Customer concentration: what the evidence actually says
One big customer is supposed to cost you a full turn on your multiple. That figure has no source. What the research does show is different, more specific and more useful.
Every article about selling a business tells you the same thing about one big customer, usually with a number attached. A customer above a quarter of your revenue costs you a full turn on the multiple. Above a third and buyers move to an earn-out.
Start with what is actually at stake, because the arithmetic is simpler than the argument. On €1.2m of revenue, a customer worth 35% of it is €420,000 a year that can leave in one phone call. That is the thing a buyer is pricing: not the percentage, but the size of the hole.
We went looking for where the "full turn" figure comes from. It comes from other articles saying the same thing.
What we could not find
The "one turn" claim appears on business broker sites, M&A advisory blogs and content marketing pages. None of them cites a study, a dataset or a transaction sample. Follow the citations and they lead to each other or nowhere.
The related "10% rule," that a single customer above a tenth of revenue triggers a penalty, has no traceable origin either. It looks like lender covenant practice and public-company segment disclosure thresholds retrofitted as a valuation rule.
What the research does show
This is the part worth having, because it is specific and it is peer-reviewed.
Concentration makes investors want a higher return. A 2016 study in the Journal of Accounting and Economics found that suppliers with concentrated customer bases have a higher cost of equity capital, meaning investors demand more return for the same profits. The effect is stronger where the supplier is more likely to lose the customer, and it survives the usual statistical checks. The same direction shows up in the cost of debt. One nuance worth knowing: concentration in government customers goes the other way and lowers the cost of equity.
It makes lending more expensive. A 2017 study in the Journal of Financial Economics found that higher customer concentration raises interest rate spreads, adds restrictive covenants and shortens the term of loans.
And it changes how buyers behave. This is the closest thing to direct evidence on transactions. A 2022 study in the Journal of Business Finance and Accounting, covering US deals from 1985 to 2016, found that acquirers place fewer bids for targets with greater customer concentration, and use more stock payment when they do bid. Buyers of concentrated targets also did worse afterwards.
Read those three together and the mechanism is clear without a fabricated number:
| What concentration does | Evidence | Effect on your sale |
|---|---|---|
| Raises cost of equity and debt | Two studies, 2016 and 2017 | A buyer's model discounts your cash flows harder |
| Reduces the number of bidders | M&A study, 2022 | Less competition, which is what actually sets price |
| Shifts payment towards stock | M&A study, 2022 | You carry risk after the sale instead of banking cash |
The second row is probably the one that costs you money. Price in a private sale is set by competition far more than by anyone's discount rate. Fewer bidders is a worse outcome than a larger discount applied by one bidder.
The honest caveat
All three studies are on listed companies, the kind that file accounts with a stock market regulator. None of them tells you what happens when a €3m turnover fabricator with one customer at 40% goes to market.
The direction is very likely to carry over, because the mechanism is not exotic: a business that can lose half its revenue in one phone call is riskier, and risk is priced. But anyone who tells you the size of the effect for a business your size is telling you something nobody has measured.
What to do instead of arguing about turns
Change what a buyer is actually afraid of. The fear is not concentration itself, it is the probability and consequence of losing that customer. Contract length, notice period, renewal basis and assignability all move that probability, and unlike the multiple, they are things you can change in a year.
Know your concentration by profit, not by revenue. A large customer who is expensive to serve is a different risk from a large customer who is cheap to serve. Our guide on cost to serve walks through the calculation; the short version is that ranking customers by revenue and ranking them by what they leave behind produce different lists.
Expect the structure to move before the price does. If the 2022 study is right that concentrated targets attract fewer bids and more stock consideration, the negotiation you should prepare for is about deal structure, not headline value. An earn-out is a buyer pricing a risk they cannot otherwise underwrite.
Widen the base if you have time. Not because it moves a multiple by some published amount, but because it increases the number of buyers who can get comfortable, and the number of buyers is the thing that sets your price.
What this does not tell you
We have not established that customer concentration lowers SME transaction prices, because no published study establishes it. We have established that it raises the cost of capital and reduces bidder interest in a population of larger, listed companies, and given a reason to expect that direction to hold.
Nor does any of this address the other side. A 2012 paper in The Accounting Review found customer concentration associated with higher accounting returns, through lower operating costs per unit of sales and better use of assets. Serving one large customer is cheaper than serving fifty small ones. Concentration buys operating efficiency while it sells financing flexibility. It is a trade, and a buyer who only sees one side of it is mispricing your business in a direction you can argue about.
Sources
- Dhanraj Dhaliwal, J. Scott Judd, Matthew Serfling and Sarah Shaikh, "Customer concentration risk and the cost of equity capital," Journal of Accounting and Economics 61(1), 2016, pp. 23–48. https://econpapers.repec.org/RePEc:eee:jaecon:v:61:y:2016:i:1:p:23-48
- Murillo Campello and Janet Gao, "Customer concentration and loan contract terms," Journal of Financial Economics 123(1), 2017, pp. 108–136. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2442314
- C. S. Agnes Cheng, Rita Jaggi and Steven Young, "Customer concentration of targets in mergers and acquisitions," Journal of Business Finance & Accounting 49(7–8), 2022, pp. 1314–1355. US transactions 1985 to 2016. https://onlinelibrary.wiley.com/doi/10.1111/jbfa.12587
- Panos N. Patatoukas, "Customer-Base Concentration: Implications for Firm Performance and Capital Markets," The Accounting Review 87(2), 2012, pp. 363–392. https://papers.ssrn.com/sol3/papers.cfm?abstract_id=1666497
- BizBuySell, 2025 Year in Review, and GF Data, Small-Deal Resilience H1 2025, for the size of the disagreement between datasets. https://www.bizbuysell.com/blog/2025-year-in-review/ and https://gfdata.com/small-deal-resilience-h1-2025/
A note on the figure we did not use
The claim that customer concentration above a given threshold costs a full turn on the multiple appears widely and has no primary source that we could locate. We have left it out. Where we could not find evidence, this article says so rather than borrowing someone else's confidence.