market organizations. | Chicago, IL, USA | Visit site |
| #9Forvis Mazars | Top-ten US firm providing assurance services, formed from the combination of Forvis and Mazars. | Springfield, MO, USA | Visit site |
| #10CBIZ / Mayer Hoffman McCann | CBIZ provides accounting services with attest and audit work performed by its affiliate Mayer Hoffman McCann under a separate structure. | Cleveland, OH, USA | Visit site |
Use this comparison to identify a shortlist, then review the detailed company profiles and USA buyer’s guide below.
Review the available information for each provider before requesting references, pricing and a project proposal.
Largest of the Big Four by total revenue at $70.5 billion FY2025. Audit and assurance is one of its core service lines, covering statutory audit for listed and private companies globally.
Visit website →Second-largest Big Four firm, auditing a large share of the Fortune Global 500 alongside its advisory and tax practices.
Visit website →Big Four firm with global assurance practice, reporting $24.15 billion total revenue for 2025.
Visit website →Fourth Big Four firm, valued at $15.20 billion in 2025, with audit as a core service line alongside tax and advisory.
Visit website →Largest US firm outside the Big Four, with a substantial middle-market assurance practice.
Visit website →Mid-market firm providing assurance services alongside tax and advisory, with FY2025 revenue of $3.018 billion.
Visit website →Founded 1924, providing audit and assurance to middle-market and growth companies.
Visit website →Top-ten US firm providing audit and assurance alongside tax and advisory to middle-market organizations.
Visit website →Top-ten US firm providing assurance services, formed from the combination of Forvis and Mazars.
Visit website →CBIZ provides accounting services with attest and audit work performed by its affiliate Mayer Hoffman McCann under a separate structure.
Visit website →Compare delivery models, rates, contracts and risk before selecting a provider for a US engagement.
This page lists 10 auditing firms providers that work with United States clients. We look at delivery track record, whether the team overlaps with US time zones, how they scope and price work, and whether they can sign standard US contracts including an MSA, SOW, NDA and mutual indemnity.
Firms currently featured include Deloitte, PwC (PricewaterhouseCoopers), EY (Ernst & Young), and KPMG.
Delivery footprints on this list span London, United Kingdom, Amstelveen, Netherlands, Chicago, IL, USA, and Springfield, MO, USA, so you can choose between onshore US delivery, nearshore teams with 3–5 hours of overlap, and offshore teams priced for volume work.
US buyers usually see three engagement models for auditing firms: fixed-scope projects, time and materials with a monthly cap, and a dedicated team retainer. Onshore US consultancies typically bill $121–$250 per hour, nearshore partners in Latin America $55–$95, and offshore teams $25–$55.
Ask for a rate card by role, not a blended rate — a blended number hides how much of the work is done by junior staff. For fixed-bid work, insist on a written change-order process, and for retainers, confirm the notice period and any minimum monthly hours.
Watch the total cost of ownership: discovery workshops, knowledge transfer, post-launch support, and the cost of taking the work back in house at the end.
Before you sign, confirm the provider carries professional liability (E&O) and cyber insurance with US-acceptable limits, and that the MSA clearly assigns IP ownership of all deliverables to you on payment.
If the engagement touches regulated data, get the compliance posture in writing: SOC 2 Type II for the provider's own systems, HIPAA with a signed BAA for health data, CCPA/CPRA handling for California consumer data, GLBA for financial services, and background-check policies for anyone with production access.
Also nail down worker classification and subcontracting — many US buyers require written approval before any part of the work is passed to a third party.
Run the same questions past two or three firms from this list and compare the answers side by side — the differences are usually more revealing than the proposals.
Practical answers for USA clients comparing providers, pricing and engagement models.