LTV:CAC Ratio — A Field Guide

The LTV:CAC ratio compares what a customer is worth over their lifetime against what it cost to acquire them. It is the classic test of whether growth is profitable, and it is also the most gamed metric in SaaS, because both sides depend on assumptions you can quietly make generous. Calculated honestly it is invaluable; calculated hopefully it is a story you tell yourself.

Calculate CAC fully

Customer acquisition cost is total sales and marketing spend over a period divided by the customers acquired in it. The common error is under-counting the numerator — including ad spend but not the salaries, tools, and overhead of the sales and marketing teams. CAC that ignores the people doing the acquiring is not CAC; it is a fraction of it, and it makes the ratio look far better than reality.

Calculate LTV conservatively

Lifetime value is the profit a customer generates over their relationship with you. A sound approximation: average revenue per customer times gross margin, divided by the churn rate. Two honesty checks: use gross margin, not revenue — you keep only the margin, not the top line — and use a real, current churn rate. A low churn assumption inflates the implied lifetime dramatically, which is exactly why over-optimistic LTVs are so common.

LTV = (ARPA x gross_margin%) / churn_rate
CAC = (all sales + marketing cost) / customers_acquired
ratio = LTV / CAC     # aim ~3:1; also check payback separately

Read the ratio, with payback beside it

A ratio around 3:1 is the common healthy benchmark: much lower and you are barely (or not) recovering acquisition cost; much higher can mean you are under-investing in growth. But the ratio alone hides timing. LTV plays out over years, while CAC is spent now — so pair it with CAC payback period, the months to recover acquisition cost. A great ratio with a two-year payback still strains cash flow, because you fund the acquisition long before the lifetime value arrives.

LTV:CAC is a powerful test of unit economics when both sides are computed honestly — full acquisition cost, margin-based lifetime value, real churn — and read alongside payback period and segmentation. Calculated that way it tells you whether buying growth is a good trade; calculated hopefully it just tells you what you wanted to hear.