Unit Economics 101: The Numbers Every Founder Must Understand

Most founders understand revenue. Fewer understand whether their revenue is actually sustainable.

Unit economics answers that question at the level of a single customer: does the revenue from this customer justify the cost of acquiring and serving them?

The Core Metrics

Customer Acquisition Cost (CAC) How much do you spend, on average, to acquire one customer?

CAC = Total sales & marketing spend in a period ÷ New customers acquired in that period

If you spent $10,000 on ads and sales this month and acquired 20 customers, your CAC is $500.

Customer Lifetime Value (LTV or CLV) How much revenue do you expect from a customer over the entire relationship?

For a subscription product: LTV = Average revenue per user (ARPU) ÷ Churn rate

If your product costs $100/month and 5% of customers churn each month: LTV = $100 ÷ 0.05 = $2,000

The LTV:CAC Ratio The primary measure of whether your business is viable.

Using the above examples: LTV:CAC = $2,000 ÷ $500 = 4:1

Benchmarks:

• Under 1:1: You're losing money on every customer (unsustainable)
• 1:1-3:1: Marginal, needs improvement
• 3:1: The general target for early-stage SaaS
• 5:1+: Strong, can invest heavily in growth

Payback Period How many months does it take to recover your CAC?

Payback Period = CAC ÷ (ARPU × Gross Margin %)

If CAC = $500, ARPU = $100, gross margin = 80%: Payback = $500 ÷ ($100 × 0.8) = 6.25 months

Target: under 12 months for most SaaS, under 18-24 for enterprise.

The Churn Problem

Every metric above is dramatically affected by churn. A product with 10% monthly churn has a fundamentally different unit economics story than one with 2% monthly churn, even if the revenue and CAC look identical.

10% monthly churn = average customer lifetime of 10 months 2% monthly churn = average customer lifetime of 50 months

The second product can afford much higher CAC and still be profitable.

Fix churn before scaling acquisition. Always.

What to Do With This

If your LTV:CAC is below 3:1, one or more of these is true:

• Your price is too low
• Your churn is too high
• Your acquisition costs are too high
• Your gross margins are too low

Each has a different fix. Identify which is the root cause before optimizing.

The good news: at early stage, you don't need perfect numbers. You need directionally correct numbers and a plan to improve them. Investors at pre-seed and seed understand this.

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