Legal and advisory fees for M&A due diligence can reach up to 10% of total deal value. On a $20 million transaction, that's potentially $2 million in diligence cost — a number that reflects the enormous manual effort required to comb through financial statements, contracts, and disclosures. Understanding what drives that cost shows where it can be reduced.
What Drives the Cost
The cost is labor — professionals reading documents at professional billing rates. A data room holds hundreds of documents, and the legal, financial, operational, and tax workstreams each read their slice for red flags. The bigger the deal and the larger the data room, the more reviewer-hours required, and on the fixed 6-week timeline, more hours often means more people billing simultaneously. The reading is thorough because the cost of a missed red flag — discovered after close — dwarfs the diligence fee.
Vendor Diligence Adds to It
On the sell side, vendor (or reverse) due diligence — where the seller reviews their own business before going to market — costs $100,000 to $500,000 but can increase deal certainty by letting the seller control the narrative and address issues proactively. This is additional diligence spend on top of the buyer's, all driven by the same document-review labor.
How AI Changes the Economics
Because the cost is dominated by first-pass document reading, automating that pass directly attacks the largest cost component. The AI agent reads every document and produces the preliminary red-flag analysis, so professional time concentrates on the critical issues and negotiation rather than the volume reading — compressing the labor that drives diligence toward 10% of deal value. The agent is demonstrated at omnionlinestrategies.com/ai-agent-ma-due-diligence.