Definition (canonical)
Due diligence is the systematic investigation of a business before a transaction — an acquisition, investment or major contract — to verify that reality matches what the seller claims. Its purpose is not to kill deals but to price risk: findings translate into price adjustments, warranties, escrows or, occasionally, walking away.
The scopes, by question asked
Legal DD: does the target cleanly own what it sells — corporate records, share title, key contracts and their change-of-control clauses, litigation, IP ownership (the classic startup failure: code copyrights never assigned by contractors). Financial DD: are the numbers real — quality of earnings, revenue recognition, one-offs dressed as recurring, debt and off-balance-sheet commitments. Tax DD: filings, disputes, aggressive structures that transfer to the buyer. Operational/commercial DD: customer concentration, churn, supplier dependencies, team retention risk. Scope scales with deal size and stakes: a full M&A process runs for weeks with virtual data rooms and specialist advisors on both sides; a routine supplier check compresses exactly the same logic into a few hours of desk work — see KYB for the counterparty-verification variant.
How the process actually runs
Buyer sends a request list → seller opens a virtual data room → advisors review and interview management → findings land in a DD report with issues ranked by severity. Good process discipline: start from the deal-breakers (title to shares, litigation that could sink the target, revenue authenticity) rather than boiling the ocean; every red flag gets a price: fixable (condition to closing), pricable (adjustment or escrow), or fatal.
Red flags that recur across deals
Reluctance to open the data room "before signing"; numbers that shift between meetings; one customer above ~30% of revenue; key contracts terminable on change of control; founder-dependent operations with no second line; disputes with former co-founders over IP. None is automatically fatal — undisclosed ones are, because they poison trust in everything else. Experienced buyers say the finding matters less than how the seller handles it: transparency converts problems into price points, evasion converts them into exits.
FAQ
Who pays for due diligence? Each side bears its own advisors' costs; buyers budget roughly 1–3% of deal value for a full process.
How long does it take? Supplier-level checks: days. SME acquisition: 3–6 weeks. Complex cross-border deals: months, often phased.
Can sellers prepare? Vendor DD — sellers auditing themselves pre-sale — shortens the process and prevents price erosion from surprises. Increasingly standard.
Related: KYB · Business Valuation · Balance Sheet Reviewed: 2026-07-15 · Sources: M&A practice