Customer concentration risk when buying a business
Short answer
Customer concentration means a large share of revenue comes from a few customers. Measure it as the share of revenue from the largest customer, the top 5 and the top 10, over several years, and then look at what keeps those customers: contracts, notice periods, assignment terms and whose relationship it is. High concentration doesn't rule out a deal, but it raises risk for you and the lender, and is usually handled through price, a seller note, a holdback, or confirming the relationship before closing.
A business with one big customer is really two bets: the business, and that customer's loyalty to a new owner.
Why concentration matters more after a sale
A big customer that has bought from the same owner for years has a relationship with that owner, not with the business in the abstract. A sale is a natural moment for the customer to reconsider: their contact is leaving, the new owner is unknown, and competitors may hear about the change and call. That's why concentration that looked stable under the seller can become the main risk under the buyer. It doesn't mean big customers always leave; many stay happily. It means the relationship has to be transferred deliberately, and the deal priced for the chance that it isn't.
How to measure it
Illustrative example, not a real business
Revenue is $2,000,000. The largest customer bought $600,000 (30%). The top 5 bought $1,100,000 (55%). The top 10 bought $1,400,000 (70%). The largest customer's share has risen from 22% to 30% in three years.
Stress-test it
Remove the largest customer and work out what happens to earnings. Lost revenue usually takes most of its gross profit with it, while many costs stay. Then recompute debt coverage with the DSCR calculator.
What to check about each big customer
- Contract term, notice period, pricing and renewal.
- Assignment and change-of-control clauses.
- Whose relationship it is: the owner, a salesperson, or the business.
- How long they've been a customer, and order trend.
- Credit and payment history.
How to protect yourself
- Price that reflects the risk.
- A seller note so the seller shares the risk.
- An escrow or holdback where appropriate.
- Meeting the customer before closing, with the seller.
- Longer seller transition focused on the key accounts.
Questions to ask the top customers (with permission)
Late in diligence, with the seller's agreement and a careful script, a short conversation with the largest customers is the most useful concentration check there is. Keep it about continuity, not price:
- How long have you worked with the company, and what do you value most about the service?
- Who do you deal with day to day, and who would you call with a problem?
- Are there any changes coming in your own business (volume, suppliers, in-house plans) that would affect what you buy?
- Is the current agreement up for renewal or rebid soon?
- What would make you comfortable continuing with a new owner?
Listen for the name they mention. If it's the seller's, plan the transition around that relationship.
Worked example: what losing the top customer does to coverage
Illustrative example continued, not a real business
From the business above: $2,000,000 of revenue, the largest customer at $600,000. Gross margin is 35%, so that customer brings $210,000 of gross profit. EBITDA is $400,000 and annual debt service on the planned loan is $260,000, so coverage is $400,000 ÷ $260,000 = 1.54. If the customer leaves and the business cuts $40,000 of costs that served it (a driver, some overtime), EBITDA falls to $400,000 − $210,000 + $40,000 = $230,000, and coverage drops to $230,000 ÷ $260,000 = 0.88. The business could no longer pay its loan from earnings. That doesn't mean don't buy; it means price and structure the deal around the possibility, and find out how likely it is.
Ways buyers handle concentration
| Approach | How it helps | Watch for |
|---|---|---|
| Talk to the customer before closing | Tests loyalty and plans directly | Needs the seller's agreement and care with confidentiality |
| Lower price | Reflects the risk in what you pay | Seller may resist; show the coverage math |
| Seller note | Seller shares some risk through deferred payment | SBA rules on standby and repayment |
| Contingent payment | Price adjusts if the customer leaves | Seller earnouts are prohibited in SBA change-of-ownership loans |
| Signed customer contract or renewal | Locks in some revenue | Notice periods and assignment clauses |
| Less debt | Business can survive the loss | More of your equity at risk |
Measuring concentration properly
Look at the shares over at least three years and by month, not just last year. Measure gross profit by customer as well as revenue, since a big customer often buys at lower margins. Group related customers: several locations of one chain, or several properties managed by one firm, are one relationship. And check the direction: a top customer's share rising while total revenue is flat means the rest of the business is shrinking. If the business sells through distributors or platforms, the "customer" may be the channel, and that's concentration too.
When concentration is acceptable
Some concentration is normal and manageable: a long-standing customer with a multi-year contract, several decision-makers who know the business, a track record through past ownership or staff changes, and pricing that's fair to both sides. Concentration is most dangerous when the relationship is personal to the seller, the agreement can end on short notice, and the customer has easy alternatives. Score each large customer on those points. A business with one strong, contracted anchor customer can be a better buy than one with five fragile ones.
Red flags in concentrated businesses
- The top customer's share is rising while total revenue is flat: the rest of the business is shrinking.
- No written agreement, or one that can be cancelled on short notice.
- The relationship is the seller's personal one.
- The customer is consolidating suppliers or bringing work in-house.
- Pricing to the big customer has been cut in the last two years.
- The seller won't let you speak to them, even late in diligence.
Contract terms that decide whether a big customer stays
For each customer above a set share of revenue, read the contract, or confirm there isn't one. These clauses matter most:
| Clause | What to look for |
|---|---|
| Term and renewal | When it ends, and whether renewal is automatic |
| Termination for convenience | Whether the customer can leave on short notice for any reason |
| Assignment and change of control | Whether the customer must consent to a sale, in an asset or stock deal |
| Pricing | Fixed prices, caps on increases, or volume rebates |
| Exclusivity and volume | Whether they must buy from you, or simply may |
| Key person clauses | Whether the contract names the seller personally |
A customer with no contract can leave any day. That doesn't make it a bad deal, but the price and structure should assume it is possible.
Concentration among suppliers and staff
The same test applies on the other side of the business. Check how much of your purchases come from one supplier, and whether that supplier could change terms or stop selling to you. Check how much revenue depends on one employee's relationships. Concentration anywhere is a risk to price and plan for, not just among customers.
Frequently asked questions
What counts as high customer concentration?
There's no single rule. Buyers and lenders look harder whenever losing one customer would hurt the ability to pay the loan. Test it: remove the biggest customer and recompute earnings and debt coverage.
How do I check customer concentration?
Get revenue by customer for three years from the sales ledger or invoices, rank them, and compute the top 1, top 5 and top 10 share each year.
Can I talk to the big customers?
Usually only late in diligence and with the seller's permission, often jointly. Many buyers make it a condition before closing.
Can I use an earnout for concentration risk?
Not in an SBA-financed acquisition: SOP 50 10 8.1 prohibits earnouts. Seller notes, holdbacks and price are the usual tools there.
How do lenders treat customer concentration?
They look at it closely, because losing a big customer can break debt coverage. Under SBA SOP 50 10 8.1, a Quality of Earnings report (required at $3 million or more for initial acquisitions) must assess customer concentration. Below that, lenders still ask for revenue by customer and may require more equity or tighter terms when one customer dominates.
Should I avoid any business with a big customer?
Not necessarily. A long-standing customer with a contract, several contacts at the business and a history through past changes can be a stable anchor. Price and structure the deal for the risk, test what happens to debt coverage if they leave, and talk to them before closing if the seller agrees.
Sources
Related guides
General information, not legal, tax, financial or investment advice. Rules and lender practices change; check the linked sources and talk to your attorney, CPA and lender about your deal. Examples with named numbers are illustrations, not real businesses. OKtoBuy's Deal Check does not value businesses or give price opinions.