Why One Big Client Could Be Quietly Costing You Money

If more than half your revenue comes from a single customer, you might call that a success story.

A big win. A stable relationship. A business that’s landed a major account. A buyer sees it differently. To them, it’s a risk.

The “Eggs in One Basket” Problem

It’s the classic “don’t put all your eggs in one basket” problem, and it applies just as much to a business as it does to an investment portfolio. Ask yourself one question: if that one client left, would your business survive?

If the honest answer is “not easily,” a buyer has to price that risk in. They will offer you less than they’d offer for an identical business with the same revenue spread across twenty clients instead of one. Same turnover. Same profit margin. Same team. Different price tag — purely because of where the money comes from.

This isn’t a hypothetical. Buyers see concentrated customer bases fail constantly, and they build that experience into every offer they make.

How Buyers Actually Price the Risk

Most buyers value a business as a multiple of its profit — say, four or five times annual earnings. That multiple reflects how confident the buyer feels about future income continuing after they take over.

A business with revenue spread across twenty clients gives a buyer real confidence. Lose one client, and the business barely notices. The other nineteen keep the numbers steady.

A business built around one dominant client tells a different story. Lose that client, and revenue doesn’t dip — it collapses. Buyers know this, so they discount the price to compensate. Sometimes they build in an earn-out instead, making a chunk of the purchase price conditional on that big client staying put for a year or two after completion. Either way, concentration costs you money on the day you sell.

Why This Happens Even to Good Businesses

Customer concentration rarely happens by accident. It happens because the business is good at what it does. A capable, reliable supplier attracts bigger and bigger orders from a client who trusts them. Growth feels effortless, because it’s coming from a relationship that already works.

The trouble is, that same strength becomes a structural weakness. The better you serve one client, the more your business quietly reorganises itself around their needs — their deadlines, their specifications, their way of working. Over time, walking away from that client doesn’t just cost you revenue. It can mean unwinding processes, staffing decisions, and even parts of your product or service that only exist because of them.

None of this is a reason to feel bad about landing a big account. It’s simply a reason to treat the growth that follows differently than you might otherwise.

This Isn’t a Reason to Turn Away a Big Client

To be clear: none of this means you should turn down a big client, or deliberately limit how much business you do with them. A large, stable account is genuinely valuable — for cash flow, for credibility, for the confidence it gives your own team.

The real lesson is different. It’s a reason to actively build a broader base alongside that client, not instead of them. That way, no single relationship — however good — has the power to make or break the business.

Think of it as insurance you build in parallel, not a trade-off you make instead.

What Broadening Your Base Actually Looks Like

Diversifying a customer base doesn’t happen overnight, and it rarely happens by accident either. A few practical steps make the biggest difference:

Set a target. Decide what maximum percentage any single client should represent — many advisers suggest capping any one customer at around 15–20% of total revenue — and track it, not just once a year, but as part of regular management reporting.

Invest in business development even while things feel comfortable. It’s tempting to ease off on sales and marketing when one client is keeping you busy. Resist that. The quiet periods are exactly when you should be building the pipeline that protects you later.

Diversify by sector as well as by client. If your smaller accounts are all in the same industry as your big one, a downturn in that sector can hurt you almost as much as losing the big client outright.

Formalise the big relationship where you can. Longer contracts, notice periods, and renewal terms all give you visibility and time to react, rather than losing the account overnight.

The More Spread Out, the More a Buyer Will Pay

The more spread out your customer base becomes, the more confidently a buyer can predict your future income. And the more confident they feel, the more they’ll pay for that confidence.

This works in a very direct, almost mechanical way. Buyers build financial models projecting your revenue forward, usually three to five years. A concentrated customer base makes every year of that model uncertain, because so much depends on one relationship continuing exactly as it has. A diversified base makes the model far more reliable — and buyers pay a premium for reliability, every time.

It’s worth remembering this works both ways. If you’re already thinking about a sale in the next few years, this is one of the highest-leverage changes you can make. Reducing concentration even modestly, well before you go to market, can move the needle on your eventual sale price more than almost any other single action.

When to Start Thinking About This

The earlier you address customer concentration, the more options you have. Diversifying your customer base takes time — new clients need to be won, relationships need to mature, and revenue needs a few years of history behind it before a buyer will fully trust it.

That’s why this is squarely a “two to three years before you plan to sell” issue, not a “fix it during due diligence” issue. A buyer’s team will ask for a customer revenue breakdown early in any deal process. There’s no way to disguise concentration once someone is looking for it, and trying to obscure it only damages trust at exactly the point you need it most.

The Bottom Line

One big client can feel like security. But to a buyer, it often looks like risk. A diversified customer base is worth real money on the day you sell — so spread the base before that day comes.

How H&Hendricks Can Help

An honest look at customer concentration, and a plan to broaden the base before a buyer ever sees it, is part of H&Hendricks’ Building Value service.

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Ashley Bancroft is a founding Partner of H&Hendricks. A qualified Chartered Accountant and specialises in finance, strategy and entrepreneurship, with particular focus on value creation.