Every growth decision eventually reduces to one question: is a customer worth more than it cost to acquire them? The LTV:CAC ratio answers it directly — lifetime value divided by customer acquisition cost. Get it right and you can spend confidently to grow; get it wrong and you’re buying customers at a loss.
The two numbers
CAC (customer acquisition cost) is what it costs, on average, to win one customer:
CAC = total sales & marketing spend ÷ new customers acquiredLTV (customer lifetime value) is the profit a customer generates over their whole relationship with you:
LTV ≈ avg revenue per customer × gross margin × avg lifetimewhere average lifetime ≈ 1 ÷ churn rate. The single most common mistake is using raw revenue instead of gross margin — that overstates LTV by ignoring the cost of actually serving the customer. Always margin-adjust.
What’s a good ratio?
The famous heuristic is 3:1 — each customer worth about three times their acquisition cost. As a sanity check it’s useful:
- Below ~1:1 — you lose money on every customer. Unsustainable unless you’re deliberately buying market share with a plan to fix economics later.
- Around 3:1 — the commonly-cited healthy zone: profitable acquisition with room to invest.
- Well above ~5:1 — often a sign of under-spending. You could likely grow faster by acquiring more, even at a lower ratio.
But 3:1 is a rule of thumb, not a law. It depends on your margins, how long customers actually stay, and — crucially — how long your cash is tied up before it comes back.
Why payback period matters as much
A great LTV:CAC ratio can still strangle a business if the “lifetime” takes years to play out. CAC payback period — how many months of margin it takes to recover acquisition cost — measures the cash reality. Two companies can both hit 3:1, but the one that recovers CAC in 6 months can reinvest far faster than the one that takes 24. Many software teams target payback within roughly a year.
Calculate yours
Use the free CAC & payback calculator to get acquisition cost, the LTV:CAC ratio, and payback period, and the customer lifetime value calculator to build LTV from ARPU, margin, and churn. The inputs only become trustworthy when they’re grounded in real behavior — retention cohorts for churn, conversion for the funnel feeding CAC — which is exactly what product analytics gives you.
The bottom line
Margin-adjust your LTV, treat 3:1 as a compass rather than a target, and watch payback period alongside the ratio. Healthy unit economics aren’t one magic number — they’re a worthwhile customer, won at a sane cost, paid back fast enough to fund the next one.