Locked Box vs. Completion Accounts

Most deal teams treat the choice of pricing mechanism — completion accounts versus locked box — as a drafting preference rather than what it actually is: a structural decision about where economic risk sits, who controls the information, and how much trust you are willing to place in your counterparty.

The thesis is simple. The locked box is not merely a seller-friendly shortcut, and completion accounts are not merely buyer protection. Each mechanism embeds a fundamentally different theory of what a purchase price is — and choosing wrong, or choosing lazily, creates dispute risk that no amount of clever SPA drafting can eliminate.

How Locked Box and Completion Accounts Allocate Risk Differently

The distinction reduces to a single question: when does economic ownership of the target transfer from seller to buyer?

Under completion accounts, the answer is: at completion. The buyer pays a provisional price on closing day, typically based on estimated working capital, net debt, and cash. After completion — usually within 60 to 90 days — the buyer's accountants prepare a set of closing accounts reflecting the target's actual financial position at the moment of transfer. If working capital is below the agreed target, the price adjusts downward, pound for pound. If above, it adjusts upward. The seller carries economic risk until the keys change hands, and the buyer pays only for what it demonstrably receives.

Under a locked box, the answer is different: at some agreed historical date, typically the most recent audited balance sheet date or a set of accounts prepared specifically for the transaction. The purchase price is fixed at signing by reference to this historical snapshot, and it does not adjust after completion. From the locked box date forward, the buyer is treated as the economic owner. The target is being run, in theory, for the buyer's benefit — even though the seller still legally controls it. To protect the buyer against value extraction during this interim period, the seller covenants not to allow any leakage (dividends, management fees, intra-group transfers, bonuses) from the target, backed by a pound-for-pound indemnity.

Same deal economics. Same enterprise value. Same equity bridge. But entirely different allocation of information asymmetry, interim risk, and post-completion administrative burden.

Why Completion Accounts Disputes Are So Common in M&A

The completion accounts mechanism is the default in US private M&A and remains widespread globally. Its appeal is intuitive: you pay for what you get. The SRS Acquiom 2020 M&A Deal Terms Study found that 90% of US deals included some form of post-closing purchase price adjustment. The mechanism has the comforting quality of precision — the final number is derived from actual financial data, not estimates or historical proxies.

But precision is not the same as accuracy, and the mechanism's apparent objectivity conceals several structural vulnerabilities that reliably produce disputes.

Working Capital Subjectivity and Accounting Judgment

The completion accounts process requires someone — usually the buyer, since it now controls the target's books — to prepare a set of financial statements as at a specific date. This sounds mechanical. It is not. Working capital is riddled with judgment calls: provisions against receivables, inventory obsolescence reserves, accrued liabilities, revenue recognition cut-offs, deferred income classification. Each of these involves estimates, and estimates can be made aggressively or conservatively. Data consistently shows receivables reserves and excess and obsolete inventory as the two most common sources of working capital disputes — precisely the line items where accounting judgment is widest.

The buyer, having just acquired the company, has every incentive to take a conservative view of these balances. Lower working capital means a lower final price. The seller, having just lost control of the books, has limited ability to challenge the methodology but every incentive to do so. The SPA will specify that the completion accounts should be prepared on a basis consistent with the target's historical accounting policies — but consistent with is doing an extraordinary amount of work in that sentence. Does it mean identical treatment, or the same general principles applied to potentially different facts? If the target historically reserved 5% against receivables over 90 days, and the buyer now believes 8% is more appropriate given new information obtained post-completion, is that consistent?

Post-Completion Information Asymmetry Between Buyer and Seller

Here is the structural problem that most deal teams under-appreciate. Before completion, the seller holds the information advantage — it knows the business, controls the records, and can see where the bodies are buried. After completion, this advantage inverts entirely. The buyer now controls the books, the systems, the employees, and the accounting judgments. The seller, particularly a private equity seller that has distributed proceeds to LPs, is in the worst possible position to challenge a set of accounts prepared by a party with both the motive and the means to shade the numbers.

When the economic environment deteriorates and it looks like the buyer may have overpaid, the buyer will sometimes look to claw back value through the purchase price adjustment process. This is not necessarily bad faith. It is simply what happens when you design a mechanism that places the preparation of economically significant financial statements in the hands of the party that benefits from one direction of error.

The Cost of Completion Accounts Disputes

Even when completion accounts do not produce a formal dispute, they impose significant costs. The buyer must dedicate finance team resources to preparing the accounts during the critical first 90 days of ownership — exactly when those resources should be focused on integration. The seller must retain advisers to review and challenge the accounts. Both sides negotiate over individual line items in a process that can drag on for months. Where the SPA provides for expert determination of disputed items, add another layer of cost and delay.

For a mid-market deal with an enterprise value of, say, $75 million, a completion accounts dispute over working capital might involve a $2-4 million swing in the purchase price. The advisory and legal costs of resolving that dispute — even short of formal proceedings — can easily run to $200,000-500,000 per side. That is a dead-weight cost borne by the transaction, funded ultimately by the investors on both sides.

How the Locked Box Mechanism Works — And Where It Creates Risk

The locked box emerged in the early 2000s as European private equity sponsors, running competitive auction processes, sought a mechanism that would produce clean, comparable bids and eliminate the post-completion haggling that was consuming management time and souring buyer-seller relationships. The logic was straightforward: if you force every bidder to price off the same historical balance sheet, you get an apples-to-apples comparison. And if you eliminate post-completion adjustments, you remove the single largest source of M&A disputes.

It worked. The CMS European M&A Study, which analyses hundreds of transactions annually across 27 European jurisdictions, has tracked the locked box's rise from niche PE tool to mainstream pricing mechanism. By 2020, locked box structures were used in 53% of European deals surveyed by CMS. The 2025 edition of the study — covering 582 deals advised on by CMS in 2024 — confirmed that locked box structures continue to feature prominently, particularly in non-PPA scenarios. In the UK, the locked box is now the dominant mechanism for PE exits and auction processes. One survey from the European mid-market found locked box structures in roughly 60% of deals without post-closing adjustment.

But the locked box is not a free lunch. Its elegance creates specific risks that buyers must understand and price.

Locked Box Date Staleness and Working Capital Deterioration

The locked box date is, by definition, in the past. In a typical deal, the locked box accounts might be dated 31 December, with signing in March and completion (following regulatory approvals) in June. That is a six-month gap during which the buyer bears economic risk in a business it does not control. If the target's working capital deteriorates during that period — because of seasonal demand patterns, customer losses, or an unforeseen downturn — the buyer has no recourse through the pricing mechanism. The price was fixed at signing. The leakage indemnity covers only value extracted by or for the seller, not operational deterioration.

This is a real risk. Consider a target with £2 million in normalised working capital at the locked box date. If seasonal demand or an operational hiccup reduces working capital to £1 million by completion, the buyer has effectively overpaid by £1 million — with no adjustment mechanism to compensate. Under completion accounts, this shortfall would flow directly into a pound-for-pound price reduction.

Leakage Risk and Permitted Leakage in Locked Box Deals

The locked box's principal protective mechanism is the leakage covenant: the seller promises that no value will leave the target between the locked box date and completion, except for specifically enumerated items of permitted leakage that the buyer has agreed and priced into the deal. In theory, this is a bright-line test — either value leaked or it did not.

In practice, the boundary between ordinary course trading and leakage can be blurry. Intra-group payments on arm's-length terms are typically permitted, but arm's length is itself a judgment. Management bonuses paid in the ordinary course might be permitted leakage, while deal-related bonuses would be prohibited — but a retention bonus designed to keep key employees through the transition might sit uncomfortably between the two categories. Transfer pricing within a group can be adjusted in ways that extract value without technically breaching the leakage covenant.

The seller also remains in operational control of the business during the gap period, creating a form of moral hazard. While the SPA will contain conduct-of-business covenants restricting unusual expenditures or commitments, the seller has limited incentive to invest in or improve a business whose economic benefit now accrues to someone else. This is the locked box's version of the lame duck problem.

Due Diligence Requirements for Locked Box Transactions

Because the buyer cannot true-up the price after completion, it must get comfortable with the locked box accounts before signing. This front-loads the diligence effort. The buyer needs to understand not just the target's financial position at the locked box date, but the quality and sustainability of that position — the normalised level of working capital, the appropriateness of provisions and reserves, the completeness of accruals. Any diligence failures cannot be remedied through a pricing adjustment; they become warranty and indemnity claims, which are harder to pursue and subject to contractual limitations (baskets, caps, time limits) that a pound-for-pound adjustment is not.

This is why the locked box is sometimes described as "seller-friendly." But a more accurate description is that the locked box rewards preparation. A well-prepared seller that provides clean, audited locked box accounts and comprehensive vendor due diligence is offering the buyer genuine price certainty. A seller that presents opaque accounts and resists diligence requests is using the locked box structure to shift risk it has not earned the right to shift.

Why US M&A Rarely Uses the Locked Box — And Whether That's Changing

One of the more interesting features of M&A market practice is the locked box's persistent failure to gain traction in the United States. Despite its widespread adoption in Europe, the mechanism remains a relatively foreign concept in US private M&A — relegated to special situations and often looked upon with suspicion by wary buyers.

This is not a mechanical problem. US deal lawyers understand the locked box perfectly well. The resistance is cultural and structural.

First, the US M&A market developed its pricing infrastructure around the completion accounts model. The ecosystem of independent accountants, working capital dispute resolution procedures, and post-completion adjustment mechanics is deep and well-understood. Law firms, accounting firms, and deal participants all have institutional muscle memory for this process. Switching to a locked box requires retraining — not just on the legal drafting, but on the entire workflow of how a deal is priced and closed.

Second, US buyers have historically enjoyed significant leverage in completion accounts disputes, precisely because of the information asymmetry flip described above. The buyer prepares the accounts, controls the books, and makes the judgment calls. A well-advised US buyer can recover meaningful value through an aggressive (but defensible) completion accounts process. The locked box eliminates this optionality.

Third, the US market lacks the auction-driven dynamics that powered the locked box's adoption in Europe. European PE exits are typically run as structured auction processes where bid comparability is paramount. US deals are more frequently bilateral negotiations or limited processes where the seller does not need the locked box's comparability advantages and the buyer is reluctant to accept its pricing constraints.

But this may be changing. As cross-border deal activity increases and US sponsors become more familiar with European deal structures, the locked box is appearing in more US transactions — particularly those involving European targets or European PE sellers. Several US law firms have published notes in recent years exploring the mechanism's potential benefits for domestic deals, and the hybrid structures emerging from deal practice — where a locked box is combined with a limited post-completion true-up on specific items — suggest the market is searching for a middle ground.

When to Use a Locked Box, Completion Accounts, or Hybrid Mechanism

The choice between locked box and completion accounts should be driven by deal-specific factors, not market convention or adviser preference. Here is a framework for thinking through the decision.

Favour the locked box when:

• The seller is running a competitive auction and bid comparability matters.
• The target has stable, predictable working capital with limited seasonality.
• The locked box date is recent (ideally within 3-4 months of expected completion).
• The target's accounts are audited or have been subject to comprehensive vendor due diligence.
• Both parties want a clean break with no post-completion tail.
• W&I insurance is being used, which further reduces the seller's post-completion exposure and makes a fixed price more palatable for all parties.

Favour completion accounts when:

• The gap between signing and completion is long or uncertain (waiting for regulatory approvals, for example).
• The target has volatile or seasonal working capital, making a historical snapshot unreliable.
• The buyer has limited visibility into the target's financial reporting and wants the ability to verify balances post-completion.
• The target is a carve-out from a larger group, where allocation of shared costs, intercompany balances, and standalone adjustments create genuine uncertainty about the right number.
• The deal is bilateral and the seller does not need auction-process efficiency.

Consider a hybrid when:

• The parties want the certainty of a locked box but one or two specific items — typically net debt or a particular contingent liability — genuinely cannot be fixed at signing.
• In this case, a locked box on working capital combined with a limited post-completion adjustment on the identified items can give both sides what they need.

There is a trend toward these tailored hybrid structures as dealmakers sought to bridge valuation gaps without accepting the full complexity of traditional completion accounts.

Reducing M&A Purchase Price Disputes: What the Data Shows

The choice of pricing mechanism is a choice about where to locate the deal's residual uncertainty. Completion accounts locate it after closing, in a process controlled by the buyer. The locked box locates it before signing, in the diligence process. Neither eliminates uncertainty. Both merely move it.

The mistake most deal teams make is treating this as a legal drafting question rather than a commercial one. The lawyers will tell you what the mechanism does. But the decision about which mechanism to use should be driven by the commercial team's assessment of where the risks actually sit — and which party is better positioned to bear them.