LTV:CAC Ratio — What It Is and What a Good Number Looks Like

Published 2026-06-30 · By the CalculatorHive editorial team

LTV:CAC is the ratio every investor deck opens with and the one most founders calculate wrong. The formulas are simple arithmetic; the errors are all in the inputs. This walks through how to compute both halves properly, what the 3:1 rule of thumb actually means, why CAC payback period matters more than the ratio in the short run, and the specific mistakes — using revenue instead of gross profit, blending organic customers into paid CAC — that inflate the number by 25% or more.

How do you calculate LTV?

Customer lifetime value is the total gross profit you expect from an average customer before they leave. For a subscription business the standard form is:

LTV = (ARPA × gross margin %) ÷ churn rate

ARPA is average revenue per account per month. Gross margin is revenue minus the direct cost of serving that customer — hosting, third-party APIs, payment processing, support salaries — expressed as a percentage. Churn rate is the share of customers you lose each month.

Dividing by churn works because 1 ÷ churn is the average customer lifetime in months. A 2% monthly churn rate implies an average life of 50 months; 5% implies 20 months. So the formula is really "monthly gross profit × how many months you keep them."

Take a business charging $80 per month, running an 80% gross margin, losing 2% of customers per month:

• Monthly gross profit per customer: $80 × 0.80 = $64
• Average lifetime: 1 ÷ 0.02 = 50 months
• LTV: $64 × 50 = $3,200

The LTV calculator runs this for your own figures, and the churn rate calculator converts customer counts into the monthly rate the formula needs.

How do you calculate CAC?

Customer acquisition cost is total sales and marketing spend divided by the number of new customers that spend produced:

CAC = (sales spend + marketing spend) ÷ new customers acquired

"Spend" means fully loaded: ad budget, agency and contractor fees, marketing software, content production, plus the salaries and commissions of everyone in sales and marketing. Leaving out headcount is the most common way founders quietly halve their own CAC.

Suppose that same business spent $60,000 across a quarter and signed 120 new customers. CAC is $60,000 ÷ 120 = $500. Those 120 customers at $80 each also added $9,600 of new monthly recurring revenue — the MRR and ARR calculator is where that side of the ledger lives.

Put the two together: $3,200 ÷ $500 = a 6.4:1 LTV:CAC ratio. Use the CAC calculator to work out the denominator for your own period.

Why is 3:1 the benchmark?

The 3:1 figure is not a law of nature — it is a rough allocation of the gross profit a customer generates. One unit of that profit repays the cost of acquiring them. A second covers the overhead they don't directly consume: engineering, product, finance, legal, office. The third is what's actually left as profit or reinvestment. A business at 1:1 is running a very expensive customer-acquisition treadmill; below 1:1 it is paying for the privilege of having customers, and more growth makes the hole deeper.

Less obvious is that a very high ratio is also a signal, not a trophy. A company at 8:1 or 10:1 is usually leaving growth on the table: there is almost certainly a next tier of channels or segments with worse unit economics that still clears 3:1. The ratio is a guardrail for how hard to push, not a score to maximise. In our example, 6.4:1 says there is room to spend more aggressively before economics become the constraint.

One caveat that matters for early-stage companies: if you have been selling for eight months, you do not have enough retention history to know your churn rate, and therefore you do not know your LTV. The ratio is close to meaningless before you have observed a meaningful chunk of a real customer lifetime.

What is CAC payback period, and why does it matter more?

LTV:CAC tells you whether a customer is profitable eventually. It says nothing about when. Payback period fills that gap:

CAC payback (months) = CAC ÷ (ARPA × gross margin %)

In the example: $500 ÷ $64 = 7.8 months. That is how long the customer has to stay before you have recovered what you spent to acquire them. Under 12 months is generally considered healthy for B2B software; under 6 months is strong; beyond 18 months you have a cash-flow business problem even if the lifetime ratio looks fine, because every new customer is a loan you are making to yourself.

This is why two companies with identical 3:1 ratios can be in completely different situations. One recovers CAC in five months and can reinvest the cash into more acquisition three times a year. The other recovers it in 22 months and needs external funding just to keep the growth rate flat.

How much does churn actually change LTV?

More than anything else on the list. Because lifetime is 1 ÷ churn, the relationship is hyperbolic: improvements at low churn rates are worth far more than the same percentage-point improvement at high rates. Holding ARPA at $80 and gross margin at 80% — so $64 of gross profit per month — and CAC at $500:

Going from 5% to 2% monthly churn multiplies LTV by 2.5× and moves the business from a marginal 2.6:1 to a comfortable 6.4:1 — without touching price, spend, or conversion rate. Going from 2% to 1% doubles it again. That asymmetry is why retention work usually outranks acquisition work once you are past the earliest stage.

Note the bottom rows. At 10% monthly churn the average customer is gone in ten months and CAC payback is 7.8 months, so you make about two months of profit before they leave. High-churn businesses are not fixed by better ads.

The mistakes that inflate the ratio

Using revenue instead of gross profit. The single most common error. Skip the margin term and LTV becomes $80 × 50 = $4,000, and the ratio becomes 8:1 instead of 6.4:1. The overstatement is exactly 1 ÷ gross margin — 25% at an 80% margin, 43% at a 70% margin, and worse for anything with hardware, shipping, or heavy human delivery. If your "SaaS" involves an implementation team, your true margin may be closer to 60% and the distortion approaches 67%.

Blending organic customers into paid CAC. If 40 of those 120 customers arrived through word of mouth and would have arrived with no spend at all, then $60,000 bought 80 customers, not 120. Paid CAC is $750, and the ratio falls from 6.4:1 to 4.3:1. Blended CAC (all spend ÷ all customers) is the right number for judging overall company efficiency; paid CAC is the right number for deciding whether to increase a specific budget. Reporting the blended figure while making channel decisions is how marketing budgets get scaled into unprofitability.

Ignoring the lag between spend and signup. Dividing this month's spend by this month's customers assumes instant conversion. With a 60-day sales cycle, a month of rising spend makes CAC look artificially high and a month of falling spend makes it look artificially good. Match spend to the cohort it actually produced.

Forgetting expansion revenue. If accounts upgrade over time, ARPA is not static and the simple formula understates LTV. Businesses with negative net revenue churn — expansion exceeding lost revenue — genuinely break the model, and need a cohort-based calculation instead of a single divide.

Common questions

Should I use monthly or annual churn in the LTV formula?

Match the units. If ARPA is monthly, use monthly churn and you get lifetime in months. If you only have an annual figure, don't just divide by 12 — churn compounds. An annual retention rate of 80% implies a monthly churn of about 1.8%, not 1.67%, because the survivors each month are a shrinking base. For annual contracts, run the whole calculation annually instead.

Does LTV:CAC work for e-commerce or a service business?

Yes, but the lifetime term changes. Without subscriptions there is no churn rate, so LTV is built from average order value × purchase frequency per year × expected years of custom × gross margin. The 3:1 guidance still applies, though e-commerce typically runs on thinner margins and shorter repeat horizons, so many operators judge a first-order contribution margin instead and treat repeat purchases as upside.

Where do customer success salaries belong — CAC or gross margin?

Split by function, not job title. Work that wins new revenue (onboarding demos, sales-assist) belongs in CAC. Work that keeps existing customers alive (support, ongoing account management) is a cost of service and belongs in gross margin, where it reduces LTV. Putting all of customer success into CAC flatters LTV and inflates the ratio; putting all of it into margin flatters CAC. Pick a split, document it, and keep it consistent across periods.

What LTV:CAC ratio do investors expect to see?

3:1 is the figure most commonly quoted as a floor for a healthy subscription business, usually paired with a CAC payback under 12 months. But experienced investors care more about the trend and the honesty of the inputs than the headline. A defensible 2.5:1 that is improving quarter over quarter, with churn measured over a real observation window, reads far better than a 9:1 built on revenue instead of gross profit and three months of retention data.