Unit Economics: The Formula That Predicts Profitability

Customer Acquisition Cost (CAC) is simple: divide all marketing and sales spend by the number of new customers. If you spend $50k on ads in January and acquire 100 customers, your CAC is $500. Lifetime Value (LTV) is total profit from a customer over their entire relationship: if a customer pays $150/month for 24 months at 70% gross margin, LTV is $150 × 24 × 0.70 = $2,520. The LTV:CAC ratio tells you if your model works: ratios above 3:1 mean every dollar spent on acquisition returns $3 in profit.

Most early-stage founders get CAC wrong by including all marketing spend. Use fully-loaded cost: if a marketing manager costs $100k/year and they onboard 200 customers annually, add $500 to each customer's CAC. Similarly, LTV must reflect churn. A $100/month customer with 80% annual retention survives 5 months on average (1 ÷ 0.20), so LTV = $100 × 5 × 0.70 = $350. If your CAC is $500 and LTV is $350, you lose money on every customer—no amount of growth fixes this.

CAC payback period answers: how many months until a customer pays back what you spent acquiring them? Divide CAC by monthly contribution margin (revenue minus cost of goods sold, not including operating expenses). If CAC is $500 and contribution margin is $100/month, payback is 5 months. SaaS companies rarely scale aggressively until payback drops below 12 months; anyone paying more than 18 months is likely hemorrhaging cash.

Payback period tells you how much working capital you need. If payback is 15 months and you're acquiring 100 customers monthly, you must fund 1,500 customers' acquisition costs before revenue catches up. That's $750k in cash committed (100 customers × 15 months × $500 CAC). If your runway is 12 months and you're growing aggressively, payback longer than 10 months means you'll run out of cash before profitability.

Gross margin = (revenue – cost of goods sold) ÷ revenue. A SaaS company with $1M ARR and $200k in hosting, payment processing, and support has 80% gross margin—$800k goes to operating expenses. A marketplace with $1M GMV and 30% take-rate plus $150k in payment fees has only $150k gross profit (15% margin). Same revenue, but the marketplace burns 5× the cash because product costs eat the money.

Benchmark against your category: B2B SaaS typically targets 75%+ gross margin; B2C SaaS 70%; marketplaces 30–40%. If you're below category benchmark, your unit economics won't work at scale. YouTube took 15 years to become profitable not because of competition, but because video delivery and moderation at scale destroyed margins. Know your gross margin before spending money on growth.

Before spending $100k on an acquisition campaign, run a microtest: spend $5k–$10k on a single channel and measure actual CAC, not estimated CAC. If you spend $7k on LinkedIn ads and acquire 10 customers, CAC is $700. Calculate LTV from those 10 customers (wait 3 months, see how many still pay). Use that real LTV:CAC ratio to forecast: if it's 2:1 at small scale, assume it's 2:1 at large scale (often worse due to channel saturation). Never scale a channel until you have 30+ customer transactions and 60+ days of retention data.

Test different pricing tiers. If 80% of customers choose your $99/month plan but they churn in 4 months, and 20% choose $499/month with 18-month retention, LTV differs wildly. A customer paying $99 × 4 × 0.70 = $277 versus $499 × 18 × 0.70 = $6,283. If acquisition cost is the same, the expensive tier funds growth; the cheap tier does not. Small changes to conversion funnels and price perception shift unit economics from 'can't scale' to 'must scale.'