11 Best Outsourced Audit Support Service Companies for U.S. CPA Firms

19 September 2025

• Outsourced audit support service companies help CPAs and audit firms expand capacity, meet deadlines, and maintain audit quality without increasing full-time headcount.
• Mid-size and specialized providers offer co-sourced audit support with strong documentation practices, industry familiarity, and flexible engagement models.
• Key selection criteria include audit expertise, data security, review workflows, scalability, software compatibility, and alignment with your audit methodology.

Audit firms and CPA practices across the U.S. are under growing pressure to deliver high-quality audits faster, with fewer resources, and under tighter regulatory oversight. Between staffing shortages during peak season, evolving compliance requirements from the PCAOB and SEC, and rising client expectations, many firms are struggling to meet deadlines without compromising quality. 

This isn’t just a capacity issue. Failing to deliver audit deliverables or documentation can expose firms to compliance risks and reputational damage. As a result, more firms are adopting outsourced audit support as a strategic solution to fill gaps, maintain quality, and drive efficiency. 

By outsourcing key audit functions, firms can access experienced professionals, improve workpaper consistency, and scale up as needed without the cost or complexity of hiring in-house. QX Accounting Services, for example, supports U.S. audit firms with over 100 trained auditors through a secure, structured audit co-sourcing model. 

Continue reading to explore why audit outsourcing is gaining momentum in 2025, how to evaluate potential partners, and the top 11 audit support providers that are helping firms strengthen their audit delivery. 

Why Businesses Outsource Audit Support Services (Key Benefits) 

1. Manage Peak Workloads & Project Surges 

Audit is cyclical: many firms have “busy season” surges. Outsourcing gives flexible capacity to absorb extra engagements without overhiring. 

2. Access Specialized Audit Talent 

Some audit tasks require deep technical skills (risk assessments, internal control testing, disclosures). Outsourced audit teams often bring specialized expertise not available internally. 

3. Improve Efficiency & Turnaround 

Outsourced teams, working in parallel or on night shifts, can advance audit fieldwork or document drafting, speeding the overall schedule. 

4. Maintain Quality & Compliance 

Audit support firms use structured review processes, maintain audit file standards, and stay current with regulatory changes, reducing the risk of deficiencies. 

5. Lower Fixed Costs & Risk 

Instead of hiring full-time auditors at a fixed cost, you pay only for the needed audit support. You also avoid turnover, training overhead, and workforce constraints. 

How to Choose the Right Outsourced Audit Support Service Company 

When selecting an audit support partner, prioritize: 

• Audit & Assurance Expertise: deep understanding of PCAOB, GAAS, internal controls, risk, and audit methodology. 

• Review & Quality Control Process: four‑eyes review, manager oversight, file checks, and documentation reviews. 

• Security & Data Safeguards: SOC 2, ISO certifications, encrypted transfer, and audit file protection. 

• Scalability & Staffing Models: ability to scale up/down; mix of onshore/offshore / nearshore; FTE, project, hybrid. 

• Technology & File Integration: ability to work in your audit software (Engagement, CaseWare, etc.), shared portals, e‑working papers. 

• Cultural & Communication Fit: language, time zones, audit terminology familiarity, and responsiveness. 

• Transparency & SLAs: clear deliverable timelines, roles/responsibilities, escalation protocols, and audit file ownership. 

Top Audit Outsourcing Companies for U.S. CPA Firms:

1. QX Accounting Services 

Key Audit Support Services: Audit planning, risk assessment, documentation, analytical procedures, lead schedules, and workpaper support. 
Location: Offshore delivery (India) with U.S. engagement teams. 
Best For: CPA firms needing secure, scalable audit co-sourcing. QX offers SOC 2 Type II and ISO 27001 compliance, U.S.-GAAP-trained teams, and proven experience supporting busy-season audit overflow for U.S. firms. 

2. CapActix 

Key Audit Support Services: External audit file prep, internal audit assistance, forensic audit support, sales tax/IRS documentation. 
Location: India-based, serving U.S. firms. 
Best For: Firms looking to consolidate tax, bookkeeping, and audit support with one partner. CapActix offers flexible resource models and integrates well with CPA workflows. 

3. AcoBloom International 

Key Audit Support Services include audit documentation, planning file assembly, internal control testing, and industry-specific audit support (e.g., nonprofit, government). 
Location: Offshore (India), focused on U.S. CPA firms. 
Best For: Firms needing structured, co-sourced audit assistance alongside accounting/tax services. AcoBloom supports audit file consistency and timely delivery. 

4. Datamatics CPA (Audit & Assurance Services) 

Key Audit Support Services: Risk analysis, audit evidence collection, materiality calculations, working papers, and draft financials. 
Location: Offshore teams with U.S. audit support experience. 
Best For: Firms looking to fill recurring audit process gaps—particularly documentation and compliance-heavy areas. 

5. Schneider Downs 

Key Audit Support Services: Internal audit co-sourcing, audit staff augmentation, risk & control reviews, SOX compliance. 
Location: U.S.-based, serving mid-market and enterprise clients. 
Best For: Organizations seeking trusted internal audit capacity without hiring full-time. Schneider Downs combines expertise with scalable delivery. 

6. Riveron 

Key Audit Support Services: Internal audit co-sourcing, internal controls testing, audit remediation, and governance advisory. 
Location: U.S. offices with nationwide reach. 
Best For: Firms needing support on internal audit programs, especially those navigating regulatory, SOX, or risk-based audit scopes. 

7. IS Partners, LLC 

Key Audit Support Services: Internal audit outsourcing, compliance testing, process control documentation, and IT audit support. 
Location: U.S.-based; works across industries. 
Best For: Companies and CPA firms needing fractional internal audit services with industry-specific control expertise. 

8. CLA (CliftonLarsonAllen) 

Key Audit Support Services: Co-sourced internal audits, operational audits, IT audits, risk advisory, and control reviews. 
Location: U.S. nationwide network. 
Best For: CPA firms or clients needing internal audit muscle during growth, transformation, or compliance cycles. CLA brings deep domain experience. 

9. Protiviti 

Key Audit Support Services: Internal audit, co-sourcing, enterprise risk services, and control testing under a consulting model. 
Location: U.S. and global offices. 
Best For: Large firms and enterprises requiring sophisticated internal audit and compliance support with access to deep industry specialists. 

10. Crowe LLP 

Key Audit Support Services: Internal audit outsourcing, risk management, audit transformation, SOX readiness, and compliance advisory. 
Location: U.S.-based with global reach via Crowe Global. 
Best For: Audit and advisory firms needing scalable internal audit solutions with high compliance standards and technology integration. 

11. EisnerAmper (Outsourced Services Division) 

Key Audit Support Services: Internal audit support, enterprise risk services, controls testing, and audit process optimization. 
Location: U.S.-based with hybrid delivery models. 
Best For: Mid-sized to large clients needing audit and risk support from a nationally recognized accounting and advisory firm. 

How does audit support outsourcing differ from full audit outsourcing? 

Audit support outsourcing typically means the third party assists parts of the audit (documentation, risk evaluation, working papers, internal control testing) rather than owning the whole engagement. Full audit outsourcing may include taking over entire audit engagements and issuing reports. 

Is audit support outsourcing safe and compliant with PCAOB / SEC rules? 

Yes, if the partner understands U.S. audit and assurance standards (GAAS, PCAOB), uses robust review processes, and maintains strong information security protocols (SOC 2, encryption). Always check credentials, sample files, and review processes. 

Will outsourcing reduce audit quality or lead to deficiencies? 

Yes, there is risk if you choose a low-quality provider. But a reputable partner with rigorous reviews and certified auditors can improve consistency, reduce human errors, and enhance audit documentation quality. 

When should a firm outsource audit support? 

When internal audit staff is overloaded, when taking on new engagements, when talent is scarce, or when you want to free internal staff for higher-value tasks like client relationships, advisory, or quality control. 

What parts of audit can be outsourced? 

A: Many: planning & risk assessment, control testing, substantive testing, analytical procedures, drafting disclosures, review and documentation, sample selection, working paper formatting, wrap-up, etc. 

Final Thoughts

Outsourcing audit support has become a practical solution for CPA firms and audit practices dealing with capacity constraints, staffing shortages, and increasing documentation demands. The traditional approach of scaling through in-house hiring is no longer sufficient or cost-effective in a market where audit seasonality, regulatory pressure, and client expectations continue to grow.

Firms now require flexible capacity that can align with engagement schedules, maintain audit file consistency, and support compliance across multiple reporting frameworks. Outsourced audit support enables access to trained professionals who can assist with key components such as risk assessments, working papers, lead schedules, and audit documentation without diverting internal staff from client-facing or review-focused responsibilities.

The ability to delegate repeatable, documentation-heavy tasks to experienced teams frees audit partners and managers to focus on planning, client relationships, and quality control. It also provides a safeguard against late deliverables, inconsistent audit files, and overburdened internal teams. This is especially critical for firms navigating PCAOB oversight, complex multi-entity audits, or a growing book of audit engagements.

Each provider listed in this guide brings a specific value proposition, whether it’s deep U.S. audit expertise, secure delivery infrastructure, industry-specific knowledge, or scalable resource models. By selecting the right audit support partner, firms can protect engagement quality, manage their margins more effectively, and expand their capacity to serve more clients with confidence.

Why QX as Your Audit Support Partner: The QX Difference

• U.S. client service teams for coordination, onboarding, and file communication
• Teams trained in U.S. GAAS, GAAP, and CPA firm audit workflows
• SOC 2 Type II and ISO 27001 certified infrastructure for secure data handling
• Engagement models tailored to your audit cycle: FTE-based, per-engagement, or hybrid
• Staff experienced with leading audit software such as CaseWare, AdvanceFlow, and Excel-based systems
• Scalable delivery capacity to support firms during peak periods and ongoing audits

Divya Ramaswamy

Combining creative flair with a solid foundation in research-oriented content marketing, Divya assists accountants in understanding and navigating pressing industry issues. With a knack for distilling complex data into actionable advice, she helps professionals make informed decisions to enhance their practices.

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