LTV:CAC Explained: The 3:1 Rule and the Cash Behind It
Two numbers decide whether a growth engine is real: what a customer contributes over their lifetime (LTV) and what it costs to acquire them (CAC). The ratio between them is the quiet law of every subscription and repeat-purchase business.
- Healthy LTV:CAC is around 3:1; below 1:1 you buy revenue at a loss; above 5:1 you are likely underinvesting.
- Compute LTV on gross margin, not revenue — revenue-based LTV flatters every business model.
- Payback period is the cash-flow constraint: a great ratio with an 18-month payback still needs runway.
The ratio and its bands
LTV:CAC compares lifetime gross profit per customer with acquisition cost. At 3:1, each marketing dollar returns three in contribution — enough to fund overhead, product and error. Below 1:1, growth spending loses money by construction.
Above 5:1 is not automatically brilliant: it often means the market will bear much more spend than you are committing. If every dollar returns five, the constraint is your budget, not the market.
Compute LTV on margin, or don't compute it
Revenue-based LTV is the most common inflation. A customer generating $600 of revenue at 40% margin contributes $240 — and the acquisition budget competes with $240, not $600.
The formula chain: LTV = average order × purchases per year × margin % × lifespan. Lifespan comes from churn: at 4% monthly churn, average life is 1 ÷ 0.04 = 25 months. Our customer lifetime value calculator runs the full chain including the ratio and payback.
Payback: the second test
A 3:1 ratio with a 20-month payback needs 20 months of funding per customer before their contribution returns. A 3:1 ratio with 3-month payback is self-funding growth. Same ratio, wildly different cash reality.
Payback (months) = CAC ÷ monthly gross profit per customer. For venture-scale growth, sub-12-month payback is the usual bar; bootstrapped businesses should want sub-6.
The churn lever nobody prices
Teams fight over CAC — harder targeting, better landing pages — while churn sits untouched. Cutting monthly churn from 5% to 3% raises average lifespan from 20 to 33 months, nearly doubling LTV without touching marketing.
Retention improvements compound across the entire existing base, not just new cohorts. It is usually the highest-leverage move on the board, and it never shows up in the ad platform's dashboard.
Try the calculators
Customer Lifetime Value Calculator
Enter how customers buy (order value, frequency, margin, lifespan) and what you pay to acquire them, to see lifetime value, the LTV:CAC ratio and payback period.
ROAS Calculator
Enter ad spend and attributed revenue to see ROAS, actual profit after product costs, and the break-even ROAS your gross margin requires.
Profit Margin Calculator
Enter revenue, cost of goods sold and operating expenses to see gross profit, gross margin, net profit and net margin — the two numbers that describe a business’s health.
Frequently asked questions
What is a good LTV:CAC ratio?
About 3:1. Below 1:1 loses money on every acquisition; persistently above 5:1 usually signals you can spend more on growth.
How do I estimate customer lifespan?
For subscriptions, lifespan ≈ 1 ÷ monthly churn rate. For transactional businesses, use repeat-purchase cohort data or conservative industry benchmarks.