Locked Box vs Completion Accounts: M&A Pricing Mechanisms Explained

One of the most consequential decisions in structuring a private company sale isn't the headline price — it's how that price gets fixed and adjusted between signing and completion. The two dominant mechanisms, locked box and completion accounts, allocate risk, cash, and negotiating leverage very differently, and choosing between them shapes how the deal is priced, documented, and fought over if something goes wrong.

The Core Problem Both Mechanisms Solve

A share purchase agreement is usually signed before completion, sometimes with weeks or months in between for regulatory clearances or other conditions to be satisfied. During that gap, the target business keeps generating or consuming cash, and its balance sheet keeps moving. Both locked box and completion accounts exist to answer the same question — what price should the buyer actually pay given how the business has performed and changed between the valuation date and completion — just by very different routes.

Completion Accounts: Price It After the Fact

Under a completion accounts mechanism, the parties agree a price based on an estimated net asset value or net debt position at signing, then prepare a full set of accounts for the target as at the actual completion date, usually within 60-90 days afterward. The final price is adjusted up or down based on the difference between the estimated and actual completion-date figures, typically for net working capital, cash, and debt. If the business held more cash or less debt than estimated, the buyer pays more; if the reverse, the price is reduced.

This gives the buyer precision — they only pay for what they actually receive, measured at the point they take control. The cost is time, complexity, and dispute risk: completion accounts require detailed accounting policies to be agreed in the purchase agreement, a true-up process, and frequently an independent expert determination when the parties disagree on specific line items. This is one of the more common sources of post-completion disputes in private M&A, often running well into the months after closing.

Locked Box: Price It Upfront, Protect the Base Date

Under a locked box mechanism, the price is fixed by reference to a balance sheet as at a date before signing — the "locked box date" — and that price doesn't move at completion regardless of how the business has actually performed in between. Instead of adjusting the price after the fact, the purchase agreement includes strict covenants preventing "leakage": the seller cannot extract value from the business between the locked box date and completion (dividends, management fees, asset transfers, discharge of seller-related debt) other than specifically "permitted leakage" items agreed in the contract. If leakage does occur, the buyer has a pound-for-pound indemnity claim.

Locked box gives sellers certainty and a cleaner exit — no post-completion adjustment process, no independent accountant fees, no months of uncertainty over final proceeds. It has become the dominant structure on competitive private equity sell-side auctions in Europe in particular, because it lets a seller present a clean, fixed price to bidders and close faster. The trade-off for the buyer is pricing risk between signing and the locked box date: they're economically exposed to the business's performance over a period they don't yet control, relying heavily on leakage covenants and warranties rather than a true-up mechanism to protect their position.

Which Mechanism Gets Used

The choice is heavily influenced by deal dynamics rather than any universal rule. Competitive auction processes, particularly private equity exits, lean toward locked box because it's faster to close and gives sellers price certainty they can market to multiple bidders. Bilateral deals, carve-outs, or situations with significant uncertainty about the target's trading performance closer to completion more often use completion accounts, since the buyer will want the protection of paying for what it actually receives. Some deals use a hybrid: a locked box price with a specific "ticking fee" or interest mechanism that compensates the seller for value accruing in the business between the locked box date and completion, approximating the economics of a true-up without the full completion accounts process.

How This Connects to the Rest of the Deal

Pricing mechanism choice interacts with other deal terms. A locked box structure, by fixing price early, pairs naturally with sellers wanting a clean exit supported by warranty and indemnity insurance rather than a long tail of post-completion exposure. Where part of the consideration is contingent rather than fixed, such as an earn-out, the base completion mechanism still needs to be agreed for the certain portion of the price even though a share of the total consideration depends on future performance.

FAQ

Is locked box riskier for buyers than completion accounts?
In terms of pricing precision, yes — the buyer commits to a fixed price before seeing the completion-date financial position, relying on leakage protections rather than a post-completion adjustment.

Why do private equity sellers prefer locked box?
It delivers price certainty, a faster close, and avoids the cost and uncertainty of a post-completion true-up process, which matters when a fund needs to distribute proceeds to its investors promptly.

What is "leakage" in a locked box deal?
Any value extracted from the target business by the seller or its related parties between the locked box date and completion that isn't specifically permitted under the agreement, which gives the buyer a direct indemnity claim.

Deal pricing mechanisms and purchase agreement structuring are core topics across Learnsignal's CPD courses for finance professionals working in corporate finance and transaction services.