You land a client that changes the scale of the business. Within twelve months they account for £900k of your £1.2m revenue. The relationship is excellent, the work is the kind you wanted when you started, and you have not thought much about winning anything else. Three years later, that same client still represents 70 per cent of your income. You have grown into them, not beyond them. The person who holds the relationship, the one the client calls first, is you.
That situation has a name and a set of financial consequences that tend to arrive all at once.
What is client concentration risk?
Client concentration risk describes the situation where a small number of clients hold a disproportionate share of revenue. Advisory and M&A sources treat a single client above 10 to 15 per cent as an early warning, and above 20 to 25 per cent as high risk. When your top three clients together exceed half of revenue, lenders and buyers typically treat your cash flow as volatile and price that into their terms.
The thresholds are not regulatory limits. They are drawn from advisory and M&A practice, but they appear consistently in due diligence checklists, lender risk models, and M&A commentary. A common pair of benchmarks that recur across acquisition and credit contexts: a single client above 20 to 25 per cent, or a top three collectively above 50 per cent.
Sector concentration adds a related dimension. If 70 to 80 per cent of your clients sit in one industry, a regulatory change or sector downturn can hit all your major accounts at roughly the same time, even if no individual client exceeds the revenue thresholds on its own.
Why does client concentration matter for your firm?
The core problem is that a concentrated client base introduces risk in three directions at once: your operating resilience, your borrowing terms, and your eventual exit value. Large accounts that represent a dominant share of your income will press for discounts, extended payment terms, and additional scope without charge. Over time, those concessions erode the margins that make the business worth owning.
For the exit scenario specifically, buyers look at whether the top client relationship is tied to you personally. Bender CFO Services has documented agencies where 75 per cent of revenue sat in a single client; when that relationship came under pressure, restructuring became the only option. GP Ventures, an M&A advisory firm, has reported cases from contract manufacturing where a single customer reached 90 per cent of sales, and potential acquirers either dramatically reduced their offers or walked away. The Corporate Finance Institute notes that high customer concentration is a standard factor in credit analysis and equity valuation, directly affecting discount rates and deal terms.
On the borrowing side, banks applying internal risk models under PRA and FCA supervision will often restrict the proportion of any single customer’s receivables they will advance against, or apply stricter covenants and higher interest rates where concentration is high.
Where will you actually feel it?
Concentration risk surfaces most visibly at the moments that matter most to a founder: when you try to refinance or raise working capital, when you start exploring a sale, or when the large client restructures its own supplier arrangements. The difficulty is that each of those moments is the wrong time to discover you have a dependency the other party already sees and has priced in.
In M&A due diligence, a single client above 20 to 30 per cent of revenue will prompt the buyer to examine whether the relationship is personal to you. If it is, the deal structure will often include an earn-out tied to that client renewing or hitting spend thresholds, a discount to the headline multiple, or a requirement that you remain in the business through a transition period.
In a bank finance conversation, the lender will look at the concentration within your debtor book and may cap the percentage of a single customer’s invoices they will advance against. If your major client also demands 60 to 90-day payment terms, the combined effect is a cash position that is fragile in a way a revenue figure alone does not reveal.
When the large client decides to renegotiate terms, bring work in-house, or cut its budget, the impact arrives quickly. The fixed-cost base was built around their spending level.
When should you accept concentration, and when should you act?
Acceptance is sometimes rational. A firm in a niche market with a handful of credible buyers will naturally carry a concentrated book, and lenders and investors who know that sector will read it as structural rather than mismanaged. The question is whether the concentration is deliberate, contractually protected, and has a credible diversification plan attached, or whether it simply accumulated without anyone deciding to let it.
An early-stage firm using a large anchor client to fund capability-building has a reasonable case for temporary concentration, provided it actively diversifies over the following two to three years. A services firm with a multi-year framework agreement, minimum spend commitments, and a 90-day termination clause is in a materially different position than one on rolling monthly purchase orders.
The situations where concentration becomes a problem regardless of intent are easier to identify: the large client knows the relationship is personal to you and uses that knowledge in every commercial conversation; the contract has no notice period or minimum spend clause; the client’s own sector is volatile; or the margins on the account are thin once you include the extras absorbed without charge. Under UK contract law there is nothing to prevent a large client insisting on onerous termination clauses, broad indemnities, and uncapped liabilities when you want the work. Combined with high revenue concentration, a single dispute can threaten the whole business.
What sits alongside client concentration risk?
Three related risks often travel with high concentration, and addressing the headline revenue number without recognising them will leave gaps. The first is sector concentration, where the bulk of your clients sit in one industry and a sector shock hits them simultaneously. The second is gross-profit concentration, where a large account covers your fixed overheads and the rest of the portfolio runs thin. The third is key-person risk in the client relationship itself.
Key-person risk compounds concentration directly. If you personally hold the senior relationship with every major account, a buyer will see the revenue as fragile without you retained. Advisory sources recommend introducing at least two senior contacts from your side into each major account and building relationships at multiple levels on the client side, operational, financial, and executive, so the account does not depend on one sponsor on either side.
For UK firms working with regulated clients, two further layers apply. If your major client is in financial services, the FCA’s guidance on outsourcing means your resilience profile may be scrutinised by their risk function as a condition of continuing the engagement. If the relationship ends, UK GDPR obligations under ICO guidance can require rapid data deletion and exit support that is expensive to deliver if you have not planned for it.
The most straightforward starting point on de-risking is an explicit exposure cap: a target to bring any single client below 25 per cent of revenue over two to three years, alongside a stronger contract with minimum spend and notice provisions. Advisory sources suggest prioritising new business that dilutes concentration rather than growth that doubles down on existing accounts.
The goal is a firm where the loss of any single client relationship, however painful, does not end the business. That shift changes what the business is worth to a buyer, who controls the commercial conversation with the large account, and how much stress accumulates when that client goes quiet for a week. If you want to think through where your firm sits and what a realistic de-risking plan looks like, Book a conversation.
