Lifetime value, against the 3:1 line.

LTV is the total gross profit you expect from a customer across their entire relationship with you. For subscription businesses the margin-adjusted formula is LTV = (ARPA × gross margin%) ÷ churn rate, where ARPA is average monthly revenue per account. Using gross margin rather than raw revenue is what makes the number honest — it reflects retained profit, not topline.

The widely used SaaS benchmark is 3:1 — three dollars of lifetime value for every dollar of customer acquisition cost. Below 1:1 you lose money on every customer. Between 1:1 and 3:1 growth is thin and expensive. 3:1 to 5:1 is the healthy, fundable zone. Above 5:1 usually signals you're under-investing in growth and leaving market share on the table.

Divide lifetime value by customer acquisition cost: ratio = LTV ÷ CAC. If a customer is worth $1,600 in lifetime gross profit and costs $400 to acquire, the ratio is 4:1. CAC should include all sales and marketing spend divided by new customers won in the period.

Two levers: raise LTV or lower CAC. Lift LTV by reducing churn (the single biggest driver — it sits in the denominator), expanding revenue per account, or improving gross margin. Lower CAC with better targeting, stronger conversion, and product-led or referral growth. Reducing churn from 5% to 3% monthly raises LTV by two-thirds on its own — often the product and onboarding work that makes that happen is exactly where engineering pays for itself.