Tax Due Diligence in M&A: What It Finds and Why It Matters

Financial due diligence asks whether the earnings are real. Tax due diligence asks a darker question: what does this company owe that nobody has written down?

The distinction matters because tax exposures do not die at closing. In a stock deal, the buyer inherits every position the seller ever took, every state where nexus quietly accrued, every contractor who should have been an employee. The IRS and forty-some state revenue departments do not care whose name is on the cap table now.

What tax due diligence covers

A full tax due diligence review runs four layers deep. Federal income tax: return accuracy, uncertain positions, NOL carryforwards and the Section 382 limits that can gut their value. State and local tax: income, franchise, sales and use, and the nexus map that e-commerce and remote work have scrambled. Employment tax: payroll compliance and worker classification. And transaction-specific analysis: how the deal structure itself creates or destroys tax value.

The review works from returns, workpapers, and correspondence, then tests what it finds against how the business actually operates. The gap between the two is where exposures live.

The five exposures diligence finds most

Sales tax nexus leads the list, and it is rarely close. Since Wayfair, economic nexus rules mean a software or e-commerce company can owe tax in thirty states while filing in three. Uncollected sales tax compounds quietly, and unlike income tax, it was never the company's money to keep.

Worker classification comes second. Contractors doing employee work create payroll tax exposure plus penalties, and the modern remote workforce has multiplied the problem. Then come uncertain federal positions, R&D credits that will not survive exam, and state income tax filings that simply never happened.

Each finding gets quantified: tax, penalties, interest, look-back period. On a mid-market deal it is common for the total to reach seven figures, which is why the quality of earnings work and tax work run side by side.

Asset deals, stock deals, and who eats the history

Structure decides who owns the past. In an asset purchase, most historical exposures stay with the seller, and the buyer gets a stepped-up basis to depreciate. In a stock purchase, history transfers with the shares. Sellers usually want stock treatment, buyers usually want assets, and elections like a 338(h)(10) exist to split the difference.

None of that is a formality. The same target at the same price can produce materially different after-tax outcomes depending on structure, which is why tax diligence belongs at the deal-design table, not the signing dinner.

How findings land in the agreement

Quantified exposures move through the purchase agreement in a familiar sequence. Specific indemnities for identified risks. Escrows sized to the look-back window. Purchase price adjustments where the exposure is effectively certain. And in the sharpest cases, a requirement that the seller enter voluntary disclosure agreements before close, cleaning up the nexus problem at yesterday's prices.

Buyers running buy-side diligence should treat the tax workstream as leverage engineering. Sellers should treat it as a preview: everything a buyer will find, you could have found first.

Find it before they do

For sellers, the playbook is the same one that governs all exit readiness work. Run the nexus study early. Fix classification before a buyer prices it. Enter VDAs while you control the timeline.

BD Emerson runs tax due diligence for buyers and sellers as part of our M&A advisory services, integrated with financial due diligence so the two reports tell one story. The tax history is coming to closing either way. Better to know what it says.