A business that earns most of its money from a few customers can look healthy on paper and still be fragile. If one of those customers leaves, renegotiates or runs into trouble of its own, the profit you paid for can shrink within months. That is why experienced buyers ask about customer concentration early, and why it so often becomes a point of negotiation during diligence. This guide explains how to measure it properly, how it affects value and financing, and how to shape a deal so that the risk is shared rather than carried by you alone.
Customer concentration describes how much of a business's revenue comes from a small number of customers. The higher it is, the more the business depends on decisions it does not control.
Due diligence is the investigation a buyer carries out before committing to a purchase, testing the finances, contracts, legal position and operations against what the seller has described.
What customer concentration means
Customer concentration describes how much of a business's revenue depends on a small number of customers. The usual starting point is the share of revenue from the largest customer, followed by the combined share of the top five and the top ten.
There is no single line where concentration becomes a problem. A customer worth 15% of revenue on a five-year contract with high switching costs may worry you less than one worth 12% that buys on purchase orders and has been cutting volumes. The percentages tell you where to look. The contracts, the relationship and the trend tell you how worried to be.
It also helps to separate customer concentration from its close relatives. Heavy reliance on one sales channel, such as a marketplace, an app store or a single search engine, is platform dependence (see dependence on one marketing channel). Heavy reliance on one supplier is supply concentration (see supplier or single-source manufacturing concentration). Each behaves differently, and a business can have all three at once.
How to measure it
Ask for revenue by customer for at least three financial years plus the trailing twelve months. It should be exported from the accounting or invoicing system, not typed into a spreadsheet by the seller. Then work through these steps.
- Group related customers. Subsidiaries of one parent, franchisees of one brand or departments of one public body often make a single buying decision. Treat them as one customer.
- Rank by gross profit as well as revenue. A large customer on thin margins matters less to profit than its revenue share suggests. A mid-sized customer paying full prices can matter more.
- Look at the trend. Is the top customer's share rising because it is buying more, or because everyone else is buying less?
- Check who the customer really is. A distributor or agency that resells to many end users can be a concentration risk in its own right, even when end demand is spread widely.
- Strip out one-off work. A large project inside the last 12 months can make a customer look bigger, and the business healthier, than next year will show.
A fictional example
Quillmarsh Packaging is a fictional UK distributor with revenue of £4,000,000 and gross profit of £1,000,000. Its largest customer, a regional food producer, buys £1,200,000 a year, which is 30% of revenue. The next four customers add £1,400,000, so the top five account for 65%.
On a gross profit basis the picture shifts. The largest customer negotiated keen prices and contributes £240,000 of gross profit, or 24%. The second largest pays list prices and contributes 15% of gross profit from 10% of revenue. Both relationships matter, and neither is visible in a listing that says only "loyal, long-standing customer base".
Trailing twelve months means the most recent 12 consecutive months of figures, whatever the financial year. It gives a more current view than the last set of annual accounts.
Why buyers discount for it
Concentration lowers value for several reasons, and they tend to compound one another.
Losing a customer hits profit harder than revenue. When a large customer leaves, most fixed costs stay. Staff, premises, vehicles and software do not shrink in step with sales. Suppose Quillmarsh's profit before the owner's pay is £400,000. Losing the largest customer would remove £240,000 of gross profit, or 60% of that figure, unless costs could be cut quickly.
Large customers have bargaining power. A customer that knows it matters can push prices down, stretch payment terms or ask for extra service. Some of that pressure may already be in the numbers. More may arrive when a new owner takes over and the customer tests the relationship.
A change of owner is a natural moment to leave. It gives a customer a reason to review its suppliers. In an asset sale, contracts often need the customer's consent to move to the new owner. In a share sale the contract stays with the same company, but a change of control clause can give the customer the right to walk away.
The relationship may belong to the seller. In many small businesses the largest accounts were won and kept by the owner personally. If that is the case, customer concentration and owner dependence are the same risk seen from two sides. The owner dependence guide explains how to test it.
Lenders see the same risk. A lender assessing an acquisition will ask what happens to loan repayments if the largest customer leaves. In the US, the SBA's rules for 7(a) loan applications from 1 October 2026 require the lender to obtain an independent quality of earnings report on most acquisitions priced at $3 million or more, and that report must assess customer concentration risk. Concentration can reduce how much you can borrow, which in turn changes what you can afford to pay. The financing guide covers how lenders test this.
In an asset sale you buy selected assets of a business; in a share sale (a stock sale in the US) you buy the company itself, with its full history. The choice shapes risk, tax and what needs consent.
A change of control clause gives the other party to a contract rights if the business changes owner, such as the right to terminate, renegotiate or refuse consent.
A quality of earnings review is an accountant's analysis of whether a business's reported earnings are accurate, sustainable and correctly adjusted. It is not an audit.
How Loupe's valuation reflects it
Loupe's free valuation tool asks for the largest customer's share of revenue and adjusts the multiple by band:
| Largest customer's share of revenue | Adjustment to the multiple |
|---|---|
| 10% to 25% | minus 5% |
| 25% to 50% | minus 15% |
| over 50% | minus 25% |
The adjustment applies to the low, likely and high multiples together. It is added to the other quality adjustments, such as recurring or contracted revenue, revenue trend and owner dependence, and the total is capped between minus 45% and plus 30%. A business with a dominant customer but mostly contracted revenue and a manager in place is therefore marked down less than one with a dominant customer and nothing to offset it.
As an illustration only, if a business's likely multiple before adjustments were 3.0, a minus 15% adjustment would bring it to 2.55. On earnings of £400,000 that moves the likely value by about £180,000 before rounding.
These results are indicative, not a formal valuation. The methodology page sets out every step, and you can try the calculation on any listing with the valuation tool.
Recurring revenue comes back without being won again each time, through subscriptions, retainers or service contracts. Contracted revenue is the part committed for a fixed term.
Not all concentration is equal
Two businesses with the same top customer share can carry very different risk. These features make concentration easier to live with:
- a written contract with a meaningful remaining term, no right to terminate for convenience and no change of control clause
- real switching costs, such as integration with the customer's systems, regulatory approvals or bespoke tooling
- several relationships inside the customer, across purchasing, operations and finance, not one contact who knows the owner
- a long record of steady or growing volumes at stable prices
- recurring or contracted revenue rather than one-off orders
- a customer that is financially sound and pays on time
These make it worse:
- purchase-order relationships that can stop at any time
- public sector or large corporate contracts due for re-tender soon after completion
- falling volumes, recent price cuts or a rising number of credit notes
- a customer that is under financial pressure, merging with another group or bringing the work in-house
- a relationship that rests on one person at the customer and one person at the seller
How to test it in diligence
Some of this work can start before you sign an NDA. The rest needs the seller's documents and, towards the end, the seller's agreement.
From the listing and public information. Look for phrases such as "key account", "major contract" or "preferred supplier to". Check the seller's website for case studies and logos that point to one dominant client. Public contract award notices and a customer's own announcements can reveal the size and end date of a contract.
From documents. Request revenue and gross profit by customer for three years plus the trailing twelve months, copies of the main customer contracts and any amendments, recent correspondence about pricing or renewal, aged debtors by customer and credit notes by customer. Reconcile the customer figures to the accounts so that the totals match. The diligence document request list sets these out in order.
From conversations. Ask the seller how each major customer was won, who manages it day to day, when it last went out to tender and how it reacted the last time prices rose. The questions for the first seller call include these. Late in the process, and only with the seller's agreement, a conversation with the largest customer is often the most useful hour of diligence you will spend. Sellers are understandably protective, so agree in advance what will and will not be said.
From checks on the customer. Company registry filings, credit reports and recent news tell you whether the customer's own business is stable enough to keep buying.
Non-disclosure agreement (NDA)
A non-disclosure agreement is a contract in which a potential buyer promises to keep information about a business confidential. Sellers usually ask for one before sharing the business's name or detailed figures.
Structuring a deal around a dominant customer
If the business is still worth buying, the structure of the deal can move some of the risk back to the seller, who knows the customer best. Common tools include:
- An earn-out that pays part of the price only if revenue or gross profit, from that customer or from the business as a whole, holds up over an agreed period.
- Seller finance with a right to reduce or offset repayments if the customer leaves within a set period. Whether an offset right works in practice, and how it sits alongside any bank loan, needs legal advice.
- A holdback or escrow of part of the price, released once the customer has renewed or a set period has passed.
- A condition to completion that the customer consents to the transfer of its contract or signs a renewal.
- A transition commitment from the seller to introduce you to the customer, attend key meetings with you and stay available for an agreed period.
- A lower price, which is simpler than any of the above and sometimes the right answer.
Each option has trade-offs. Earn-outs can lead to disputes about how the business was run after completion, and some lenders restrict them: SBA 7(a) acquisition loans in the US do not allow seller earn-outs. Holdbacks tie up the seller's money and may meet resistance. Conditions can delay completion. Have a lawyer and an accountant who act on acquisitions draft and review the terms, and raise the structure early, ideally before you agree a price in a letter of intent (heads of terms in the UK). The guide from first call to letter of intent covers that stage.
An earn-out is part of the purchase price paid only if the business meets agreed targets after the sale. It can bridge a gap between the seller's price and the buyer's view of the evidence.
Seller finance is when the seller lends the buyer part of the purchase price, to be repaid with interest after completion. It is also called vendor finance or a seller note.
A holdback is part of the purchase price the buyer keeps back at completion and pays later if no valid claims arise. Unlike escrow, the money stays with the buyer.
When to walk away
Concentration is usually something to price in rather than a reason to stop. It becomes a deal breaker when several warning signs line up: the largest customer supplies most of the profit, its contract ends or can be terminated soon after completion, the relationship rests entirely with a seller who will not stay on, and the seller will not share any of the risk through the structure. If the customer has already said it plans to cut volumes or move elsewhere, and the price does not reflect that, the gap is unlikely to close.
A seller's flat refusal to accept any deferred payment in this situation tells you something too. See refusal of any seller finance or earn-out.
Where Loupe fits
The red flag page on one customer above 20% of revenue lists the questions to ask and the documents to request, and the red flag screen helps you check a listing for this and other warning signs in a few minutes. Before you sign an NDA or pay an adviser, a Loupe dossier can look at who the business sells to, using the listing and public sources such as named clients and case studies, and turn what it finds into questions for the seller. It cannot see the seller's customer records any more than you can at that stage, so treat it as a way to decide whether a business deserves the next step. See what's in a dossier.