Client concentration risk: when one client is too much of your agency

Client concentration risk is the share of an agency's revenue that would disappear if its largest clients left. As a working rule, the largest client above 15 to 20% of revenue, or the top five above 50%, is a flag worth acting on, and above 30% for one client it changes what a buyer will pay. The fix is rarely to fire the client: it is to grow everything else, reprice and ring-fence the big account, and lengthen the contract's notice period over 12 to 18 months.

This guide uses one fictional agency throughout: 22 people, $200,000 of contracted monthly revenue across 12 clients, an 18% net margin, and one client, Client A, worth $68,000 a month. That client is 34% of the agency.

How do you measure client concentration?

Use contracted revenue for the trailing 12 months, not hours times rate and not a single month. A retainer that paid $68,000 a month is $816,000 of revenue for the year, whatever the team logged against it. Pass-through costs such as media spend come out of both the numerator and the denominator, because a $50,000 ad budget you pass through is not $50,000 of agency revenue.

Then report three ratios and one index.

The top client share is the number most people quote, and it is the one a buyer asks for first. The top five share catches the agency with no single giant but four clients at 15% each, which is just as exposed to one industry downturn or one procurement team.

What does the concentration index tell you that the percentages do not?

The index is the same arithmetic economists use for market concentration, borrowed for a client list. Take each client's share as a percentage, square it, and add the squares. Client A at 34% contributes 1,156 on its own. The other eleven clients together add 456. The total is 1,612.

The plain-language reading is the effective number of clients: divide 10,000 by the index. This agency has 12 clients on paper, but its revenue behaves as if it had 6.2 equally sized ones. Twelve clients of equal size would score 833 and behave like twelve.

Rough bands that hold up in practice:

• Under 1,000: diversified. Losing any one client hurts but does not change the plan.
• 1,000 to 1,800: moderate. One or two accounts set the year.
• Above 1,800: concentrated. The same line antitrust regulators use for a highly concentrated market, and a fair marker for an agency whose fortunes belong to one or two clients.

The index earns its place when the shape of the book changes. Adding a new $5,000 client barely moves the top client percentage, but it shows up in the index, and the effective number of clients is a figure an owner and a finance lead both understand without a lecture.

What thresholds do buyers and advisors use?

There is no regulation behind these lines. They are the rules of thumb that come up repeatedly in agency M&A advice, lender conversations and due diligence checklists, and they are consistent enough to plan against.

For the top five, under 40% is comfortable, 40 to 50% is normal for an agency under $3 million, and above 50% is the flag. Small agencies run more concentrated than large ones by arithmetic alone: a $1.2 million agency with eight clients has an average client of 12.5%, so a 20% top client is barely above average. Judge the number against your size, then plan to bring it down as you grow.

The marketing agency valuation calculator applies this logic directly. The discount starts once the largest client passes 15%, reaches about 6% at 25%, 10% at 30% and 18% at 40%, and the top five share adds up to another 12%, with the two capped at 35% together.

What does concentration actually cost?

Four costs, and only the last one shows up at sale time.

Pricing power. The client that is a third of your revenue knows it, or its procurement team does. Every renewal conversation happens with the agency negotiating against its own payroll. Agencies in this position tend to accept scope additions without a change order, because the alternative feels unaffordable.

A team built around one account. At 34%, Client A has roughly seven people who work mostly on it. Their skills, schedule and habits fit that client. Hiring decisions get made for that client's roadmap, and the department looks fully utilized for reasons that vanish with one email. See agency utilization and capacity planning for how a single account distorts the hiring triggers.

Cash shock. This is the one that hurts first. Here is the agency the month after Client A gives 30 days' notice.

Revenue falls 34% overnight. Payroll does not, because nobody is let go the same day, and overhead does not move for months. The agency goes from $36,000 of monthly profit to a $32,000 monthly loss, and even after it cuts the seven-person team it sits at 8.7% net, well under the 15 to 25% target, with a smaller book carrying the same rent and leadership. If Client A also paid on net 60 terms, about $136,000 of receivables are outstanding with a client that has just decided to leave.

Valuation. Run the example agency through the calculator: $2.4 million of revenue, $432,000 of adjusted EBITDA (18%), $602,000 of SDE, 85% recurring, 10% growth, eight years in business. With Client A at 34% and the top five at 68.5%, concentration takes about 21% off the multiple: 2.29 times SDE, a midpoint near $1.38 million. The same agency with an 18% largest client and the top five at 52.5% values at about 2.74 times, near $1.65 million, roughly $270,000 more. Structure moves too: the calculator expects about 66% of the price at close in the first case and 77% in the second, with the rest held back until the big client renews under the new owner. How marketing agencies are valued walks through the rest of the multiple.

What is the hidden version of concentration risk?

The big client is often the least profitable one. Size buys it attention, senior time, discounts and a team that says yes. Measure margin per client from contracted revenue and absorbed labor cost, as client profitability for marketing agencies lays out, and compare the giant to the rest of the book.

Client A is 34% of revenue but only about 26% of gross profit, and at 36% margin it sits under the 40% floor the rest of the site uses as the line for a problem account. The other eleven clients run at 54%, inside the healthy 50 to 60% range. The concentration is real, but it is concentration of revenue and payroll more than of profit.

That changes the plan. An owner who sees only the 34% wants to protect the account at any cost. An owner who sees the 36% margin knows the account has room to be repriced, and that losing it would hurt less than the revenue line suggests, as long as the team around it shrinks with it. Watch the servicing gap on the big account in particular: discounts and free scope tend to collect where the agency feels least able to say no.

How do you dilute a big client without firing it?

Four moves, run together over 12 to 18 months.

Grow the rest of the book. This does most of the work and takes longest. For the example agency it means one new client of $12,000 to $14,000 a month most quarters, plus expansion of two or three existing accounts. Point new-business effort at clients who would each land in the 5 to 10% range, not at the next giant.

Review the big client's price and scope. Raising the price on the largest client raises its share of revenue, which looks backwards. Do it anyway when the margin is under 40%. Concentration of profit is what decides how badly the agency hurts if the client leaves, and a repriced account at a healthy margin is a smaller risk than a discounted one at the same share. Pair the increase with trimming scope that the retainer never funded. How to price agency retainers covers the repricing conversation.

Ring-fence the team. Put the people who serve the big client into a defined pod with its own capacity plan, so its cost is visible and it does not quietly absorb the agency's best people. A pod that is sized to the account scales down with it. A team spread across every client turns a lost account into idle time everywhere.

Change the contract terms at renewal. Ask for a 90-day notice period instead of 30, net 30 payment instead of net 60, and a minimum term of 12 months. Each month of notice is $68,000 of revenue paying for the transition instead of a $32,000 month of loss. These terms cost the client little, and a client who values the work usually agrees.

What does an 18-month plan look like?

Here is the example agency, quarter by quarter. Client A is repriced 6% at its renewal in the second quarter, from $68,000 to $72,000, with scope trimmed so its margin rises from 36% to 42%. Everything else is new and expanded business.

After six quarters the agency has 17 clients. The top five share falls from 68.5% to 54.5%, the concentration index from 1,612 to 1,034, and the effective number of clients from 6.2 to 9.7. Client A's share of gross profit, at $30,240 out of $146,880, is about 21%.

Be honest about the pace. The rest of the book grew 64% in 18 months to get here, and Client A is still above 20% of revenue. Dilution is slow arithmetic, which is why the contract terms matter: they cut the damage of a loss now, while the growth cuts the share later. Track the same measures each quarter against the benchmarks in marketing agency KPIs and benchmarks.

When is concentration acceptable?

Some agencies carry a large client on purpose: an anchor account that funds a new office, a new service line or the first senior hires. That is a legitimate strategy if the concentration is protected. A large client is a deliberate anchor rather than a risk when most of these hold:

• A written term of 12 months or more, with a notice period of 90 days or longer.
• A gross margin at or above the rest of the book, not a discount bought with size.
• Several stakeholders and budgets inside the client, so one champion leaving does not end it.
• A ring-fenced team whose cost would come down with the account.
• A rising rest of book, so the share falls each year even while the account grows.

Separate divisions of one parent company help, but count them as one client for concentration. A single procurement review or change of CMO reaches all of them at once.

Even a protected anchor belongs under about 40%. Above that, a buyer is valuing the contract rather than the agency, and the owner is running a single-client business with extra steps.

What to do this month

• Pull 12 months of contracted revenue by client, with pass-through removed.
• Calculate the top client, top three and top five shares, and the concentration index.
• Measure gross margin for the largest client against the rest of the book.
• Check the big client's notice period, payment terms and renewal date.
• If the largest client is above 20%, write the quarter-by-quarter table above for your own agency, with a new-business target for each quarter.
• Put the repricing and the contract terms on the agenda for the next renewal, not the one after.

Verbial shows contracted revenue and gross margin per client from absorbed labor cost, with utilization by person and department, so the share and the margin of your largest account sit on one page each month. The valuation calculator shows what the same share does to the multiple.