Is your biggest client really your best one?

In almost every SME, there's one client that generates a significant share of revenue — 15%, 20%, sometimes 30%. They get the most attention, the most flexibility, the most availability. They're considered the "best client."

But high revenue doesn't automatically mean high margin. In many cases, the biggest client also has the most aggressive commercial terms: significant discounts, tight delivery deadlines, extended payment terms, customization requests, frequent after-sales support.

When you add up all these hidden costs, the real contribution margin can be very different from the perceived one.

How do you discover the real margin per client?

The analysis requires going beyond revenue and looking at the actual costs associated with each client. The steps are:

1. Calculate net revenue. Gross revenue minus discounts, allowances, credit notes. The "official" revenue often doesn't match what's actually collected.

2. Calculate variable costs per client. Sum the variable costs of all products sold to that client, weighted by actual quantities. If a client mostly buys low-margin products, the mix matters more than volume.

3. Add client-specific costs. These are expenses incurred only for that client:

Dedicated transport or rush deliveries
Special packaging
Extra technical or after-sales support
Dedicated sales time (visits, negotiations, complaint handling)
Financial cost of extended payment terms (a client paying at 120 days costs more than one paying at 30)

4. Calculate the contribution margin per client. Net revenue – variable costs – specific costs = real margin.

An example that changes perspective

A manufacturing company with €3.5M in revenue has two main clients:

	Client Alpha	Client Beta
Annual revenue	€ 700,000	€ 350,000
Discounts and allowances	– € 70,000 (10%)	– € 10,500 (3%)
Net revenue	€ 630,000	€ 339,500
Product variable costs	€ 455,000	€ 210,000
Dedicated transport	€ 18,000	€ 5,000
Extra support	€ 12,000	€ 2,000
Financial cost (120 days)	€ 15,000	€ 0 (pays at 30 days)
Total costs	€ 500,000	€ 217,000
Contribution margin	€ 130,000 (18.6%)	€ 122,500 (36.1%)

Client Alpha bills twice as much, but the margin percentage is half. In absolute terms, the gap is minimal: €130,000 versus €122,500. Client Beta, with half the revenue, generates nearly the same margin — and without the financial costs of late payments.

If the company decided to grant an additional 5% discount to Client Alpha to "not lose them," the margin would drop to €98,500 — less than what Client Beta generates.

Why does this happen, and what to do about it?

Large clients tend to get better terms over time: growing discounts, extra services, payment flexibility. Each individual concession seems small, but the cumulative effect can be significant.

This doesn't mean large clients should be dropped. It means they should be managed with awareness:

Renegotiate terms — if the margin is too low, it's legitimate to revisit prices or payment conditions. A client yielding 25% is better than one yielding 10%
Reduce client-specific costs — standardize deliveries, eliminate non-contracted services, streamline support
Diversify the client portfolio — dependence on a single client is a risk beyond just margin. If the main client hits trouble, the impact on the business is disproportionate
Set a minimum margin threshold — just as with discounts, clients also need a floor below which you won't go

The link to revenue that grows but doesn't pay

This analysis explains a very common phenomenon: revenue grows but profit doesn't. If growth is driven by high-volume, low-margin clients, the company works more without earning more.

The contribution margin per client is the tool that makes this imbalance visible. It doesn't replace the commercial relationship — it enriches it with information that allows you to negotiate from a more informed position.

Where to start

You don't need to analyze every client. The top 10 by revenue — those that together represent 60-80% of the total — are enough. For each:

Calculate net revenue (after discounts and allowances)
Estimate associated variable costs (from the full cost of products sold)
Add specific costs (transport, support, financial cost)
Calculate the contribution margin

The result is a ranking of clients by real margin — often very different from the ranking by revenue. It's one of the numbers to monitor regularly for making data-driven commercial decisions.

A fractional controller can build this analysis and update it periodically, without the cost of a dedicated internal resource.

The price list guide explores how to translate per-client margin analysis into a price list that protects profitability.

Want to discover how much your main clients really contribute? Get in touch for a no-commitment conversation, or learn about our strategic consulting.