Unit Economics That Hold Up
The Hook
A business can look like it is winning, growing fast, raising money, making noise, while quietly losing money on every single customer. Unit economics is the lens that catches this before it becomes a disaster. Once you can run these numbers, you can tell a real business from an expensive illusion.
Plain English
Unit economics zooms all the way in to a single customer and asks one question: do we make money on each one, or lose it? Three numbers tell the story. CAC (customer acquisition cost) is what it costs you, on average, to win one new customer, including marketing and sales. ARPU (average revenue per user) is how much revenue one customer brings in over a chosen period, usually per month or per year. LTV (customer lifetime value) is the total profit you expect from one customer over their entire relationship with you, from first purchase to last. The whole game is the relationship between what you pay to get a customer (CAC) and what that customer is worth to you (LTV). If a customer is worth far more than they cost to acquire, the business has a real engine. If they cost more than they are worth, growth just digs the hole faster. This is why two companies with identical revenue can have completely different futures.
The Math
The headline number is the LTV to CAC ratio: lifetime value divided by acquisition cost. A common healthy benchmark is roughly 3 to 1, meaning each customer is worth about three times what you paid to win them. Below 1 to 1, you lose money on every customer and growth makes it worse. The second number to watch is the payback period: how many months it takes to earn back the CAC.
- ARPU = total revenue in a period / number of customers in that period
- LTV = (ARPU x gross margin percentage) x average number of periods a customer stays
- LTV to CAC ratio = LTV / CAC (roughly 3 to 1 is a common healthy target)
- CAC payback period (months) = CAC / (monthly ARPU x gross margin percentage)
A subscription business charges 50 dollars a month, so monthly ARPU is 50 dollars. Its gross margin is 80 percent, meaning 40 dollars of each monthly payment is actual profit (50 x 0.80 = 40). The average customer stays 24 months. So LTV = 40 dollars profit per month x 24 months = 960 dollars. It costs 300 dollars in marketing and sales to win each customer, so CAC is 300 dollars. The LTV to CAC ratio = 960 / 300 = 3.2 to 1. That sits right at the healthy benchmark: each customer is worth about three times what they cost to acquire. This is a business with a working engine.
Now a company that looks impressive from the outside. It charges 30 dollars a month (ARPU 30 dollars) at a 50 percent gross margin, so profit per month is 15 dollars (30 x 0.50). But customers only stay 6 months on average. LTV = 15 dollars x 6 months = 90 dollars. Meanwhile it spends heavily on ads and sales, so CAC is 200 dollars. LTV to CAC ratio = 90 / 200 = 0.45 to 1, far below 1. Every customer it wins costs 200 dollars and returns only 90 dollars of profit, a loss of 110 dollars each. The faster this company grows, the more money it burns. Revenue charts can look thrilling while the unit economics quietly guarantee failure.
Using the healthy business from Example 1: CAC is 300 dollars and each customer delivers 40 dollars of profit per month (50 dollar ARPU at 80 percent margin). The CAC payback period = 300 / 40 = 7.5 months. So it takes about seven and a half months before a new customer has paid back what it cost to acquire them, and everything after that is profit. Payback period matters because it tells you how long your cash is tied up before a customer turns positive. A short payback means you can reinvest in growth quickly. A long one means you need deep pockets to fund the gap, even when the LTV to CAC ratio looks fine on paper.
The Lingo
- CAC (customer acquisition cost)
- The average cost to win one new customer, including marketing and sales spend.
- ARPU (average revenue per user)
- The average revenue one customer generates in a chosen period, such as per month or per year.
- LTV (customer lifetime value)
- The total profit you expect from one customer over the whole relationship, from first purchase to last.
- LTV to CAC ratio
- Lifetime value divided by acquisition cost. Roughly 3 to 1 is a common sign of a healthy business.
- Payback period
- How long it takes to earn back the cost of acquiring a customer. Shorter frees up cash to grow faster.
- Churn
- The rate at which customers leave. Higher churn shortens the relationship and lowers LTV.
- Gross margin
- The percentage of revenue left after direct costs. It turns revenue per customer into actual profit per customer.
Practice
In the Room
The Trap
Judging a business by its revenue or growth rate while ignoring whether it makes money per customer. Fast growth on broken unit economics is not success, it is accelerating a loss. The second, subtler trap is staring only at the LTV to CAC ratio and forgetting the payback period: a business can have a healthy 3 to 1 ratio and still run out of cash if it waits a year to earn back each customer. Always check both. The questions that expose the truth: do we make money on a single customer, and how long until we get our acquisition cost back?
Quick Check
Q1.What does the LTV to CAC ratio tell you?
Q2.A customer is worth 960 dollars in lifetime profit and costs 300 dollars to acquire. What is the LTV to CAC ratio, and is it healthy?
Q3.Why can a fast-growing company still be in serious trouble?
Q4.ARPU is 50 dollars a month at an 80 percent gross margin, and CAC is 300 dollars. What is the CAC payback period?
Q5.Two companies have a healthy LTV to CAC ratio, but one has a 6-month payback and the other a 14-month payback. Why does this matter?
Practice Out Loud
Your company's revenue is up 40 percent and the team wants to triple the marketing budget tomorrow. In 90 seconds, explain why you want to check CAC, LTV, and the payback period first, using one quick example of a business that grew itself broke. The AI will play an eager colleague who pushes back: but growth is growth, why slow us down?
Try it in real life
This week, pick one company you follow and find one real world example of unit economics that hold up. Write down what you noticed in two sentences.
Wrap up this lesson
Submitting the Quick Check counts. Or mark it here when you feel ready.