Tax due diligence is the tax-focused workstream of buy-side due diligence — a systematic review of a target's tax positions, history and exposures. Its twin goals are to uncover hidden tax liabilities the buyer could inherit and to inform the most tax-efficient structure for the deal. Run by tax advisers or a transaction-advisory team, it sits alongside financial, legal and commercial diligence and feeds directly into price, structure and the agreement.
What it examines
Tax diligence sweeps across every tax a business touches:
- Income tax — federal, state and local: filing history, positions taken, open audits, reserves, and the use/limitation of attributes like NOLs (§382) and credits.
- State-and-local nexus and sales-and-use tax. A frequent source of nasty surprises: a target selling across states (or online) may have failed to collect sales tax where it had economic nexus (post-Wayfair), creating large, unbudgeted exposures.
- Payroll and employment tax — withholding, and especially worker classification (independent contractors vs employees), a common exposure.
- Transfer pricing — for multinational targets, whether intercompany pricing is defensible (key in cross-border deals).
- Entity and transaction history — the validity of the S-election (vital if a §338(h)(10) or F-reorg is planned), prior reorganizations, and any QSBS qualification the seller is claiming.
- Other — R&D credits, property tax, unclaimed property/escheat, and incentive arrangements.
Why it matters: inherited liability
The stakes are highest in a stock deal, where the buyer inherits the target entity with all its tax history — including unfiled returns, unpaid taxes and aggressive positions that a future audit could unwind. Even in an asset deal, successor-liability rules and bulk-sales / sales-tax clearance requirements mean tax exposures can follow the assets. Tax diligence is how the buyer finds these before they become its problem.
How findings flow into the deal
Identified exposures translate directly into deal terms:
- Price — quantified exposures may reduce the price or be carved out;
- Specific indemnities and escrow/holdback — known issues (a sales-tax exposure, a contested position) are often backstopped by a dedicated indemnity or escrow rather than general reps;
- R&W insurance — note that insurers typically exclude known tax issues, so diligence findings shape what the policy will and won't cover; and
- Structure — diligence confirms whether the planned structure (step-up, election, reorganization) actually works given the target's facts.
Strong tax diligence is therefore not just defensive — it is what makes the deal's tax structuring reliable, and is a core reason tax specialists are engaged from early in the buy-side process.
See also
- Due diligence — The structured investigation a buyer conducts on a target between LOI and closing — covering financial, legal, tax, commercial, operational, IT, HR and environmental workstreams — to verify the seller’s claims, find risks and shape final price and deal terms.
- Indemnification — The contractual mechanism by which the seller compensates the buyer (or vice versa) for losses resulting from breaches of representations, warranties or covenants in the definitive agreement.
- NOL preservation (Section 382) — U.S. Internal Revenue Code Section 382, which limits a corporation's ability to use pre-acquisition net operating losses after a more-than-50% ownership change.
- Deferred tax in M&A — The deferred tax assets and liabilities recognised on differences between book and tax basis of assets and liabilities acquired in a business combination.
- QSBS in M&A — Qualified Small Business Stock — Section 1202 — provides a federal capital-gains exclusion of up to $10M (or 10x basis) on the sale of qualifying C-corp stock held more than five years.
- M&A accountant — CPA or transaction-services accountant who runs quality-of-earnings analysis, working-capital benchmarking, tax structuring and post-close purchase-price allocation work.