The LTV/CAC ratio answers one question a founder and an investor both care about: does bringing in a customer pay off, and by how much? It puts the lifetime value of a customer (LTV) over what it cost to acquire them (CAC), and the number that comes out tells you whether you have a growth engine or a money furnace dressed up as one.
Most articles hand you the formula and a magic number and send you on your way. The problem is that the formula is the easy part. The ratio lies more often than it tells the truth, because three ordinary mistakes inflate it until a business that's burning margin looks like it's printing money. This page gives you the formula, a worked example, the benchmark to read it against, a calculator, and — the part that matters — how to keep the number honest.
What LTV/CAC actually measures
Read it as the efficiency of your growth, not a trophy. A high ratio doesn't mean "grow faster" and a low one doesn't mean "you're doomed". It means: for every euro you spend to win a customer, how many euros of margin does that customer return over their whole life with you?
That framing matters because LTV/CAC is easy to weaponise as a vanity metric. Calculate LTV on revenue instead of margin, blend your cheap organic customers into your paid ones, invent a customer lifetime out of optimism, and you can conjure a beautiful ratio that falls apart the moment you pour real money into acquisition. The ratio is only as good as the three inputs underneath it.
The formula, with a worked example
The formula is short:
- LTV = annual contract value × gross margin × average customer lifetime (in years)
- CAC = everything spent to acquire a customer (tools, ads, and the human hours) ÷ customers acquired
- LTV / CAC = the ratio
Let me narrate it with a real case from the book — Flowdesk, an invoice-reconciliation SaaS.
Flowdesk closes new customers through outbound. Adding up the tools and the setup-and-operation time, its CAC lands around €6,000 per customer. Its contract value is €12,000 a year, and customers stay roughly three years (an annual churn near 33%). So the naive LTV is 12,000 × 3 = €36,000, and the ratio is 36,000 / 6,000 = 6:1.
Six euros of value for every euro spent acquiring. Comfortably above the healthy floor of ≥ 3:1. On paper, this channel begs for more fuel.
But watch what happens when you calculate LTV the honest way — on gross margin, not revenue. With an 80% margin, Flowdesk's real LTV is 12,000 × 0.8 × 3 = €28,800, which gives an LTV/CAC of 4.8:1. Still healthy, still worth accelerating — but a full ratio point lower than the vanity version. That gap is the whole game. On a business with thinner margins, that same correction is what turns a "3.5:1, let's scale" into a "2.2:1, fix this first".
The benchmark — a place to look, not the answer
The healthy band for LTV/CAC is ≥ 3:1. Below it, the rule is blunt: don't scale, fix the efficiency first. Pour acquisition spend into a sub-band ratio and you just lose money faster.
Here's the nuance almost every guide skips: the benchmark is a diagnostic, not a verdict. A ratio inside the healthy band tells you where to look, not that you've won. Land far above it — say, 8:1 or 10:1 — and the honest reading isn't "we're brilliant". It's usually "we're underinvesting": you could be spending more to grow faster and you're leaving the market to a competitor. A ratio that's too high is a signal, same as one that's too low. The band is the range where the question changes from "is this broken?" to "how hard do I push?".
Calculate your LTV/CAC ratio
Drop in your four numbers and the calculator returns your ratio, reads it against the healthy band, and — critically — computes LTV on gross margin so you get the honest number, not the inflated one.
Run your numbers
The three mistakes that inflate your ratio
Almost every too-good-to-be-true ratio comes from one of these three.
1. Calculating LTV on revenue instead of gross margin
This is the silent one. Revenue is what the customer pays you; margin is what you keep after the cost of serving them. LTV built on revenue counts euros you never actually pocket. As we saw with Flowdesk, moving from revenue to an 80% margin dropped the ratio from 6:1 to 4.8:1 — and on a services-heavy business with a 50% margin, it would halve. The numbers "add up" and you overpay for every customer anyway. Always calculate LTV on margin.
2. Blended CAC instead of paid, channel by channel
The book's core discipline is that CAC judges a channel, not a company average. "Blended" CAC mixes your nearly-free customers — word of mouth, organic search, referrals — in with the ones you paid hard for. The average looks great precisely because the free customers are subsidising the expensive ones. The moment you try to scale by spending more, you're scaling the paid channel in isolation, and its true CAC is far higher than the blend suggested. Look at the paid number, per channel, before you decide anything.
3. Inventing a lifetime instead of measuring cohort churn
LTV hinges on how long customers stay, and "how long" is not a guess — it's roughly 1 ÷ annual churn, measured on cohorts. Take everyone who came in one month and track what share is still paying month after month. If you assume five years of tenure when your cohorts flatten at eighteen months, your LTV — and your ratio — is fiction. Early on, before you have long cohorts, be conservative; an optimistic lifetime is the easiest way to lie to yourself.
When a healthy ratio still says "don't scale"
Even a clean, honest, above-band ratio isn't a green light on its own — because LTV/CAC says nothing about timing. That's what payback covers: how many months of subscription it takes to earn the CAC back. Flowdesk recovers its €6,000 CAC in about six months of subscription (€1,000/month), and a healthy payback sits < 12 months.
The nuance that separates a specialist from a spreadsheet: payback has to fit inside the client's runway. A pre-seed startup with eight months of cash cannot afford a channel with a twelve-month payback, even if its LTV/CAC is textbook-healthy — it runs out of money before it earns the customer back. The less runway, the shorter the payback you demand, or a channel that charges up front. That's why you ask about the cash before you recommend hitting the accelerator. A ratio judges whether a channel is profitable; payback-against-runway judges whether you can survive long enough to enjoy it.
Where LTV/CAC fits in the bigger picture
LTV/CAC and payback judge a deal or a channel. When you zoom out to the whole company — especially before raising a round — the questions change to engine-level ratios like the SaaS magic number and the compounding you capture through net revenue retention. If you want to see how a customer's velocity through the funnel feeds all of this, sales velocity is the companion number. And to place unit economics inside a full plan — from ICP to engine to expansion — start with the complete go-to-market strategy guide.
Frequently asked questions
What is a good LTV/CAC ratio?
The healthy band is ≥ 3:1. Read it as a range, not a target to maximise: below it, fix efficiency before scaling; far above it, you're usually underinvesting and could grow faster. The band tells you where to look, not that the job is done.
Should LTV be calculated on revenue or gross margin?
Gross margin, always. Revenue counts euros you don't keep after the cost of serving the customer. In the Flowdesk example, switching from revenue to an 80% margin moved the ratio from 6:1 to 4.8:1 — and on thinner margins the correction bites much harder.
What's the difference between LTV/CAC and CAC payback?
LTV/CAC tells you whether a channel is profitable over the customer's life; payback tells you how fast you get your acquisition cost back. A channel can be profitable long-term (high LTV/CAC) and still be unaffordable short-term if the payback is longer than your runway. You need both.
Why is my LTV/CAC ratio so high?
A ratio well above the healthy band usually means one of two things: you're calculating LTV on revenue or a blended CAC (inflating it artificially), or the number is real and you're underinvesting in growth. Check the inputs first; if they're honest, the too-high ratio is an invitation to spend more.
If these numbers look wrong for your startup — a ratio that's suspiciously high, a payback you can't reconcile with your cash, a CAC you're not sure how to split by channel — that diagnosis is exactly what our GTM audit does: we take your real unit economics apart and tell you where the money is actually going.
Written by Mario Hernández, GTM consultant and founder of creactia, and author of «Go-To-Market: from zero to specialist». I run this exact calculation inside real B2B engagements — the version above is the one I use before recommending a client spend a single euro more on acquisition, because the honest ratio and the vanity ratio are rarely the same number.