LTV to CAC Ratio: How to Calculate It for Ecommerce
LTV to CAC compares what a customer is worth to what they cost to acquire: divide customer lifetime value by customer acquisition cost. A ratio of 3:1 is the common operating target in DTC — below that, growth burns cash; far above it, you are likely underspending on acquisition. Here is the calculation, step by step, and what to do with the answer.
The formula, both halves. Start with LTV: average order value × purchases per year × years retained × gross margin. A $50 AOV, four orders a year, a three-year relationship, and 60% margin gives $360 of lifetime profit per customer. (The full walkthrough, including where each input comes from, is in our customer lifetime value guide.) Then CAC: total acquisition spend for a period — ad spend, agency fees, affiliate commissions, and the discounts you give on first orders — divided by new customers acquired in that period. $30,000 of spend that produced 500 new customers is a $60 CAC. The ratio: $360 ÷ $60 = 6:1.
Reading the number. Under 1:1 means every new customer loses money over their entire lifetime, not just on the first order — the business is paying for the privilege of serving people. Around 3:1 is the conventional healthy band: enough contribution to fund operations and growth after acquisition. Well above 5:1 usually signals underinvestment in acquisition — retention is quietly subsidizing a growth engine running below capacity, and the fix is spending more, not celebrating. The reason the ratio beats either number alone: Bain’s Fred Reichheld showed a 5% improvement in retention lifts profits by more than 25%, because the LTV side compounds over years while CAC only inflates with auction pressure.
Add the companion metric: CAC payback. Two brands can share a 3:1 ratio and live in different worlds. Divide CAC by the margin a customer generates per month: a $60 CAC against $15 of monthly contribution pays back in four months; against $4, it takes fifteen. Payback period is what decides whether growth strains cash flow, which is why finance teams ask for it alongside the ratio.
Segment it or be misled. A blended 3:1 can hide a 6:1 on returning-customer channels and a 1.2:1 on prospecting. Compute the ratio per acquisition channel and per first-product cohort — customers acquired through a discount-led offer typically carry lower repeat behavior, so their true ratio runs below the blend. The segmented view tells you where the next dollar should actually go.
Three mistakes that corrupt the math. Using revenue LTV instead of margin LTV — a 6:1 revenue ratio at 30% margin is really 1.8:1. Ignoring discount costs inside CAC — a 20% first-order code is acquisition spend, even though it never appears in your ad account. And projecting LTV over horizons your data cannot support — with 18 months of order history, do not model five-year value.
Moving the ratio. CAC is an auction you bid in; LTV is a program you own. The channels that move the numerator — email flows, SMS, loyalty, subscriptions — are exactly what a retention marketing agency operates, and the case for working that side is the whole argument of retention vs acquisition.
Recalculate on a schedule, and agree who owns it. The ratio drifts — CAC moves with auction pressure and creative fatigue, LTV moves with every flow, loyalty, and pricing change — so a number computed once a year is a museum piece. Quarterly is the working cadence: refresh LTV from the latest cohorts, refresh CAC from the trailing quarter’s spend, and log both so the trend is visible. Ownership matters as much as cadence. Marketing tends to quote the flattering revenue-based version; finance wants margin and payback. Put one shared definition in writing — margin-based LTV, all-in CAC, 12-month horizon — and have both teams report against it. Half the LTV:CAC arguments inside DTC brands are two departments using two definitions, both correct, neither comparable.
Run yours now. Two minutes, no spreadsheet: the free customer lifetime value calculator produces the LTV side, your ad account produces the CAC side. Divide, and you know which side of 3:1 you are on — and which lever to pull next.
