LTV vs CAC: Which to Use When Funding Growth
By Devon Coombs, CPA, MBA · Teaching Professor of Finance, Santa Clara University · Reviewed August 2026
Use LTV to judge what a customer is worth and CAC to judge what acquiring one costs; the growth decision comes from comparing the two on a margin basis. A ratio around 3:1, with LTV computed on gross margin rather than revenue, generally supports continued acquisition spend. The CAC payback period then decides whether the company can afford that spend, because it measures how long acquisition dollars stay tied up before contribution recovers them.
| Customer Lifetime Value (LTV) | Customer Acquisition Cost (CAC) | |
|---|---|---|
| What it measures | Margin a customer generates over the full relationship | Fully loaded sales and marketing cost per new customer |
| How it is computed | Revenue per customer x gross margin x lifespan (or divided by churn) | Total sales and marketing spend divided by new customers in the period |
| Nature of the number | Forecast resting on churn and margin assumptions | Mostly observed, current-period cost |
| Cash timing | Collected gradually over the customer's life | Paid up front, before revenue arrives |
| Typical distortion | Overstated by using revenue instead of gross margin | Understated by omitting salaries, tools, and overhead |
| Decision it drives | Whether a customer is worth acquiring | What acquisition consumes in cash today |
When Customer Lifetime Value (LTV) is the right tool
LTV is the right measure when the question is whether a customer relationship creates value at all, and when ranking segments, channels, or cohorts against each other. Compute it on gross margin, not revenue, and treat the churn assumption with suspicion at a young company, since a few quarters of retention data rarely support a multi-year lifespan estimate. LTV is a forecast, so it serves best for direction and comparison rather than as a bankable number.
When Customer Acquisition Cost (CAC) is the right tool
CAC is the operative number for budgeting and cash planning because it is largely observed rather than forecast. Fully load it with salaries, commissions, tools, and program spend, not just media, and track blended CAC alongside paid CAC so organic acquisition does not flatter the paid channels. When CAC rises across successive cohorts, that trend usually says more about the next dollar of growth spend than any lifetime value estimate does.
The common mistake
The common error is reading a healthy LTV:CAC ratio as a license to spend. The ratio compares a forecast that arrives over years against a cost paid today, so a 4:1 business with a 24 month payback period can run out of cash while its unit economics look excellent on paper. Operators tend to inflate LTV by using revenue instead of gross margin and by extending lifespan assumptions beyond what cohort data supports. The discipline is to fund growth against the payback period and margin-adjusted LTV, not against the headline ratio.
Work the numbers yourself
Both concepts are taught in depth, with practice questions, in the free Entrepreneurial Finance course.