Locked Box vs Completion Accounts in M&A

When a buyer and seller agree on a price for a business, they almost never close the deal on the same day they shake hands. Weeks or months pass between signing and completion while regulators clear the deal and conditions are satisfied. The business keeps trading during that gap: it earns cash, pays down or draws debt, and its working capital moves. So the agreed headline number is never the whole story. The deal also needs a rule for how the final amount that changes hands reflects the state of the business at the moment ownership actually transfers.

There are two such rules, and the choice between them is one of the most negotiated points in any private M&A deal. Completion accounts set an estimated price at closing and then true it up afterward based on the company's actual balance sheet. A locked box fixes the price earlier, at a historical balance-sheet date, and uses contractual protections instead of a post-closing adjustment. Knowing how each works, who prefers which, and where each dominates is exactly the kind of practical deal knowledge that separates a candidate who has read about M&A from one who understands how deals are actually priced.

This post compares the two mechanisms head to head, walks through leakage and permitted leakage, explains value accrual, and covers the striking geographic split between Europe and the United States.

Here is the comparison every M&A interviewer wants you to be able to reproduce before getting into the detail.

The single idea that organizes the whole table is timing: a locked box fixes value at a date in the past and transfers risk from that date, while completion accounts fix value at the moment of closing and settle the difference afterward. Everything else, the leakage rules, the disputes, the diligence burden, follows from that one difference.

Completion accounts: fix the price after closing

Under completion accounts, the parties agree a price formula rather than a final number. At closing the buyer pays an estimated price based on expected cash, debt, and working capital. After completion, a set of accounts is drawn up showing the actual figures on the closing date, and the price is adjusted up or down for the difference.

Completion accounts

An M&A pricing mechanism where the buyer pays an estimated price at closing, then the price is trued up after completion based on accounts prepared as at the closing date. The adjustment reflects the actual cash, debt, and working capital delivered, so the buyer pays for the business exactly as it stood when ownership transferred.

The economic logic is that the buyer should pay for the company as it actually is on the day it takes control, no more and no less. If the target delivered more cash or less debt than estimated, the price goes up; if working capital came in light, the price comes down. This is why the net working capital adjustment sits at the heart of most completion-accounts deals.

Locked box: fix the price before signing

A locked box flips the timing. The parties pick a recent historical balance-sheet date, the locked box date, and fix the equity price using that balance sheet. From that date forward the box is "locked": the buyer is treated as the economic owner, and there is no post-closing adjustment for how the business performed in the meantime.

Locked box

An M&A pricing mechanism where the purchase price is fixed at signing using a historical "locked box" balance sheet. Economic risk and reward pass to the buyer from that historical date, and the seller covenants that no value has leaked out of the business since then, except for specifically permitted items. There is no completion-accounts true-up.

The practical effect is that the buyer steps into the seller's shoes as economic owner from the locked box date, even though legal ownership and payment only happen at completion. Whatever the business earns or loses in the meantime is the buyer's, which is why the seller can promise a fixed number and walk away clean once the deal closes. The buyer accepts that certainty in exchange for taking the risk that the historical balance sheet was accurate and that nothing untoward happens to the business before completion.

Leakage and permitted leakage

Because the buyer is paying for the business as it stood at the locked box date, the seller must not strip value out of it between that date and completion. Any such extraction is called leakage, and the seller gives covenants promising it will not happen, backed by a pound-for-pound (or dollar-for-dollar) indemnity.

Leakage

Value that flows out of the target to the seller or its related parties between the locked box date and completion, such as dividends, distributions, management or monitoring fees, or unusual bonuses. Because the buyer already owns these economics, leakage is repaid in full by the seller on top of the agreed price.

Not every payment is forbidden. The parties agree a list of permitted leakage, ordinary-course payments that are allowed because they were known and priced in. These typically include the seller's normal salary, pre-agreed dividends, interest on shareholder loans, and ordinary intra-group trading.

Value accrual and the deal timeline

Because the buyer gets the upside of the business from the locked box date but does not actually pay until completion, the seller usually charges a return for that gap. This value accrual (sometimes a fixed daily amount, sometimes an interest rate on the equity value) compensates the seller for leaving its capital in the business between the two dates. Conceptually, the cash that changes hands looks like this:

The locked-box process runs on a predictable sequence, which is part of its appeal in competitive sales.

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The estimate-and-true-up mechanism

Completion accounts keep the price live until after closing. The agreement specifies target levels for cash, debt, and working capital, and the price moves with the actuals. A simplified version of the settlement is:

The buyer pays the estimate at closing, then within an agreed window (often 60 to 90 days) the parties prepare accounts as at the completion date and settle the difference. This is why a thorough quality of earnings review and a clear understanding of the target's normalized working capital are so important: the target NWC peg is heavily negotiated, and a poorly set peg can hand value to either side.

Where the disputes happen

The defining feature of completion accounts is that the fight happens after closing. The seller has an incentive to present favorable accounts; the buyer, now in control of the business and its books, prepares or reviews them. Disagreements over accounting policies, working-capital definitions, and one-off items are common and sometimes go to an independent expert. The mechanism is more precise than a locked box, but it keeps the price open and adversarial for months after the deal is supposedly done.

The seller's case for a locked box

Sellers, especially private equity funds running an auction, love the locked box because it delivers price certainty and a clean exit. The number is fixed at signing, the cash received at completion is known, and there is no post-closing adjustment hanging over the distribution to fund investors. In a competitive process, a seller can also impose a single locked-box framework on every bidder, which keeps the auction clean and comparable. The trade-off is that the seller gives up any upside in the business after the locked box date, since the buyer owns that growth.

The buyer's case for completion accounts

Buyers often prefer completion accounts because they pay for the business as it actually is at closing, not as it looked on an older balance sheet. That protects them if cash, debt, or working capital deteriorate before completion. The cost is uncertainty and a heavier post-closing process. A buyer accepting a locked box is taking on more risk and therefore leans harder on diligence of the locked box accounts, since there is no true-up to correct a misstatement later.

One of the sharpest ways to show real-world knowledge is the geographic split. The locked box was developed in Europe and is now the dominant mechanism there, particularly in sponsor-led auctions. According to the CMS European M&A Study, the locked box was used in roughly 53% of European deals against 47% for completion accounts, having steadily gained share over the prior decade (CMS European M&A Study).

The United States is the mirror image. Completion accounts (often called closing accounts or a closing-date purchase-price adjustment) remain the default, and the locked box is comparatively rare, though it is gaining ground as American sponsors who learned the structure in European processes import it home (University of Pennsylvania, pricing mechanisms in M&A). Earlier CMS data illustrates how wide the gap once was, with closing accounts appearing in the large majority of US deals while the locked box steadily climbed toward a majority across European and UK transactions over the following decade. The momentum has run one way: the locked box keeps gaining share, helped by the rise of sponsor-led auctions on both sides of the Atlantic.

This divide is a frequent point in cross-border M&A, where a US buyer and a European seller may start from opposite default assumptions about how the price should even be set. A US acquirer used to negotiating a working-capital peg and a post-closing true-up can be surprised to be handed a fixed-price locked box with a permitted-leakage schedule, and the reconciliation of those expectations is itself part of the deal negotiation.

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The choice of mechanism changes where the analytical work goes. Under a locked box, the work is front-loaded: because there is no true-up, the buyer has to be confident in the locked box accounts before signing, so financial diligence on that balance sheet and tight drafting of the leakage definitions carry the weight. Under completion accounts, more of the work is back-loaded into preparing and contesting the closing accounts, and into negotiating the working-capital peg.

For anyone building the model, the mechanism also affects the sources and uses and the cash that actually moves at completion. A locked box deal pays a fixed equity price plus value accrual less leakage; a completion-accounts deal pays an estimate at closing with a later settlement. Either way, robust financial due diligence is what makes the chosen mechanism safe, by validating the balance sheet a locked box relies on or by pinning down the definitions a completion-accounts true-up will turn on.

Locked box versus completion accounts looks like a narrow drafting choice and turns out to encode the entire economics of how a deal transfers value: when the price is fixed, when risk passes, who carries the business through the gap between signing and closing, and where the inevitable arguments happen. The candidate who can explain that a locked box trades the buyer's certainty about the balance sheet for the seller's certainty about the price, and who knows that Europe and the US default to opposite mechanisms, is demonstrating the kind of grounded deal knowledge that interviewers reward.

When you study this, anchor everything to the one date that defines a locked box and the one moment that defines completion accounts. If you can narrate a deal forward from that date, through leakage, value accrual, and the cash that finally moves at completion, you have turned a pair of definitions into a working understanding of how private companies actually change hands.