There's one piece of math most owners never run: what percentage of your revenue depends on a single client.
It's an uncomfortable number, which is exactly why it gets skipped. But buyers, lenders, and investors are already running it on your business, whether you have or not. Here's where the danger lines sit, what one client's exit can do to a company in a matter of weeks, and a 20-minute test to find out if you're one phone call away from a crisis.
How much revenue from one customer is too much?
There are hard lines where customer concentration starts costing you real money. According to a May 2026 customer concentration analysis from Beancount.io:
- Under 10% of revenue from any single customer is the healthy zone.
- 10% to 20% is caution territory. Private equity firms typically draw a hard internal line at 15%.
- Above 30%, businesses see their valuation drop 20% to 35% compared to a similarly sized, diversified competitor.
This isn't a soft guideline. It's a number that shows up directly on a term sheet, a loan application, or a sale price, whether you've ever calculated it yourself or not.
Your bank already knows your concentration number
In asset-based lending, banks typically advance 80% to 85% against eligible receivables, but cap any single customer at 15% to 25% of the total borrowing base. Revenue above that threshold from a concentrated customer can be excluded from your collateral entirely (Beancount.io, May 2026).
If a bank won't fully count your biggest client's revenue as real collateral, take that seriously. It's an outside opinion on how stable that revenue actually is.
Federal contractors just got a live demonstration
In 2024, 65,500 small business contractors received a combined $155 billion in federal payments. During a government shutdown, roughly $3 billion a week in contractor payments freezes, and unlike furloughed federal employees, contractors don't receive back pay (U.S. Chamber of Commerce analysis of Bloomberg Government data, October 2025).
For a contractor whose revenue leans heavily on one agency, a shutdown isn't a headline. It's an immediate, unpaid pause on most of their income.
Your best client could also be your biggest liability
A few years ago I sat with a consulting client in an African country, working through his client list to understand who actually paid his bills. When we got to the government contracts, I asked what percentage of his revenue they represented.
Seventy percent, he said.
I asked him if providing for his family was something he took real pride in. Of course, he said. Then I told him that if the government ever shifted that work to a competitor, it would likely kill his business.
Ten seconds of silence. I never heard from him again after that call.
I don't think he was upset with me. I think I said out loud the sentence his own numbers had been trying to tell him for years, and nobody had ever said it to him plainly before.
Concentration is not stability
Seventy percent from one source isn't unusual. It's actually one of the most common ways small businesses grow. One relationship gets big, it becomes easy, and easy starts to look like stable.
But concentration and stability are not the same thing. A client that makes up most of your revenue isn't your biggest asset. It behaves exactly like your biggest single point of failure: everything is fine until the day it isn't, and then everything is not fine all at once.
Why losing a 70% client usually ends the business
The math is unforgiving. If one customer is 70% of your revenue, losing them doesn't shrink your business by 70%. It usually ends it.
The fixed costs you built to serve that client (staff, equipment, leases) don't shrink along with the revenue. They stay exactly the same size while the income that covered them disappears overnight.
The verdict: what Cellares' layoffs teach about concentration risk
The decision: In late August 2026, cell therapy manufacturing startup Cellares lost its largest customer when Bristol Myers Squibb ended a roughly $380 million partnership. BMS had determined that Cellares' automated manufacturing platform couldn't meet the requirements to produce commercial batches of its CAR-T therapy Breyanzi. Within a week, Cellares cut 100 jobs. A week after that, it cut 68 more. That's 168 employees gone in under a month.
My verdict: Losing the BMS deal wasn't the real mistake. Building a company where losing one deal could cost 168 jobs in three weeks was.
Why most people read it wrong: The headline reads like a manufacturing failure. The real story is a concentration failure. One customer relationship had grown large enough that its exit didn't just hurt Cellares. It forced an immediate, public restructuring of the entire company.
Your version: You don't have a $380 million contract on the line. But you might have the small business version of the exact same setup: one client whose exit would force you to lay off half your team in the same month. The dollar amount is different. The math is identical.
How to find out if you're one client away from a crisis: a 5-step test
You don't need a valuation firm to run this test. You need your last twelve months of invoices and about twenty minutes.
- Calculate your real number. Add up revenue from your single largest client over the last twelve months and divide by total revenue. Most owners have never actually done this math. They've only felt it.
- Know the zones. Under 10% from one client is healthy. 10% to 20% puts you in caution territory. Above 30% is a red flag serious enough that buyers, lenders, and investors will discount your business for it, and they're not wrong to.
- Strip out the fixed costs tied to that client. Staff, equipment, space, software: whatever exists mainly to serve that one relationship. That number is your actual exposure if they leave.
- Build one new relationship before you need it. The fastest way to bring a 70% number down isn't firing your big client. It's adding smaller ones next to it until the percentage shrinks on its own.
- Put this number on a recurring calendar, not a one-time fire drill. Concentration creeps up quietly, the same way it did for the client I described above. Nobody decides on purpose to become dependent on one account.
This week's move
Calculate what percentage of your revenue came from your single largest client over the last twelve months. If the number surprises you, that's exactly the point. It means you've been running on a fact you never actually looked at.
Related reading: if you're not sure your revenue numbers are telling the truth, start with Are You Making Decisions With Bad Numbers?. If cash is already tight, read Why Can't You Pay Yourself This Month? And if a big decision about that client keeps getting pushed off, see The Interest You're Paying on Every Decision You Won't Make.
Order The Brown Box
The Brown Box: How to Fix What's Broken in Your Business Before It Breaks You is out now, and Reduce Risks is chapter four of the TURNAROUND method for exactly this reason. Customer concentration is one of the quietest risks a business carries, because it looks like success right up until it doesn't. That chapter walks through how to spot it before it spots you. Order now on Amazon or learn more about the book.
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Worried one client is carrying too much of your business? Get in touch.