The owner is on a call with her agency. They share a slide. Impressions up 40%. Click-through rate strong. Cost per lead down to €4.
She nods. She has no idea if she made any money.
That's the whole problem in one meeting. Med spa owners get handed the numbers that look good and never see the ones that decide whether the ads actually work. So here are the five that matter — and the two your agency probably isn't showing you.
The five numbers, fast
Before the definitions, here's the map. Keep it next to any report someone sends you.
| Metric | Plain meaning | Real example (a med spa we run) | | --- | --- | --- | | CPL — cost per lead | What you pay for one person to raise their hand | €3.21 per lead | | ROAS — return on ad spend | Revenue ÷ ad spend | 71× (about €44,000 back on €620) | | CAC — customer acquisition cost | Ad spend ÷ paying clients won | about €7 per client (€620 ÷ 88) | | LTV — lifetime value | What a client is worth over all their visits | memberships + repeat treatments, months of revenue | | AEO — answer engine optimization | Getting recommended inside AI answers | cited by ChatGPT, Perplexity, Google AI Overviews |
Two of these — CPL and ROAS — are what agencies love to show. Two of them — CAC and LTV — are what actually tell you if the business grows. The fifth, AEO, is the one that barely existed two years ago and now quietly decides who gets found. Let's take them one at a time.
What is CPL, and why is it the shallow one?
CPL, or cost per lead, is what you pay for one person to raise their hand — fill out the form, request the consult. If you spend €300 and get 100 form fills, your CPL is €3.
It's the number everyone leads with because it's easy to make look good. Widen the targeting, dangle a freebie, and CPL drops. But a cheap lead that never books is worth exactly nothing. We've audited accounts with a gorgeous €2 cost per lead where almost no one showed up, because the ad attracted browsers hunting a discount, not people ready to book a treatment. CPL is a useful early signal. It is not proof you made money. Cost per booked client is.
What is ROAS, and when does it lie?
ROAS, or return on ad spend, is revenue divided by ad spend. Spend €1,000, make €5,000, and your ROAS is 5×. It's the closest of the easy metrics to the truth, because at least it points at revenue.
But ROAS lies the second the revenue isn't really tracked. If the "revenue" is estimated from form fills instead of tied to actual bookings, the number is fiction. Med spa benchmark surveys call 3–5× a "good" ROAS — but those averages are built from mostly-broken setups: boosted posts, no follow-up, likes counted as wins. One med spa we run hit 71× ROAS on a small, tightly-tracked budget, which tells you the survey average is a setup problem, not a limit. A high ROAS on untracked revenue is a story. A modest ROAS you can trace to real bookings is worth more.
What is CAC, and why does it matter more than CPL?
CAC, or customer acquisition cost, is what you pay in ads to win one paying client — total ad spend divided by clients, not leads. This is the first number on the list that pays rent.
Here's why it beats CPL. A lead isn't money. A client is. You can have a €3 cost per lead and still bleed cash if only one in fifty books. CAC ignores the vanity and counts the outcome. The med spa above spent about €620 and won 88 clients — that's roughly €7 to acquire a paying client. Now you have something real to judge, because you can hold it against what a client is actually worth. Which is the number nobody shows you.
What is LTV, and why is it the one most owners never see?
LTV, or lifetime value, is what a client is worth across every visit — not the first booking. And in a med spa, that's the whole game, because med spa revenue is repeat revenue. Memberships. Treatment series. Seasonal packages. The friend they refer. A first appointment that looks like €200 can be worth thousands over a year or two.
LTV matters because it sets your ceiling. If a client is worth €2,000 to you over time and costs €7 to acquire, you are not spending too much on ads — you're spending too little. Owners who only look at the first sale get scared of their ad budget and starve the thing that grows them. The spa across town that knows its LTV outbids them for the same client and wins. This is the number that quietly separates the practices that scale from the ones that plateau. If this is you — reports full of clicks, no clue on CAC or LTV — book a free audit and we'll put real numbers on it.
What is AEO, and why does it belong on this list now?
AEO, or answer engine optimization, is getting your med spa recommended inside AI answers — when someone asks ChatGPT, Perplexity, or Google's AI Overview for the best clinic in their city or how a treatment works. Think of it as SEO's newer cousin, aimed at the box that answers before anyone clicks a link.
It's on this list because search is changing under everyone's feet. More questions now get answered by an AI summary at the top of the page, and if you're not the source it cites, you're invisible in that moment — no matter how good your ad is. You earn AEO the boring way: clear pages that answer one real question at a time, third-party mentions of your business, and the same accurate name, address, and description everywhere online. No trick. Just being the most quotable answer in your market. We break down the traffic side of this in our post on the customers AI is already sending you that your analytics can't see.
How the five fit together
One line ties them up. CPL tells you if leads are cheap. ROAS tells you if a campaign paid back. CAC against LTV tells you if the business can grow. And AEO decides whether you get found in the first place.
Your agency will lead with the first two because they're easy to make pretty. The last three are where the money and the future live. When someone sends you a report, don't ask "how are the impressions?" Ask two questions instead: what did it cost to win a client, and what is that client worth to us? If they can't answer, you're not looking at marketing. You're looking at a slide.
The 30-Second Audit
Three yes/no questions. Answer them about your last marketing report.
- Can your agency tell you your CAC — what it actually cost to win a paying client, not a lead?
- Do you know your LTV — what a client is worth to you over a year, not one visit?
- Does your business show up when someone asks an AI for the best med spa in your area?
If any answer was no, book a free audit — we'll pull your numbers and tell you exactly what's broken, even if you don't end up working with us.
Impressions don't pay rent. Clients do. Learn the two numbers that tell them apart.