What is customer concentration?

Caleb Hinton

10 June, 2026

Customer concentration is the share of your turnover that depends on your biggest customers. In other words, it is not simply how many customers you have, but how evenly your revenue is spread across them. A company with 50 customers can still have high customer concentration if one buyer accounts for a large part of sales, while a business with fewer customers may be less concentrated if no single account dominates. That matters for UK SMEs in particular: at the start of 2025 there were 5.7 million private sector businesses in the UK, 5.64 million of them small businesses, and SMEs made up 99.85% of the business population.

Key Takeaways

Customer concentration is a revenue and cash flow risk in one. If a single customer accounts for 10% or more of turnover, their late payment, lost contract, renegotiated pricing, or closure/liquidation can destabilise the whole business. With late payments costing the UK economy £11 billion a year, the risk is very real.
Lenders notice it – Higher customer concentration is linked to higher loan interest rates, more restrictive covenants, and shorter loan terms. In a UK lending environment where SME finance approval rates are already below pre-pandemic levels, a concentrated revenue base makes securing funding harder.
The fix starts with sales strategy – Winning customers in adjacent segments, spreading exposure across sectors and regions, and tightening payment terms are the most effective ways to reduce concentration, finance can buy breathing space, but it cannot substitute for a more diversified customer base.

Customer concentration explained

Customer concentration is related to risk.

The clearest way to think about customer concentration is dependency. If one customer leaves, pays late, reduces orders or renegotiates pricing, how much damage does that do to your revenue and cash flow? Would your business be in trouble if one client left?

The IFRS treats a customer contributing 10% or more of revenue as a “major customer” for disclosure purposes, which is one reason the 10% mark is widely seen as a meaningful early warning signal, even though it is not a universal lending rule.

Customer concentration is not linear

Customer concentration is often discussed as single-customer exposure, but the same risk can show up in other ways. If most of your revenue comes from one industry, such as construction or hospitality, or from one region, your business can still be concentrated even if you invoice lots of separate firms. The Prudential Regulation Authority defines concentration risk as losses caused by imperfect diversification and specifically points to single-name, sector and geographical concentration.

Customer concentration is always relevant

This is not just a problem for large corporates. Smaller firms are often more exposed because they begin with a handful of anchor accounts and build from there. In a market where most UK businesses are small, customer concentration is one of the simplest ways to judge resilience: the broader the revenue base, the less likely one account can destabilise the business.

Why customer concentration matters

Research consistently shows that firms with more concentrated customer bases are exposed to higher risk. An NBER paper found that smaller firms and firms with a more concentrated customer base display higher volatility. Academic work also finds that a more concentrated customer base is associated with a higher cost of equity and debt, while another study shows that higher customer concentration increases bank loan spreads, increases restrictive covenants and shortens loan maturity. In plain English, relying too heavily on a few customers can make your business look riskier to fund.

Cash flow problems with customer concentration

Customer concentration is dangerous because revenue risk quickly turns into cash-flow risk. Official UK research published for the Small Business Commissioner says late payments cost the UK economy almost £11 billion a year, affect over 1.5 million businesses, leave firms owed an estimated £26 billion at any given time and contribute to 14,000 business closures each year. The government said in May 2026 that late payments close 38 businesses every day. If a large share of your turnover sits with one slow-paying account, the impact is far more severe than if the same overdue balance were spread across a wider customer base.

Defensive actions

The same late-payments research found that 22% of affected businesses spent staff time chasing unpaid debtors, 14% injected personal funds into the business, 6% took out debt finance and 6% reduced headcount as a result of late payments. Those figures show why lenders pay attention to concentration: when one or two customers have too much influence over incoming cash, the business may need emergency measures just to stay liquid.

How to measure customer concentration

The simplest measure is top customer share. Take the revenue from your biggest customer over the last 12 months, divide it by total revenue, then multiply by 100. If your largest customer generated £120,000 and your turnover was £600,000, your top customer share is 20%. That single figure tells you how exposed you are to losing, repricing or delaying payment from your largest account. The 10% IFRS major-customer threshold gives useful context for deciding when that figure has become material.

Your top 5 customers

Top customer share is useful, but it does not tell the whole story. A business might have no single dominant customer, while still depending on a very small group. That is why many lenders, investors and finance teams also review the share of revenue earned from the top three or top five customers. If your top five clients account for most of your turnover, the underlying risk is still concentration risk, even if your largest individual account looks acceptable on its own. Research into customer concentration and corporate risk-taking also uses sales to the top five customers as a key measure of dependency.

Weighted concentration measure

For larger or more data-driven businesses, a weighted measure such as the Herfindahl-Hirschman Index can be useful. The PRA uses HHI as a concentration risk measure and defines it as the sum of the squares of relative portfolio shares. A lower HHI suggests a more diversified book; a higher HHI points to a more concentrated one. You do not need to use HHI to understand customer concentration, but it is helpful when you want a more precise view of how evenly revenue is distributed across customers, sectors or regions.

What lenders usually want to see

No serious lender should assess your business on one concentration number in isolation. Sector, margins, contract length, customer quality, payment history, order visibility and overall affordability all matter as well. Even academic evidence shows that not all concentration is equal: one study found that suppliers with concentrated bases of safer government customers had a lower cost of equity than other concentrated profiles. That said, heavy exposure to one customer is still a clear warning sign because it leaves too much resting on a single decision-maker.

Why diversified revenue supports finance applications

The credit market tends to price customer concentration as a real risk, not a theoretical one. Campello and Gao found that higher customer concentration leads to higher interest rate spreads and more restrictive bank-loan terms. In the current UK finance market, smaller businesses already face a selective environment: British Business Bank reporting said the success rate for SME finance applications in the period from 23Q1 to 24Q2 was 56%, still below the 74% seen in 18Q1 to 19Q2, while 19% of businesses open to finance for growth thought it would be difficult to secure it. A wider and more diverse customer book helps show lenders that your income is more resilient.

What a healthy profile usually looks like

A stronger profile usually means no single customer can disrupt payroll, tax payments, supplier commitments or debt repayments on its own. It also means exposure is spread across more than one industry or location, debtor days are under control and customer relationships are backed by contracts, repeat orders or recurring revenue where possible. Customer concentration does not have to be zero; it simply needs to be manageable. The question a lender is really asking is whether the business can absorb a shock without falling into distress.

How to reduce customer concentration

Reducing customer concentration usually starts with sales strategy rather than finance. The most effective move is to win more customers in adjacent segments that already fit your offer, rather than chasing completely unrelated work. That might mean targeting smaller businesses if you currently rely on a few large accounts, or moving into a neighbouring vertical where your case studies and pricing still make sense. If broadening your customer base is part of a wider expansion plan, Rise Funding’s guide to top business growth strategies in 2026 is a useful next read.

Spread risk across sectors and regions

If your customer list looks diverse on paper but most revenue still comes from one trade or one location, the next step is to diversify demand sources. That matters because concentration risk is not limited to named customers; sector and geographic dependence can create the same problem. Rise Funding’s guide to business growth is relevant here too, because market expansion, operational improvement and new channels all help reduce reliance on one pocket of demand.

Strengthen terms, contracts and credit control

Diversification takes time, so businesses also need to protect themselves while they widen their customer base. Long-term contracts, staged invoicing, deposits, tighter payment terms, credit checks and faster collections all reduce the damage if a major customer slows down. That matters because official research shows businesses often respond to late payment by chasing debtors, injecting personal funds or taking out extra finance, which is exactly the kind of pressure a well-run credit-control process is meant to avoid.

Use funding to support diversification

Finance can help create breathing space while you diversify, but it should not be used to pretend concentration risk does not exist. Short-term funding may support stock purchases, payroll or working capital while you win new accounts, yet the underlying issue still needs fixing. The goal is to use finance to buy time for better diversification, stronger cash flow and a more resilient revenue mix, not to remain permanently dependent on one or two customers.

Final thoughts

Customer concentration is one of the simplest ways to assess how resilient a business really is. If too much turnover comes from one customer, one sector or one region, the company is more exposed to delayed payments, renegotiated prices, lost contracts and tougher funding terms. The practical answer is to monitor your top customer share, top five share and sector mix regularly, then act before concentration becomes a barrier to growth. For lenders, investors and business owners alike, a broader and more diverse customer base is usually a sign of stronger cash flow, lower risk and a healthier business.

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