See your LTV:CAC ratio — how the lifetime value of a customer compares to what it costs to acquire one. The single clearest read on whether growth is healthy.
Use gross-profit-based LTV (not revenue) for a true read. A very high ratio can also mean you're under-investing in growth. Estimate only.
LTV:CAC compares what a customer is worth over their lifetime to what you paid to acquire them. A ratio around 3:1 is the widely-cited healthy target — below that, growth is expensive; far above it, you may be leaving growth on the table by under-spending.
LTV:CAC = customer lifetime value ÷ customer acquisition cost
LTV:CAC sets what a customer is worth over their whole relationship with you against what you spent to win them. It is the clearest single read on whether growth is creating value or consuming it, which is why it is usually the first ratio an investor asks for. It is also the ratio most easily flattered, because both of its inputs are estimates you construct rather than figures you look up.
LTV:CAC = customer lifetime value ÷ customer acquisition cost
CAC is the more honest of the two if you build it properly: total sales and marketing spend for a period divided by the customers that period produced, including salaries, tools and agency fees — not just ad spend. LTV is where the trouble is, and the single rule that matters is that it must be built from gross profit per customer, not revenue per customer.
The calculator opens with $900 of lifetime value and $300 of acquisition cost. Divide: 900 ÷ 300 = 3, shown as 3 : 1, and the verdict reads Healthy — 3:1 or better. In money rather than ratio: each customer leaves $600 after acquisition, and that $600 is what has to cover support, hosting, overhead, product development and profit.
Now break the assumption. Suppose that $900 was revenue rather than gross profit, and the business runs a 70% gross margin. True lifetime value is 900 × 0.70 = $630, and the ratio falls to 630 ÷ 300 = 2.1 : 1 — below the target, on exactly the same business. Nothing changed except the definition of the numerator. That one substitution is the most common way a healthy-looking unit economic is actually a thin one.
The ratio also says nothing about timing, and timing is what kills companies. Pair it with payback. If that customer's $900 arrives over a twenty-month lifespan, monthly gross profit is 900 ÷ 20 = $45, so the $300 of CAC takes 300 ÷ 45 ≈ 6.7 months to come back. A 3:1 ratio with a six-month payback and a 3:1 ratio with a thirty-month payback are the same ratio and completely different cash positions.
The 3:1 target is a widely-repeated rule of thumb rather than a law, and it is worth knowing why the number sits there: it leaves roughly two-thirds of lifetime value to absorb the costs LTV does not capture and the forecasting error in LTV itself. Below 1:1 you are paying more to acquire a customer than they will ever be worth, which no volume fixes. Between 1 and 3 the model works only if payback is fast or the cost base is thin. Above 5:1 the usual reading is under-investment — there is probably profitable demand you are not buying — though it can also simply mean the LTV estimate is optimistic.
Be sceptical of long LTV horizons in particular. A lifetime value computed over five years for a business eighteen months old is an extrapolation, not a measurement. Capping LTV at a horizon you have actually observed, or at twenty-four months, produces a duller number and a far more defensible one.
The first is the revenue-versus-gross-profit substitution shown above. The second is understating CAC by counting only media spend and leaving out the salaries of the people who do the selling. The third is blending organic and paid customers into one CAC: if half your signups arrive free through word of mouth they drag the average down and hide what the paid channel actually costs at the margin, which is the number that governs whether to spend more. The fourth is ignoring payback, as above. The fifth is treating a ratio computed across the whole business as though it applied to each segment — the small plan and the enterprise plan usually have completely different ratios, and the blended figure describes neither.
A ratio is one number; the decision is per channel, per segment, per month. The working version is a table of acquisition spend and customers won by channel, gross margin applied to revenue per customer, retention by cohort feeding the LTV, and a payback column beside the ratio. Build that and the question stops being “is 3:1 good” and becomes “which channel still returns its cost inside the payback window we can fund.” Our Small Business Bookkeeping template holds the revenue and cost ledger those figures are drawn from.
It leaves room for the costs LTV doesn't capture while still growing profitably. 1:1 means you make nothing; much above 3:1 may mean you could grow faster by spending more.
Gross profit. Revenue-based LTV overstates the ratio because it ignores the cost of serving the customer.
Related: customer lifetime value calculator · customer acquisition cost calculator · churn rate calculator · all free calculators.
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It uses standard formulas and recalculates the moment you change a value, so the math is exact for the inputs you enter. Treat the result as a reliable planning estimate; for decisions with legal or tax consequences, confirm the figures with a qualified professional.
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Last reviewed: September 2026. Free to use, no signup — LTV:CAC Ratio Calculator by ToolWise Digital.
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