The 20% client rule: when one client is too big

Updated October 7, 2026 · 8 min read

The 20% client rule says no single client should account for more than 20% of your annual revenue. It is a rule of thumb, not a regulation, used by agency advisers, business buyers and lenders as the point where depending on one client becomes a real risk to profit, negotiating power and the value of the business.

Where the 20% number comes from

Nobody legislated 20%. It shows up independently in several places that look at the same risk:

• Agency advisers: Deborah Dawton, CEO of the UK Design Business Association, told Design Week that “a single client should account for no more than 15% to 20% of an agency’s income”.
• Business buyers: FOCUS Investment Banking writes that “any customer generating in excess of 20% of sales will catch the eye of a buyer and generate a detailed review”, that more buyers decline above 30%, and that valuation can be reduced “perhaps 20–35%”.
• Credit insurers: Allianz Trade defines high customer concentration as any single customer at 20% or more of revenue.
• Stricter versions: BizBuySell’s rule of thumb is 10% per customer, and US public companies must disclose any customer at 10% or more of revenue under ASC 280.

So 20% is the common upper line, with 10–15% as the comfortable zone. For the full set of thresholds, see customer concentration risk explained.

Why 20%: the profit math

Losing 20% of revenue rarely means losing 20% of profit. Service businesses carry fixed costs (salaries, rent, software) that do not leave with the client. Take an agency with these numbers:

A 20% revenue loss cuts profit by 80% in this example. At 30% the same business makes a loss of $30,000, and only cutting people closes the gap. That is why advisers put the line around 20%: below it, losing the largest client hurts; above it, it can threaten the business.

Check your largest client

Enter your clients and their revenue for the last twelve months. Nothing leaves your browser.

The cost you do not see on the P&L

A client above 20% knows it matters. It becomes harder to hold your price at renewal, to refuse scope creep, or to push back on a bad brief, because the downside of losing the account is so large. Many owners only notice this when they look back at how many concessions went to one client.

How firms keep clients under 20%

Grow the second tier first

Clients at 5–15% of revenue are the fastest way to a flatter book. More work for them costs less to win than a new client.

Review the large client’s pricing

If the largest account is on old rates, a price increase at renewal either improves margin or lowers its share. Either outcome reduces the risk.

Refer overflow

When a large client wants more than you want to depend on, a partner can take part of the work. You keep the relationship without adding to the concentration.

Protect what you cannot yet diversify

Notice periods of 60–90 days, longer terms, more than one contact inside the client, and a cash buffer sized to the client’s monthly revenue buy time if the relationship ends.

Already over 20%? A 90-day plan

1. Measure it properly: trailing twelve months, related entities combined, pass-through costs removed.
2. Calculate the gap: client revenue ÷ 0.2 = the total revenue you need. The difference from today is your new-business target.
3. Secure the account: check renewal date, notice period and termination terms, and propose improvements at the next renewal.
4. Pick two or three mid-sized clients to grow and one new industry to win clients in.
5. Re-measure every quarter and watch the direction, not only the level.

When the rule is too strict

Early freelancers and new firms often cannot stay under 20%: with three clients, someone is at least a third of revenue. Some businesses also sell at good prices with high concentration, when the relationship is long, contracted and profitable. FOCUS notes it has sold manufacturing businesses with customer concentration as high as 85% at a premium multiple. The rule is a direction, not a pass or fail: know your number, stop it rising, and protect the account until the list grows.

Frequently asked questions