Mergers and acquisitions involve serious financial exposure, and a due diligence audit is your safety net before committing millions to a deal. These audits examine everything from revenue recognition to hidden liabilities, and getting the scope and cost right separates smart buyers from those who stumble into problems post-closing. Here's what you need to know to budget accurately and hire the right firm.
What's Actually Included in an M&A Due Diligence Audit
A due diligence audit goes deeper than a standard financial audit. The auditor examines three to five years of historical financials, tests the validity of reported earnings, validates asset valuations, and identifies contingent liabilities. They'll also assess revenue quality (how sustainable are those sales?), analyze customer concentration, review contracts for change-of-control clauses, and evaluate working capital normalization.
Key areas examined typically include:
- Revenue and receivables: Testing sales transactions against contracts, shipping documents, and bank deposits to confirm revenue is real and properly timed
- Inventory and asset valuations: Verifying inventory counts, obsolescence reserves, and the condition of fixed assets
- Payables and accruals: Identifying undisclosed liabilities, pending claims, and accrued expenses that might not appear on the balance sheet
- Intercompany transactions: Unwinding non-recurring transactions or inflated sales between related entities
- Compliance and regulatory: Confirming the target company has no pending violations, environmental liabilities, or tax issues
- Tax positions: Reviewing tax returns for aggressive positions or contingent liabilities the IRS might challenge
The depth varies. A quick "red flag" review might focus on the largest revenue streams and obvious risks. A comprehensive audit digs into transaction-level testing and off-balance-sheet items.
What You'll Actually Pay
Due diligence audit costs depend heavily on company size, deal complexity, and how messy the financials are.
Small acquisitions ($5–50M revenue): Expect $25,000–$75,000. Smaller firms or boutique audit practices may handle this tier affordably.
Mid-market deals ($50–500M revenue): Budget $75,000–$250,000. This is where most deals cluster, and pricing reflects the work needed to test controls and validate multi-year trends.
Large transactions ($500M+ revenue): $250,000–$500,000+. International operations, multiple divisions, complex accounting, or manufacturing environments push costs higher.
Add-on costs that catch buyers off guard:
- Tax due diligence: $15,000–$100,000 (separate from financial audit, assesses tax risk)
- Environmental or legal diligence: varies, but often $10,000–$50,000
- Specialist reviews (IT systems, real estate valuations, etc.): $5,000–$75,000 each
- Accounting adjustments modeling: included in some quotes, but clarify upfront
Timeline matters too. A 4–6 week engagement costs less than a 12-week deep dive. Scope creep—finding data quality issues that require expanded testing—can add 20–30% to the original estimate.
How to Compare Providers and Control Costs
Start by getting specific about what you actually need. Are you buying a stable, mature business with clean records? A six-week focused audit might suffice. Are you acquiring a growth company with aggressive accounting or complex revenue models? Plan for 10–12 weeks and expect higher fees.
Request proposals that break down hourly rates by seniority level. Big Four firms (Deloitte, EY, KPMG, PwC) charge $300–$500+ per hour for senior staff. Regional firms typically run $150–$300 per hour. Boutique or smaller practices may offer $100–$200 per hour but may lack depth in specialized areas.
Ask prospective auditors:
- How many similar-sized deals have you completed in this industry?
- What's your process for identifying off-balance-sheet liabilities?
- Do you model normalized earnings, or just verify as-reported?
- How much fieldwork is done on-site versus remote?
Mercoly helps you compare and find trusted audit and assurance providers in one place, making it easier to request proposals side-by-side and see what different firms include.
Frequently Asked Questions
Q: Should I hire the same firm doing my purchase accounting or a separate firm for due diligence? A separate due diligence auditor brings independence and skepticism; your purchase accounting firm later records the adjustments you discover. Many deals use two firms for this reason.
Q: What red flags should push me to expand due diligence scope mid-engagement? Significant revenue concentration in one customer, frequent manual journal entries, a recent change in accounting methods, or inventory write-downs are typical triggers to dig deeper and expect higher final fees.
Q: How detailed does a due diligence report need to be for my lender or board? Banks typically require a written report identifying all material risks, quantified adjustments, and unadjusted differences; your board needs an executive summary and a list of deal breakers or renegotiation items.
Start by identifying your deal size and complexity, then request detailed proposals from three to five firms to compare pricing and expertise.