Customer Concentration: The Number That Quietly Halves Your Multiple

Customer concentration is the risk that hides in plain sight. A business with one customer at forty percent of revenue can look wonderful from the inside: loyal, stable, predictable. To a buyer it reads as a single sentence that can undo the whole deal. What happens if that customer leaves? Concentration is not a sales problem. It is a valuation problem, and it is one of the few numbers that can quietly halve your multiple.

Why it moves the price so much

A buyer is not paying for last year's revenue. They are paying for the durability of next year's. One dominant customer makes that durability fragile: a single lost contract can wipe out the earnings the whole price was built on. So the buyer does what any rational buyer does. They discount. Smaller businesses feel this hardest, because a 40 percent customer is a larger share of a smaller base, which is part of why a EUR 500k EBITDA business trades at a lower multiple than a EUR 5m one. Concentration compounds the small-firm discount.

Where it hides, and where it drifts

The management meeting says nobody is really over ten percent. The CIM narrative agrees. Then the customer schedule two pages later lists the top account at twenty-two percent of revenue. Same document, two numbers, and the one that reaches the investment committee is usually the friendlier one. Concentration rarely hides because anyone lied. It drifts: in a rounded-down sentence, a summary that smooths the edge off, a schedule nobody reconciled against the story.

The concentration checks that actually matter

Check	Why it matters	Where to find it
Top-1 and top-5 customer share	The headline risk to the multiple	The revenue-by-customer schedule, not the narrative
Contract terms of the top account	A 30-day-notice contract is not a moat	The actual contract: notice period, exclusivity, change-of-control
Three-year trend	Is concentration growing or easing?	Customer schedules across periods
Margin concentration	The big customer may also be the low-margin one	Gross-margin-by-customer, where it exists
Hidden concentration	One end-customer behind several resellers or entities	Cross-check parent companies and end-users

The pattern is the same each time: take the figure from the schedule, not the sentence, and tie it to the contract that governs it. If a concentration number cannot be traced to a specific line, it is not a number yet. It is a diligence request.

A worked example

On the call, management says the business is well diversified, nobody over fifteen percent. The customer schedule on the next page of the same CIM lists the top account at about twenty-two percent of revenue. That is not a lie you caught. It is a number that drifted in conversation. But if you price the deal on the spoken version, you have underwritten a concentration risk you never saw, and the investment committee approved it without ever seeing the schedule. The reconciliation is what surfaces it, and the gap between fifteen and twenty-two percent can be worth a full turn of EBITDA.

How Deal OS surfaces it

This is one of the contradictions Deal OS is built to catch. It reads the CIM narrative, the customer schedule, and the contracts, and where the stated concentration disagrees with the underlying schedule, it flags the contradiction with both figures cited rather than smoothing it into one clean sentence. Every claim in the brief traces to its source page or is dropped before it reaches a memo. You can see it run on a synthetic deal in the sample brief, where two customer-concentration figures a page apart quietly disagree.

Want it on your own deal? Run one real CIM through it for a one-time $99 with the CIM Pass: a mutual NDA is built in so the file never leaves the workspace, and the $99 is credited to your first month if you continue.

Pair this with the management meeting cross-check and the M&A due diligence checklist: the checklist tells you what to verify, the management meeting is where the spoken version drifts, and the schedule is where the truth is written down.

Frequently asked questions

What is customer concentration in M&A? It is the share of a company's revenue that comes from its largest customer or customers. High concentration means a single lost account can materially damage earnings, which is why buyers treat it as a valuation risk rather than a sales metric.

How much customer concentration is too much? There is no fixed line, but many buyers grow cautious once a single customer passes 15 to 20 percent of revenue, and treat anything above 30 to 40 percent as a serious risk that reshapes price and deal structure.

How do buyers adjust valuation for customer concentration? Through a lower multiple, more of the price shifted into earn-outs or seller notes, tighter contractual protections, or, if the risk is severe enough, walking away.

How do I verify customer concentration in diligence? Take the figure from the revenue-by-customer schedule rather than the narrative, check it against the actual contract terms of the top accounts, and look at the trend over several years. Any number that cannot be traced to a schedule or contract is a diligence request, not a fact.

See what a cited, contradiction-flagging brief looks like on a sample deal at Deal OS.