A founder was celebrating. She had just crossed EUR 10,000 in monthly revenue. Ten months of work, finally paying off. She wanted to reinvest in Facebook ads to grow faster.
I asked her three questions. How much does it cost to acquire a customer? How much does a customer spend over their lifetime? What is the margin on each sale?
She did not know any of them. Not approximately. Not roughly. She had no idea.
We ran the numbers together. Customer acquisition cost: EUR 47. Average customer lifetime value: EUR 52. Gross margin: 60%.
She was making EUR 5.20 per customer. Before rent. Before tools. Before her own salary. She was growing revenue while losing money — the fastest path to an impressive-looking bankruptcy.
Three numbers. If you know them, you can make every business decision with clarity. If you do not know them, you are driving at night with the headlights off.
Number 1: Customer Acquisition Cost (CAC)
CAC is the total cost of acquiring one new customer. Not the cost of one ad click. The total cost — including every euro spent on marketing, every hour of sales time, every tool subscription that supports the acquisition process.
The formula: CAC = Total acquisition spending / Number of new customers acquired in the same period.
If you spent EUR 2,000 on marketing last month and acquired 40 new customers, your CAC is EUR 50.
But most founders undercount the spending. Include:
- Ad spend
- Tools (email marketing, landing page builders, analytics)
- Your time spent on marketing and sales (value it at what you would pay someone else to do it)
- Freelancer costs for design, copywriting, or content
- Platform fees and commissions
For Vulpine Creations, our CAC was roughly EUR 12. Low, because most of our customers came through organic channels — watering hole communities, word of mouth, and content. We invested time rather than money, but even time has a cost.
Benchmarks: For digital products sold directly, a CAC under EUR 30 is healthy. For SaaS, CAC under three months of subscription revenue is the rule of thumb. For services, CAC under 15% of the first engagement value.
Number 2: Customer Lifetime Value (LTV)
LTV is the total revenue a single customer generates over their entire relationship with your business.
For a one-time purchase business: LTV = Average order value x Average number of purchases per customer.
If your average order is EUR 65 and customers buy an average of 2.3 times, your LTV is EUR 149.50.
For a subscription business: LTV = Monthly revenue per customer x Average customer lifespan in months.
If customers pay EUR 29/month and stay for an average of 8 months, your LTV is EUR 232.
LTV is harder to calculate than CAC because it requires historical data. If you are just starting, estimate conservatively. Assume customers buy once. If they buy again, that is upside.
The critical ratio: LTV to CAC. Your LTV must be at least three times your CAC for a sustainable business. If your LTV is EUR 150 and your CAC is EUR 50, your ratio is 3:1 — the minimum viable ratio. If your LTV is EUR 150 and your CAC is EUR 100, your ratio is 1.5:1 — you are in trouble.
Below 3:1, you do not have enough margin to cover operations, product development, and your own salary after paying for customer acquisition. The business looks like it is growing but it is actually bleeding.
Number 3: Gross Margin
Gross margin is the percentage of revenue that remains after subtracting the direct cost of delivering the product or service.
The formula: Gross Margin = (Revenue - Cost of Goods Sold) / Revenue x 100.
If you sell a digital course for EUR 100 and the delivery costs (platform hosting, payment processing fees, support time) are EUR 15, your gross margin is 85%.
If you sell a physical product for EUR 50 and the product cost, packaging, and shipping total EUR 25, your gross margin is 50%.
What counts as cost of goods sold:
- Materials and manufacturing
- Payment processing fees (typically 2.5-3.5%)
- Platform fees (Gumroad takes 10%, Shopify has monthly fees)
- Shipping and handling
- Direct labor for delivery (time spent per customer)
- Support costs attributable to the product
What does not count:
- Marketing (that is in CAC)
- Rent and overhead
- Your salary
- Tools not directly related to delivery
Benchmarks: Digital products should have 70-90% gross margins. Physical products: 40-60%. Services: 50-70%. Below these ranges, the business model needs restructuring.
Putting the Three Numbers Together
Here is the equation that determines whether your business is viable:
(LTV x Gross Margin) - CAC = Contribution per customer
If LTV is EUR 150, gross margin is 80%, and CAC is EUR 50: (150 x 0.80) - 50 = EUR 70 per customer.
That EUR 70 pays for your rent, tools, salary, and growth. If you acquire 100 customers per month, you have EUR 7,000 per month to run the business.
Now let’s run the struggling founder’s numbers: (52 x 0.60) - 47 = EUR -15.80 per customer.
She was losing money on every customer she acquired. Growing faster would have accelerated the losses. The Facebook ads she wanted to buy would have been accelerant on a fire.
Fixing Broken Unit Economics
If your numbers do not work, there are exactly four levers to pull.
Lever 1: Reduce CAC. Switch from paid acquisition to organic channels. Build content. Map your watering holes and invest time in community presence. Ask happy customers for referrals. Organic acquisition is slower but dramatically cheaper.
Lever 2: Increase LTV. Add products or services that existing customers can buy. Create upsells, cross-sells, or higher-tier offerings. Improve retention (for subscription businesses). Build your revenue engine with multiple paths to repeat purchase.
Lever 3: Increase price. Most first-time founders are underpriced. Raising the price by 20% with no other changes instantly improves both LTV and gross margin. If the conversion rate drops less than 20%, you come out ahead.
Lever 4: Reduce cost of delivery. Automate what you do manually. Switch from manual processes to systems where the volume justifies it. Renegotiate supplier costs as your volume grows.
Pull one lever at a time. Measure the impact. Then pull the next.
When to Calculate (and How Often)
First calculation: As soon as you have 20-30 customers. Below that, the sample is too small and the numbers are noisy.
Ongoing cadence: Monthly for the first year. Quarterly after that. The numbers change as you grow — your CAC might increase as you exhaust easy organic channels, your LTV might increase as you add products, your margins might shift as you scale.
The dashboard: I use a simple spreadsheet with three cells — CAC, LTV, Margin — updated monthly. Nothing more. The one number that matters most is the contribution per customer, calculated from these three.
The Discipline of Numbers
Most founders avoid unit economics because the numbers might tell them something they do not want to hear. A business that feels successful — growing revenue, happy customers, increasing activity — might be economically broken at the unit level.
But knowing the truth early is always cheaper than discovering it late. The founder who learns at EUR 10K/month that her unit economics are broken can fix it. The founder who learns at EUR 100K/month that her unit economics are broken has a crisis.
Financial discipline starts with knowing three numbers. Just three. How much does it cost to get a customer? How much does that customer spend? How much of that spend is profit?
If you do not know these numbers, find them today. If you do know them and they are healthy, you have a real business. If you know them and they are broken, you have a real problem — and now you can fix it.
Three numbers. Everything else follows.
