How to Calculate What You Can Afford to Pay for a Customer

Before asking whether an advertising campaign is working, you first have to define what “working” actually means. Defining that requires a single mathematical baseline that almost no executive has committed to paper: how much you can afford to pay for one new acquired customer.

The Math, in Four Lines

Start with gross margin, never top-line revenue. If you sell a product or service for one thousand euros and your cost of goods sold is six hundred, your gross margin is four hundred. Next, determine how many times an acquired customer buys across the entire lifecycle of the commercial relationship: if they transact an average of three times, total customer lifetime gross margin is twelve hundred euros.

From that sum, deduct what it costs to deliver ongoing service, and decide what portion of that net margin you are prepared to invest to acquire them. Allocating one-third is a common benchmark, not an immutable law: it depends on how rapidly you need payback and how much cash reserves you hold. At one-third, in this scenario, you can comfortably afford to pay up to four hundred euros to acquire a single net-new customer.

Why This Number Changes Everything

Without this number, campaigns are evaluated purely on gut instinct—and executive instinct invariably tilts in one direction: everything feels excessively expensive. A cost per lead of forty euros sounds alarming in a vacuum. But if one out of every five leads converts into a paying customer, that customer costs you two hundred euros to acquire. When that customer generates four hundred euros in margin, the question ceases to be “is this too expensive?” and becomes “why aren’t we buying ten times as many?”

Almost every paid media campaign I have seen prematurely killed was pulled by someone who had never done this arithmetic. The leads were costing less than the business could comfortably afford, yet they felt overpriced.

The Two Most Common Mistakes

Calculating against revenue rather than gross margin. An acquisition cost equal to 20% of topline revenue can represent a runaway success or an operational catastrophe depending on your product margins—and you cannot distinguish between the two scenarios by looking at revenue alone.

Accounting solely for the initial purchase. If your typical client transacts repeatedly and you omit that recurring value from your model, you are conceding a massive advantage to any rival who ran the numbers correctly. That rival can afford to pay three times what you pay for the exact same prospect. You did not lose because their creative was superior: they defeated you with basic arithmetic.

How to Apply It in Practice

This figure becomes your non-negotiable operational threshold. Above it, an ad set is paused or restructured. Below it, you scale budget aggressively until the margin threshold is met. This is not a leisurely topic for an end-of-month board meeting: it is a weekly operational decision. To make it, customer acquisition cost must be transparently visible to you in real time—not hidden behind agency reports.

And if your business lacks historical tracking to compute this accurately (common with lengthy B2B sales cycles), the only honest approach is stating that reality before any contract is signed, rather than fabricating a mathematical model around an arbitrary guess and calling it a measurement.