Customer Concentration Risk: How to Price It

Customer concentration risk is what happens when one customer brings in too much of your revenue, and it is one of the fastest ways to lose money on a sale price, a loan, or the whole deal. There is no single legal line, but the pattern in how buyers and lenders actually behave is consistent: real unease starts around 15% of revenue tied to one account, serious pushback starts around 20-25%, and past 30% plenty of buyers will not bid at all. If you are selling, this is the first thing to fix. If you are buying, this is the first number you check, before you fall in love with the earnings.

What counts as customer concentration

Customer concentration is the share of your total revenue, or better, your gross profit, that comes from a single customer or a group of related customers - same ownership, same site, same contract that renews as one decision. Add up the top customer's billings for the last 12 months and divide by total revenue. That percentage is the number every buyer will ask for on day one of diligence.

There is an actual accounting line here, not just broker folklore. Under US GAAP's segment reporting rule, ASC 280, a public company has to separately disclose any single customer worth 10% or more of its revenue. Private trades businesses do not file with the SEC, but that 10% mark is where the rule came from, and it is why 10% is the first checkpoint most buyers glance at even on a business that will never see a 10-K.

Two traps people miss when they calculate this themselves:

• Related accounts count as one. Three "different" property management companies owned by the same investor are one customer for this purpose, not three.
• Revenue isn't the same as profit. A customer who is 25% of revenue but gets your deepest discount can matter less than a 15% customer billed at full rate. Buyers who know what they're doing check both.

How a buyer reprices a concentrated business

Take a $1,000,000-revenue trades business - a service company doing residential and light commercial work - where one general contractor sends 40% of the jobs. On paper, the seller's discretionary earnings might be $250,000, which on a clean, diversified business in this size range could reasonably sell in the 2.0x-2.5x SDE range. See our guide to valuation multiples by industry for how those bands get set.

The 40% account changes the conversation before the buyer even opens a spreadsheet. Here is roughly how that plays out:

1. The multiple gets cut. A buyer paying a full multiple on $250,000 of SDE is really betting that $100,000 of it (the GC's 40% share) survives a change of ownership. Many will simply strip that risk out of the headline price and renegotiate structure instead of walking away outright.
2. The structure shifts. Instead of a flat $550,000 purchase price, expect a lower cash number at close plus a holdback or an earnout tied to the GC's account actually renewing for 12-24 months post-close.
3. The lender gets nervous. SBA-backed lenders underwrite against the SBA's own Standard Operating Procedures for the 7(a) program, and a heavily concentrated customer base is exactly the kind of cash-flow risk that makes an underwriter ask harder questions, require a bigger seller note, or shrink the loan amount they're willing to put behind the deal.

None of that means the deal is dead. It means the price you see on a "comparable" sale with a diversified customer base is not the price you're actually going to get.

A buyer isn't pricing your revenue. They're pricing how much of your revenue survives the day one customer finds out you sold.

The thresholds buyers and lenders actually use

Ask five brokers where the real line sits and you'll get five different numbers, because there is no single official standard the way there is for, say, a GAAP disclosure rule. But the practitioner consensus clusters in a consistent pattern:

• Under 10%: barely registers. Every business has a biggest customer.
• 15-20%: questions start. Expect a specific line of diligence on that account's contract terms, tenure and margin.
• 20-30%: expect the offer, the structure, or both to change. This is where earnouts and holdbacks tied to that specific account become normal, not aggressive.
• Above 30%: a meaningful share of buyers decline to bid at all, especially strategic and private equity buyers who have a dozen other deals to look at instead.

BizBuySell's own guidance to buyers puts the underlying logic plainly: if the main customer walks after a change of ownership, the buyer has effectively paid for a customer relationship it never actually owned. That is the real risk under the percentage, not the percentage itself.

Rule I live by from running a maintenance company that worked for housing associations and letting agents: no single client gets to be the reason the lights stay on. If one account could end your month with a phone call, that account isn't a customer anymore. It's a boss you don't get paid enough to answer to.

It changes the deal, not just the price

Concentration rarely kills a deal outright at the quality end of the market. What it reliably does is change how the deal gets structured:

• Earnouts tied to the account. Part of the price pays out over one to two years, conditional on that specific customer's contract renewing.
• Holdbacks. A slice of the purchase price sits in escrow until the risk period passes.
• Bigger seller notes. If the lender shrinks the loan because of the concentration, the gap usually gets filled by you financing part of your own sale.
• Longer transition periods. The buyer wants you personally introducing them to that account, in person, for months, not a handover email.

Every one of those moves risk back onto the seller. That's exactly why fixing concentration before you list is worth more than negotiating around it after an offer is on the table.

If you're selling: fix it before you list

Concentration takes time to unwind, which is exactly why it belongs on the same 12-24 month runway as the rest of your pre-sale cleanup. See our full checklist for preparing a business for sale. The specific moves that actually move the number:

• Win two or three new accounts of meaningful size before you go to market. Diversifying the top line is slower than any paperwork fix, so start it earliest.
• Get the big account onto a real contract with a term and a notice period, instead of a handshake that renews month to month. A buyer will pay more for 40% of revenue locked in for two years than for 40% that could walk with 30 days' notice.
• Put someone other than you in front of that customer. If the relationship lives on your cell phone, it's not an asset the buyer can rely on. Move the day-to-day contact to a manager well before you sell.
• Keep the margin on that account honest. If you've been discounting your biggest customer to keep them happy, fix the pricing now, not during diligence when it looks like you're padding the numbers for sale.

If a 12-24 month runway isn't realistic for you, go to market anyway and price it in yourself. A seller who already knows the number and has a structure in mind - "I'll take a two-year earnout on the GC account" - keeps control of the negotiation. A seller who gets surprised by it in diligence just takes whatever the buyer offers.

If you're buying: how to underwrite the risk

Concentration is one of the specific items on our due diligence checklist for buying a business, and it deserves more than a glance at the top-line number. Before you price an offer:

• Check contract transferability. Does the big account's agreement survive a change of ownership automatically, or does it need the customer's consent? A contract that needs re-signing is a contract you don't actually have yet.
• Check tenure, not just size. A customer who has bought from this business for twelve years behaves differently than one the seller landed eight months ago. Ask how the relationship was won and whether it was price, service, or a personal friendship with the owner.
• Ask to meet the account, if the seller will allow it. A confidential conversation with the key contact at the big customer, late in diligence, tells you more than any spreadsheet. This is also one of the red flags worth checking before you buy a business - a seller who refuses to ever let you near that relationship is telling you something.
• Price the earnout, don't just accept it. If you're structuring part of the price around that account renewing, model what happens to your returns if it does not. If the deal only works assuming the biggest account stays, you haven't actually de-risked anything, you've just delayed finding out.

Concentration isn't automatically a reason to walk. A business with one big account on a long, sticky contract, run by a seller who's happy to structure around it, can still be a good buy at the right price. What kills deals is a seller who won't acknowledge the number is a problem, or a buyer who doesn't check it until the loan paperwork is already moving.

Whether you're pricing concentration out of an offer or trying to fix it before you sell, start with a real number. Get a free valuation and see where your business actually sits, or browse trades businesses for sale if you're underwriting your next deal. For the full picture on everything else buyers check, read our guide to how to buy a blue collar business.