You’ve probably had a quarter like this. One client keeps commissioning more work, they pay promptly, the relationship is solid, and they now account for close to half your revenue. That feels like success. The problem surfaces later, when they restructure their procurement, bring the work in-house, or simply move on. The risk has been there all along. It has a name: client concentration.
What is client concentration?
Client concentration is the share of your total revenue that comes from your largest client or clients. A service firm where one customer accounts for 40% of annual turnover has high concentration. One where the top client is 10% does not. UK lenders explicitly ask for this figure when assessing creditworthiness, treating it as a direct measure of how fragile your revenue base is.
The concept comes from the finance and lending world. When a lender or an M&A buyer reviews your business, they want to know not just your total revenue but how evenly it is distributed. A firm with six clients at roughly equal shares is stable relative to one where a single relationship accounts for the majority of turnover.
Xeinadin Group, a UK accountancy firm, published a case study of a Twickenham marketing agency where one client represented around 50% of revenue. When that client began delaying decisions during a period of rising costs, the firm’s entire financial position became contingent on one relationship and one set of decisions it could not control.
For owner-operated service firms, client concentration is often the most significant single risk on the balance sheet. It compounds quietly while the relationship is healthy and becomes acute the moment it is not.
Why does it threaten your business’s resilience?
When one client represents a large share of your revenue, two things happen that compound each other. The first is revenue volatility: if that client reduces spend, delays payment, or ends the relationship, you face a cash shortfall with little warning. The second is a slow shift in bargaining power, because a client who knows they are critical to your survival will eventually use that fact.
eCapital UK, a specialist invoice finance provider, describes this plainly: clients who represent a large share of revenue gain bargaining power that tends to shift contract terms in their favour over time. Lower prices, extended payment schedules, additional scope for the same fee. The founder often does not notice this creep until they look at a client relationship that has grown in size and quietly shrunk in margin.
FreeAgent, whose accounting platform is widely used by UK small businesses, notes that losing a single key customer in a highly concentrated business can be far more damaging than in a diversified one, and that lenders and potential buyers can see this risk in the numbers before you have thought to mention it. If you are approaching a bank for a loan or talking to a potential acquirer, high concentration is one of the first things they will ask about.
This is why client concentration sits at the intersection of operational resilience and financial planning. It determines how vulnerable you are to a single bad conversation.
How much is too much?
There is no statutory UK threshold for SMEs, but commercial practice has converged on some working markers. UK lender 365 Finance describes 40% or more from one client as high concentration risk. Credit providers in sectors like logistics flag it from 25%. M&A advisers and invoice finance providers broadly treat anything above 20-25% for a single client as worth active planning and contingency thinking.
These are not legal limits. They are commercial norms that reflect how risk is priced rather than what is permitted. The practical breakdown, based on lender guidance and M&A advisory practice, looks like this:
- If your top client is above 40-50% of revenue, lenders treat this as very high risk. Buyers may discount valuations significantly or walk away from a deal entirely.
- If your top client sits between 25-40%, lenders flag it and expect evidence of a contingency plan.
- If your top three clients account for more than 60-70% of combined revenue, the business is fragile even if no single client appears dominant.
- Below 20-25% for the largest client, with the top five clients below 60% combined, is where finance providers generally view the client book as reasonably resilient.
eCapital UK gives the example of an IT services firm generating 60% of revenue from its top three clients, describing this as high client concentration and a significant financial risk. FOCUS Bankers, which advises on M&A transactions, has completed deals where concentration reached 85% in a single client, but notes that these consistently attract valuation discounts or deal conditions designed to account for the risk.
The numbers are a diagnostic, not a verdict. Knowing where you sit is the starting point.
When can you live with high concentration?
High client concentration is a risk you can choose to carry deliberately, under the right conditions. The key variables are contract structure, client stability, and your financial buffer. A client who represents 40% of your revenue on a five-year contract with minimum commitments and termination provisions is in a very different position from one generating the same share on rolling monthly terms with no notice period.
Some specialist firms choose to go deep with one or two anchor clients as a deliberate commercial strategy. A consultancy embedded in a single large organisation on a multi-year retainer, functioning as an outsourced department, may accept high concentration in exchange for predictable income and solid margin. In that context, the risk looks more like employment risk than business risk. You know it exists. The question is whether you are managing it actively.
Early-stage firms often have unavoidably high concentration in years one and two. That is usually how a business gets its foothold. The concentration becomes a problem if it is still there in year four or five without a plan to diversify as capacity grows.
Where concentration is structurally unavoidable, because the available client pool is simply small, the realistic mitigations shift to building cash reserves sufficient to cover three to six months of costs, cross-selling additional services to deepen the relationship, and keeping your team’s capabilities portable so they can move to new clients if the anchor relationship ends.
The honest test: is your current concentration a deliberate choice you have thought through, or is it an exposure you have not looked at? If it is the latter, that is worth changing before funding, an exit, or a change of circumstance at the client makes it urgent.
What should you track and do next?
The practical starting point is calculating three numbers: the percentage of revenue from your largest client, from your top three, and from your top five. If any single client sits above 25%, you have something worth thinking through. If your top three collectively exceed 60%, that warrants a conversation with your accountant or adviser about what a real contingency plan would look like.
Beyond client-side concentration, there is a parallel risk worth naming: your technology and supplier stack. Many service firms now depend heavily on a cloud CRM, an AI platform, or an outsourced IT function. Over-reliance on any single vendor creates a single point of failure that can disrupt delivery even when your client relationships are perfectly healthy.
The FCA’s cloud outsourcing guidance (FG16/5) requires regulated firms and, in practice, many of their suppliers to plan for what happens if a key provider fails. The NCSC’s Cyber Security Toolkit for Boards makes a related point about understanding key dependencies and planning for their loss. For a 5 to 50 person service firm, this translates into a straightforward question: what would you do if your primary platform was unavailable for a week?
The practical actions, in sequence: calculate your concentration numbers, review the contract terms on your largest client relationships, check whether your technology stack has a single-vendor dependency, and decide for each exposure whether it is a deliberate choice or an accident. If you are approaching any form of external funding, a business sale, or an honest review of your business’s financial position, your answers to these questions will matter before you expect them to. Better to know the answers first.
To work through what your concentration numbers look like and where to start, Book a conversation.
