Same scene every month: the ad budget is on the table and everyone has a feeling. “I think it's working.” “I think it's expensive.” But this isn't a question of feeling — it's arithmetic. And the answer lives in three numbers: CAC, LTV, payback.
The trio came out of the startup world, but it does its best work in service businesses: courses, clinics, studios, consultancies, membership businesses… Because in these businesses the customer doesn't buy once and leave — they stay for months. And a customer who stays changes the math completely.
CAC — what does one customer cost you?
Customer Acquisition Cost: take everything you spent on marketing in a month — ads, agency, content, tools — and divide it by the number of new customers you won that month. That's it. The subtlety: count the total cost of acquiring the customer, not just ad spend. An undercounted CAC is the one number that always flatters itself.
LTV — what does that customer leave you in total?
Lifetime Value: take the gross profit a customer leaves you per month, and multiply by how many months they stay on average. Calculate it on profit, not revenue — what's left after rent, instructor costs, materials. A business that doesn't know its LTV can't know what “expensive” means in advertising: a 1,500-lira CAC is a disaster for a customer who leaves 2,000 — and a bargain for one who leaves 7,000.
Payback — how many months until the money comes back?
Payback period: divide CAC by the gross profit the customer leaves per month. The result is how long it takes the money you gave to ads to come back into the till. For an SMB managing cash flow this is the most vital of the three — LTV promises a future on paper, payback talks to this month's rent. The SaaS norm is under 12 months; in a service business running on monthly cash, you want it far shorter.
| Line | Value | How it's derived |
|---|---|---|
| Monthly marketing cost | ₺60,000 | Ads + agency + tools |
| New customers / month | 40 | From the CRM |
| CAC | ₺1,500 | 60,000 ÷ 40 |
| Gross profit per customer / month | ₺600 | Fee − variable cost |
| Average customer lifetime | 12 months | From membership data |
| LTV | ₺7,200 | 600 × 12 |
| LTV : CAC | 4.8 : 1 | 7,200 ÷ 1,500 |
| Payback | 2.5 months | 1,500 ÷ 600 |
How to read the ratio
The industry's reference point is the threshold David Skok of Matrix Partners has argued for years: in a sustainable subscription/membership model, LTV should be at least 3× CAC — and well-run companies cruise above 5×. Around one-to-one means you're buying every customer with cash and paying for the shipping on top.
LTV:CAC tells you whether the model is right; payback tells you how long your cash is tied up. Look at both before you decide.
The decision in one table
Once you have the three numbers, the budget decision collapses into four cases. Whichever box you're in, the move is known:
| Situation | Diagnosis | Move |
|---|---|---|
| High LTV · low CAC | The machine works | Scale budget in steps, hold the ratios |
| High LTV · high CAC | Good model, inefficient channel | Test targeting, creative and the landing — push CAC down |
| Low LTV · low CAC | Cheap to acquire, hard to keep | Work pricing, packaging and retention — grow LTV |
| Low LTV · high CAC | Ads are widening the hole | Pause the budget; fix the funnel and the offer first |
These numbers can't live in a spreadsheet
The hard part isn't the formula, it's the data. CAC needs spend, LTV needs how many months customers stay, payback needs monthly profit — collected continuously and correctly. In a spreadsheet, the table looks great for two months; in month three someone forgets to update it. That's why our approach never changes: the numbers should come from the system — ads panel, CRM and revenue on one screen, the table updating itself. Half of what we call growth management is installing exactly this discipline.
If you want one owner who runs the campaigns, reads the numbers, and pushes CAC down and LTV up with a weekly experiment — the page where we explain growth management is here.
GO TO THE GROWTH PAGE→