A founder I worked with was celebrating €10,000 in monthly revenue. She was spending €12,000 a month to generate it. She was losing €2,000 every month and didn’t realize it because nobody had taught her to look at the right numbers.
Unit economics is the most skipped topic in entrepreneurship education, and it’s the one that determines whether your business survives or slowly bleeds to death. The good news: it’s simpler than everyone makes it sound. You need three numbers. That’s it. Three numbers tell you whether your business model works.
If math makes your eyes glaze over, stay with me. I’m going to explain this the way I wish someone had explained it to me before I spent a year running a business that looked like it was growing but was actually dying.
The Three Numbers
Here they are. Every business decision you make should be traceable to one of these.
Number 1: Customer Acquisition Cost (CAC)
How much does it cost you to get one new customer?
Total up everything you spend to get customers in a month: ad spend, marketing tools, the value of your time spent on sales and marketing (yes, your time has a cost), any commissions or referral fees. Divide that total by the number of new customers you got that month.
Example: You spent €500 on ads, €200 on marketing tools, and 40 hours on sales at a value of €30/hour (€1,200). Total: €1,900. You got 20 new customers. CAC = €1,900 ÷ 20 = €95.
It costs you €95 to get one customer.
Number 2: Average Revenue Per Customer (ARPC)
How much does one customer pay you over their entire relationship with your business?
For a one-time purchase business, this is the average order value. For a subscription, it’s the monthly price times the average number of months a customer stays.
Example: You charge €39/month. The average customer stays for 7 months before canceling. ARPC = €39 × 7 = €273.
Each customer generates €273 in revenue over their lifetime.
Number 3: Cost to Serve (CTS)
How much does it cost you to deliver the product or service to one customer?
This includes hosting costs, support time, materials, tools, and any per-customer expense. For digital products, this is often very low. For services, it can be significant.
Example: Your hosting costs €0.50 per customer per month. You spend an average of 15 minutes per customer per month on support at €30/hour (€7.50). CTS per month = €8. Over 7 months (average customer lifetime): €56.
It costs you €56 to serve one customer over their lifetime.
The Equation That Determines Everything
Now combine the three numbers:
Profit per customer = ARPC - CAC - CTS
Using our example: €273 - €95 - €56 = €122 profit per customer.
That’s it. That’s unit economics. If this number is positive, your business model works at the unit level. If it’s negative, every new customer costs you money — and growing faster just means dying faster.
The founder I mentioned at the beginning? Her CAC was €120, her ARPC was €89, and her CTS was €15. Profit per customer: €89 - €120 - €15 = negative €46. She was paying €46 for the privilege of serving each customer. No amount of growth fixes negative unit economics. More customers just means more negative €46s.
This connects to the three numbers framework I talk about frequently. Understanding these numbers isn’t optional — it’s the difference between a business and a charity.
Making the Numbers Better
If your unit economics are negative or barely positive, you have exactly three levers to pull.
Lever 1: Reduce CAC.
- Find cheaper acquisition channels. If you’re spending €50 per customer on Facebook ads, try organic content or community posts that might bring customers for €5-10 each.
- Improve conversion rates. If your landing page converts at 1%, improving to 2% cuts your CAC in half with the same ad spend.
- Build referral loops. Customers who bring other customers have a CAC of nearly zero.
- Focus on one channel and master it rather than spreading budget across many channels.
Lever 2: Increase ARPC.
- Raise prices. This is usually the fastest lever. Most founders are underpriced.
- Increase retention. If your average customer stays 7 months, getting them to stay 10 months increases ARPC by 43%.
- Upsell and cross-sell. Offer premium tiers, add-ons, or complementary products.
- Reduce churn. Fix whatever is causing customers to leave. Sometimes it’s a product issue. Sometimes it’s an expectations mismatch set during marketing.
Lever 3: Reduce CTS.
- Automate manual processes. If you’re spending 15 minutes per customer on support, a FAQ page or help documentation might reduce that to 5 minutes.
- Reduce infrastructure costs. Switch to cheaper hosting, tools, or service providers.
- Improve product quality to reduce support needs. The best way to reduce support cost is to build a product that doesn’t need support.
The order matters: most founders should pull lever 2 first (raise prices), then lever 1 (find cheaper channels), then lever 3 (reduce costs). Price increases are the fastest and highest-impact change. Cost reduction is the slowest and lowest-impact change.
Unit Economics for Different Business Models
The three numbers apply to every business, but the specifics vary by model.
Digital products (courses, templates, ebooks):
- CAC: Usually moderate (content marketing, paid ads)
- ARPC: One-time purchase price (or bundle price)
- CTS: Very low (hosting, delivery platform fees)
- Typical target: CAC should be less than 30% of ARPC
SaaS (subscription software):
- CAC: Varies widely (free trial to enterprise sales)
- ARPC: Monthly price × average lifetime in months
- CTS: Hosting, support, development amortization
- Typical target: ARPC should be at least 3x CAC (the “LTV:CAC ratio”)
Services (consulting, coaching, freelancing):
- CAC: Usually low (referrals, networking, content)
- ARPC: Project fee or monthly retainer × average engagement length
- CTS: Primarily your time (the biggest cost)
- Typical target: Bill at least 3x your cost to serve
Physical products (e-commerce):
- CAC: Varies (marketplace fees, paid ads, influencer marketing)
- ARPC: Average order value × average purchase frequency
- CTS: Cost of goods sold + shipping + returns
- Typical target: At least 50% gross margin (ARPC - CTS) / ARPC
These targets aren’t absolute. But if your numbers are far below these benchmarks, your model has a structural problem that won’t be solved by growing faster.
The Dashboard You Need
I keep a monthly unit economics dashboard. Here’s the template.
| Month | New Customers | Total Revenue | Marketing Spend | Time Spent (hrs) | CAC | ARPC | CTS | Profit/Customer |
|---|---|---|---|---|---|---|---|---|
| Jan | 15 | €1,200 | €300 | 20 | €60 | €80 | €12 | €8 |
| Feb | 22 | €1,800 | €400 | 25 | €52 | €82 | €11 | €19 |
| Mar | 28 | €2,400 | €500 | 30 | €54 | €86 | €10 | €22 |
The trends matter more than the absolutes. If CAC is trending down and ARPC is trending up, you’re heading in the right direction. If both are moving the wrong way, you have a problem regardless of the current numbers.
I review this monthly. Not weekly (too noisy) and not quarterly (too slow to catch problems). Monthly gives you enough data to see patterns without drowning in statistical noise.
Notice that I include time spent as a cost, valued at a reasonable hourly rate. If you don’t count your time, your unit economics look artificially good. Your time is your most valuable resource — don’t pretend it’s free.
When Unit Economics Kill an Idea
Sometimes the numbers tell you the business model doesn’t work. This is painful but valuable information.
Example 1: The coaching business that doesn’t scale.
CAC: €50 (content + referrals). ARPC: €500 (5 sessions at €100). CTS: €300 (5 hours of your time at €60/hour). Profit: €150 per customer. To make €100,000/year, you need 667 customers. At 5 sessions each, that’s 3,335 coaching hours. Plus sales time. You physically cannot do this.
The unit economics work per customer but fail at the business level because CTS includes your time and your time doesn’t scale. The fix: group coaching (reduces CTS per customer), a course (eliminates per-customer time), or raising prices significantly.
Example 2: The marketplace with thin margins.
CAC: €30 (paid ads). ARPC: €8 per transaction × 4 transactions per year = €32. CTS: €5 per transaction × 4 = €20. Profit: €32 - €30 - €20 = negative €18 per customer per year. The marketplace takes a small cut of each transaction, but customer lifetime value doesn’t cover acquisition cost.
The fix: increase transaction volume (get customers to transact more often), increase take rate (charge more per transaction), or reduce CAC dramatically (perhaps through organic/viral growth rather than paid ads).
When the numbers clearly don’t work, killing the idea isn’t failure — it’s intelligence. Better to discover negative unit economics in month 3 than in month 18.
Key Takeaways
- Three numbers determine your business viability: Customer Acquisition Cost (CAC), Average Revenue Per Customer (ARPC), and Cost to Serve (CTS). Profit per customer = ARPC - CAC - CTS.
- If profit per customer is negative, growing faster makes you die faster. Fix the unit economics before scaling.
- Pull levers in this order: raise prices first (fastest impact), then reduce acquisition costs, then reduce service costs.
- Track unit economics monthly in a simple dashboard. Trends matter more than absolutes.
- Count your time as a cost. If you don’t, your unit economics are fiction. Your time is your most expensive resource.
