Analyze SaaS unit economics

Direct answer

Compare the cost of acquiring a customer (CAC) with the gross profit that customer generates. Report CAC payback in months and estimate lifetime value (LTV) using observed retention, not revenue alone. If sales and marketing spend, customer counts, or subscription history are missing, do not present a calculated ratio as fact.

Why this question comes up

Growth can increase revenue while acquisition costs remain unrecovered. CAC payback shows the time needed to earn back those costs; LTV depends on how long customers stay and what they spend.

Records to gather

• Revenue by customer and cohort, by month
• Gross margin, with direct hosting, support, and customer-success costs allocated under a stated policy
• Sales and marketing spend by period, including salaries and commission
• New customer counts by month, tied to the spend that produced them
• Churn and expansion by cohort, in both customer count and revenue

Review workflow

1. Define CAC. Divide the sales and marketing costs of acquiring a cohort by its new customers. State whether salaries, commissions, tooling, and advertising are included; paid-media cost alone is a different measure.
2. Estimate LTV from gross profit. Apply a stated gross-margin policy and observed retention to customer revenue. The shortcut monthly revenue per customer × gross margin ÷ monthly customer churn assumes a stable churn rate; test it against cohort history when available.
3. Compare cohorts. Show acquisition cost, retention, and expansion for customers acquired in the same period. A blended average can hide a weaker recent cohort.
4. Show gross and net revenue retention. Gross excludes expansion; net includes it. Expansion can offset losses without improving customer retention.
5. Calculate payback in months. Divide CAC by monthly gross profit per acquired customer. If revenue or margin changes over time, use cumulative monthly gross profit instead of a fixed-month shortcut.
6. Account for the sales cycle. If spend precedes signup, match it to the cohort it helped acquire and disclose the lag assumption.

What a useful answer should include

• CAC with its definition stated, and the components included
• LTV calculated on gross margin, with the retention assumption made explicit
• Cohort retention curves rather than a blended average
• Gross and net revenue retention reported separately
• CAC payback in months alongside any LTV:CAC ratio
• The lag assumption between spend and customer acquisition

Common failure modes

• Revenue-based LTV. Ignoring delivery costs overstates the amount available to recover acquisition spend.
• Blended retention. An average can hide a weaker recent cohort.
• Net retention alone. Expansion from existing accounts can offset losses while customer count falls.
• Same-period CAC without a lag check. This month’s spend may not have produced this month’s customers.
• Treating a benchmark as a target. Published SaaS benchmarks come from different stages, models, and segments. They are context, not a goal.