Most arguments about marketing spend are really arguments about a number nobody in the room has worked out. Someone says the advertising is expensive. Someone else says it is working. Both are talking about cost, and neither is talking about what a customer is worth. Until you know that, every budget conversation is a matter of taste.
Start with contribution, not revenue
Take an average order or an average contract and subtract what it costs you to deliver it. Materials, the hours of whoever does the work, the commission if there is one. What is left is the contribution: the money that stays with the business from one sale. Revenue is the number owners quote and contribution is the number that pays the rent, and on some services the two are far enough apart to reverse a decision.
Then count the second purchase, and the third
Look at your customers from last year and ask how many bought again. Not a feeling, a count. Multiply your contribution by the average number of purchases a customer makes before they stop, and you have what one customer is worth over the life of the relationship.
This is where most businesses discover something they half knew. A first sale that looks barely worth having can be comfortably profitable by the third, and a first sale that looks excellent can be the only one that ever happens.
Only now look at what you pay to acquire one
Add up everything you spent last month on getting new customers. Advertising, the agency, the time your team spent on it. Divide it by the number of new customers you actually won, not the number of enquiries you received. That is your acquisition cost.
Set it beside the worth of a customer. The gap between the two is the only marketing metric that survives contact with a bank statement.
What the number changes
It changes what you are willing to pay for an enquiry, which changes which channels are affordable. It changes how hard it is worth working to keep a customer, because keeping one costs a fraction of finding one. And it changes how you read a slow month, because a month with fewer sales but better ones is not the same as a bad month.
None of this requires a new system. It requires an afternoon with your own invoices. If the number surprises you, that is the point: you were making decisions without it.
Where it usually goes wrong
Two mistakes. Using revenue instead of contribution, which flatters everything and hides the services that lose money at volume. And counting enquiries as customers, which makes acquisition cost look far lower than it is and quietly rewards the channel that sends the most people who never buy.