Short answer: Unit economics is the profit or loss a business makes on a single customer. Three numbers define it: CAC = total sales and marketing spend in a period divided by new customers acquired in that period; LTV = average monthly gross profit per customer multiplied by expected lifetime in months; and the LTV:CAC ratio, which is considered healthy at 3:1 or above. A stable digital business recovers its CAC in under 12 months.
Why most digital businesses measure the wrong thing
Plenty of companies track revenue, ROAS and lead volume, and conclude from them that the business is healthy. All three can rise while the company loses money on every new customer, because they measure motion rather than profitability. Unit economics asks a narrower and far more useful question: how much money is left once a single customer has completed the entire journey, from first click to churn.
Once that number is known, most business decisions get easier: how much you can spend on advertising, whether to raise prices, whether a new product is worth building, and when you can afford to hire.
The three numbers and their formulas
| Metric | Formula | What to include |
|---|---|---|
| CAC Customer acquisition cost |
(Marketing spend + sales spend) / new customers | Media, tools, agency fees, salaries of marketing and sales staff, a proportional share of marketing operations |
| Gross profit per customer | Average monthly revenue − direct costs | Payment processing, hosting, API usage, support time, per-seat software licences |
| LTV Lifetime value |
Monthly gross profit × lifetime in months | Lifetime = 1 / monthly churn rate. A 5% monthly churn equals 20 months of life |
| LTV:CAC ratio | LTV / CAC | Below 1 you burn cash. 1 to 3 is fragile. 3 and above is healthy. Above 5 usually signals under-investment in growth |
| Payback period | CAC / monthly gross profit | Practical target for a mid-sized business: under 12 months, ideally under 6 |
A full worked example
A digital services business on monthly retainers. Quarterly figures:
| Input | Value | Notes |
|---|---|---|
| Media spend for the quarter | 25,000 USD | Google and Meta |
| Sales and marketing salaries | 17,000 USD | Proportional share of two people |
| New customers signed | 15 | Closed deals, not leads |
| CAC | 2,800 USD | 42,000 / 15 |
| Average monthly retainer | 1,700 USD | |
| Direct cost per customer | 1,020 USD | 60% of revenue, mostly delivery hours |
| Monthly gross profit | 680 USD | 40% margin |
| Monthly churn | 4% | Average customer stays 25 months |
| LTV | 17,000 USD | 680 × 25 |
| LTV:CAC | 6:1 | Healthy, and a hint that budget could increase |
| Payback period | 4.1 months | 2,800 / 680 |
Watch what happens when a single input changes. If churn rises from 4% to 8%, lifetime drops to 12.5 months, LTV shrinks to 8,500 USD and the ratio falls to 3:1. Improving retention is almost always the cheapest lever in the model, ahead of lowering CAC and ahead of raising prices.
Reference ranges by business type
| Business type | Reasonable LTV:CAC | Payback period | Strongest lever |
|---|---|---|---|
| B2B SaaS | 3:1 to 5:1 | 12 to 18 months | Churn reduction and account expansion |
| Retainer services | 4:1 to 6:1 | 3 to 6 months | Gross margin and delivery efficiency |
| E-commerce | 2.5:1 to 4:1 | First to second order | Repeat purchase rate and basket size |
| Courses and info products | 3:1 and above | First transaction | Sales page conversion rate |
| Marketplace | 3:1 and above | 6 to 12 months | Liquidity on both sides |
Treat these as starting points rather than rules. A business funded from its own cash flow needs a far shorter payback period than a funded one, simply because it cannot finance the gap.
Where unit economics meets cash flow
A healthy LTV:CAC ratio does not guarantee money in the bank. The gap between the two is timing: you pay CAC today and collect LTV over two years. The faster the business grows, the wider that gap becomes, which is why businesses that are profitable on paper still run out of cash.
The practical rule: multiply monthly new customers by CAC, and that is the cash the business burns on growth every month. If payback takes longer than three months, you need working capital covering at least the payback period multiplied by the acquisition rate.
Four mistakes that make the model useless
- One average for every customer. There are almost always at least two segments with completely different CAC and LTV. A blended average hides the losing one.
- Ignoring leads that never closed. CAC must divide total acquisition cost by customers actually signed, not by leads generated.
- Last-click attribution. A channel that looks expensive under last-click is often the one creating demand. Compare CAC at the mix level, not channel by channel.
- Measuring over too short a window. If average lifetime is 25 months, three months of data cannot estimate LTV. Use cohorts.
How to start measuring this week
You do not need a BI stack. One spreadsheet with six columns is enough: signup month, source, monthly revenue, direct cost, churn month, and attributed acquisition cost. Three months of that data tells you more than any ROAS dashboard. Once the model stabilises, connect it to your CRM as the source of truth and refresh it quarterly.
Frequently asked questions
What counts as a good CAC?
There is no absolute number. A good CAC is one that produces an LTV:CAC ratio of at least 3:1 and a payback period under 12 months. A CAC of 2,800 USD is excellent for a retainer business and disastrous for an e-commerce store.
Should salaries be included in CAC?
Yes. Salaries of marketing and sales staff, including the proportional share of managers involved, are part of acquisition cost. Leaving them out understates CAC artificially, typically by 30% to 50%.
How do you calculate LTV without two years of history?
Use monthly churn to project lifetime: lifetime equals 1 divided by the churn rate. Six months of data gives a reasonable estimate, and you refresh it each quarter as cohorts mature.
What is the difference between LTV and ARR?
ARR is recurring annual revenue at the company level. LTV is cumulative gross profit at the level of a single customer across the whole relationship. ARR measures size, LTV measures quality.
How often should the model be updated?
Quarterly for a stable business, monthly during periods of rapid change: a price change, entering a new channel, or restructuring your packaging. A price change moves all three metrics at once.