One client paying most of the bills is a concentration risk

How it happens without a decision

Nobody sets out to depend on one buyer. A good client asks for more work, the work is enjoyable and the payments are reliable, and because they are absorbing most of the available hours there’s no capacity to look for anybody else.

A year later they represent the majority of revenue, and the position was never chosen. It accumulated one reasonable decision at a time, which is why it is so common among businesses that are otherwise run carefully.

The obvious risk and the less obvious ones

The obvious risk is that they leave, and the damage is proportional to the share they represent. What is less discussed is that they usually leave for reasons entirely unconnected to your work — a change of budget, a reorganisation, a new person in the role who has their own suppliers.

The subtler cost is what dependence does to your judgement while they are still there. Terms that would be refused from anybody else get accepted. Late payment goes unchallenged. Scope expands without repricing, because raising it feels dangerous.

That is the real expense of concentration, and it’s being paid continuously rather than at the end. The relationship becomes one where only one party can afford to be difficult.

The classification question

There is a further consideration that varies enormously by country and is worth understanding rather than ignoring. Many jurisdictions have rules about when an arrangement is genuinely a business-to-business supply and when it more closely resembles something else, and those rules often look at exactly the features a dominant client relationship tends to have — one main source of income, work done at their direction, on their premises, on their equipment, over a long unbroken period.

The consequences differ, and so do the tests. This is not something to reason about from general principles or from what somebody in another country reported. If a single client provides most of your income over a sustained period, ask a qualified accountant in your own jurisdiction what that means for you, because the answer affects both parties and is easier to address early.

Reducing it takes longer than people expect

The instinctive plan is to find another client of similar size, which is difficult precisely because there is no spare capacity to look. The realistic route is slower: keep a small amount of selling running continuously, take on smaller work alongside the large client even when it’s inconvenient, and accept that the mix improves over quarters rather than weeks.

Where the dominant client is an organisation rather than a person, spreading relationships within it helps a little. Work commissioned by several departments is less fragile than work commissioned by one individual who might leave, though it remains one buyer as far as the risk is concerned.

When the concentration is deliberate

Sometimes it’s a rational choice. A large, stable client can offer efficiencies a scattered client base cannot — no repeated selling, deep familiarity, a predictable schedule — and some people build a good working life around exactly that.

The condition that makes it defensible is honesty about what it is. Held deliberately, it comes with preparation: a larger reserve, a pipeline kept warm even when unnecessary, a clear view of what the first six months without them would look like. Held by default, it comes with none of that, which is what turns an ordinary business event into a crisis.

What to watch for

The signals that a dominant relationship is ending are usually visible before it happens. A slower pace of new work. A new person in the decision-making role. Longer approval times. Payments taking a little longer than they used to. A restructure anywhere near the department you work with.

None of those is conclusive and all of them justify quiet activity elsewhere. The worst position to be in is discovering the relationship has ended on the same day you start looking for its replacement, and that is a position entirely within your control to avoid.

Two further habits make the exposure easier to live with. Keep your own copies of anything you would need to demonstrate the work later, since a portfolio built inside somebody else’s systems can become inaccessible the day the relationship ends. And keep a small number of other relationships warm — the previous client you finished with on good terms, the contact who asked about availability last year. Neither takes much time, and both shorten the gap considerably if it comes.