The two numbers, defined
CAC (Customer Acquisition Cost) = Total spend to acquire customers ÷ Number of new customers acquired in that period. If a $2,000 ad spend brought in 100 new customers, CAC = $20.
LTV (Lifetime Value) = The total gross margin a customer generates over the time they keep buying from you — not just their first order. A simplified version: LTV = Average order value × Gross margin % × Average number of orders per customer over their relationship with you.
Why the ratio matters more than either number alone
CAC of $20 sounds fine or terrible depending entirely on what that customer is worth over time. LTV:CAC ratio is the number that actually tells you whether acquisition spend is working:
- LTV:CAC below 1:1 — you're losing money acquiring every customer, even before overhead. Not sustainable regardless of how much revenue it generates.
- LTV:CAC around 1:1 to 2:1 — thin; you're likely only marginally profitable on acquisition once true costs (not just ad spend, but fulfillment, support, and returns) are included.
- LTV:CAC of 3:1 or higher is a commonly cited healthy target in DTC ecommerce, though the "right" number depends heavily on your category, margin structure, and how quickly you need to recover cash (see payback period below) — treat any single benchmark as a starting point to sanity-check against, not a hard rule.
Worked example
You spend $3,000 on ads in a month and acquire 150 new customers. CAC = $3,000 ÷ 150 = $20.
Of those customers, historical data shows an average of 2.4 orders over their first year at an average order value of $35, with a 40% gross margin.
LTV = $35 × 0.40 × 2.4 = $33.60.
LTV:CAC = $33.60 ÷ $20 = 1.68:1 — positive, but below the commonly cited 3:1 healthy target. This customer base is not yet clearly unprofitable to acquire, but the margin of safety is thin — a modest CAC increase or a drop in repeat rate could flip it negative.
Payback period: the other half of the picture
LTV:CAC tells you if acquisition is eventually worth it; payback period tells you how long it takes to recover the acquisition cost — critical for cash flow, since you pay CAC upfront but LTV arrives over months or years.
Worked example (same numbers): If the $33.60 LTV arrives across 2.4 orders spread over roughly 8 months on average, and the first order alone contributes $35 × 0.40 = $14 of gross margin, you haven't recovered the full $20 CAC until partway into the second order — a payback period of roughly 4-5 months in this simplified example. A business with limited working capital needs to survive that gap for every new customer cohort, not just be profitable on paper eventually.
Why marketplace sellers have a harder time with this than DTC sellers
On most marketplaces, you don't own the customer relationship the way you do on your own site — limited access to customer contact info, no owned email/SMS channel in most cases, and the marketplace (not you) often decides whether a repeat purchase happens through your listing again. This makes LTV harder to measure directly and, in many marketplace-only businesses, genuinely lower than an equivalent DTC relationship — factor this in rather than importing a DTC-world LTV:CAC benchmark uncritically into a marketplace-only business.
Improving the ratio
- Lower CAC: tighten ad targeting, improve conversion rate (better listing content/images), reduce reliance on the most expensive acquisition channels.
- Raise LTV: improve repeat purchase rate (post-purchase follow-up where the platform allows it, product quality that earns organic repeat visits), increase average order value (bundles, cross-sell), or expand margin per order.
- Shorten payback period: this matters independently of the ratio — a business tight on cash should weight payback speed heavily even when the eventual LTV:CAC looks acceptable.
Mistakes
- Calculating LTV using only the first order's margin, understating true customer value if there's meaningful repeat purchase behavior.
- Comparing your LTV:CAC against a DTC-world benchmark when you're a marketplace-only seller with limited repeat-purchase visibility and control.
- Ignoring payback period and judging acquisition spend only on the eventual ratio, even when it strains cash flow to get there.
Checklist
- CAC calculated from total acquisition spend divided by actual new customers, not total orders.
- LTV estimated using real repeat-purchase and average-order-value data where available, not a first-order-only estimate.
- LTV:CAC ratio calculated and compared against your own margin-informed target, not a generic benchmark.
- Payback period estimated and checked against your actual cash runway.