Should we include expansion revenue in LTV?

Yes for pure LTV calculation (expansion is real value from the customer), but be explicit — some investors prefer new-logo LTV separated from expansion LTV. Report both.

How does LTV / CAC relate to CAC payback?

CAC payback is the leading indicator; LTV / CAC is the lagging outcome. Payback under 18 months typically produces LTV / CAC above 3x. Both together give a complete efficiency picture.

What if churn is too new to estimate lifetime?

Use conservative caps (4-5 year lifetime max) and cohort-based churn from your longest-tenured cohort. Disclose the calculation methodology. Investors respect honest under-estimation more than aggressive assumptions.

LTV / CAC Ratio: Formula, Benchmarks, and Common Traps

LTV / CAC tells you whether each dollar of customer acquisition generates enough lifetime value to justify the spend. Here's how to calculate it honestly.

LTV / CAC: The Ratio That Justifies Growth Investment

LTV / CAC is the second-most-cited SaaS metric after growth rate. Above 3, investors will fund more S&M spend. Below 1, the business is destroying value. But the calculation is genuinely tricky — and easy to game unintentionally. Here's how to get it right.

The formula

LTV = ARPA × gross margin × average customer lifetime (in months). CAC = fully-loaded S&M cost per new customer. Ratio: LTV / CAC. Example: $12K annual ARPA × 80% gross margin × 4-year lifetime = $38.4K LTV. $12K CAC → LTV / CAC = 3.2x.

Benchmarks

Under 1: business destroys value with each new customer — pause growth spend. 1-3: sub-scale, improve efficiency before scaling. 3-5: healthy, invest more. Above 5: highly efficient but may signal under-investment (worth diagnosing). Growth-stage investors expect 3+ minimum for Series B, 4+ for Series C.

The lifetime estimation problem

Customer lifetime = 1 / (annual churn rate). Example: 10% annual churn → 10-year lifetime. Problem: at early stage, you don't have 10 years of data to validate. Solution: use conservative lifetime estimates (cap at 4-5 years even if churn implies longer) and cite the assumption explicitly. Investors will discount aggressive lifetime assumptions.

Common mistakes

Using revenue instead of gross margin in LTV (inflates by 20-30%). Including expansion revenue in ARPA without adjusting for expansion CAC. Estimating lifetime based on a few outlier long-tenured customers. Excluding fully-loaded S&M from CAC (only counting variable spend, not sales team overhead). Each mistake compounds — a "5x" LTV/CAC calculated incorrectly might be 2x actual.

Frequently asked questions

Should we include expansion revenue in LTV?: Yes for pure LTV calculation (expansion is real value from the customer), but be explicit — some investors prefer new-logo LTV separated from expansion LTV. Report both.
How does LTV / CAC relate to CAC payback?: CAC payback is the leading indicator; LTV / CAC is the lagging outcome. Payback under 18 months typically produces LTV / CAC above 3x. Both together give a complete efficiency picture.
What if churn is too new to estimate lifetime?: Use conservative caps (4-5 year lifetime max) and cohort-based churn from your longest-tenured cohort. Disclose the calculation methodology. Investors respect honest under-estimation more than aggressive assumptions.