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CAC Payback Period Calculator

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How do you calculate CAC Payback Period?

CAC payback period is the number of months a customer's gross margin must run before it repays what you spent acquiring them. It is the cash-flow companion to the LTV:CAC ratio: the ratio says whether acquisition is profitable eventually, payback says how long your cash is locked up getting there, and only one of those determines whether growth can fund itself.

CAC payback period

5.2

Months of gross margin needed to repay acquisition cost.

Monthly contribution per customer: $96ARPU after the cost of serving. This is what actually pays back CAC.
Year-one net contribution: $652Twelve months of contribution less CAC. Negative means the customer has not broken even within a year.

Results are rounded for display; the calculation runs at full precision.

The maths

How CAC Payback Period is calculated

The formula this calculator runs, written out so you can check it against your own model rather than trust a black box.

Payback months = CAC ÷ (ARPU × Gross margin)

CAC: Fully loaded acquisition cost per customer: all sales and marketing spend, including salaries and commission, divided by new customers won.
ARPU: Average monthly recurring revenue per customer. For annual contracts, use the monthly equivalent rather than the invoice amount.
Gross margin: Share of revenue remaining after the direct cost of serving the customer. Omitting it is the most common error in this calculation and shortens apparent payback by 20–40% for typical SaaS margins.

Reading the result

What the number is telling you

Bands are directional, not verdicts. Stage, price point and contract length move every one of them, so treat these as a starting point for the conversation rather than a grade.

Under 6 months: Efficient enough that growth can plausibly fund itself: each cohort repays fast enough to finance the next. Common in low-touch self-serve products. The constraint on growth is channel capacity rather than capital, so the question becomes how much more you can spend before efficiency degrades.
6–12 months: The standard healthy band for SMB and mid-market subscription businesses, and the range most venture-backed companies target. Growth still consumes cash, but at a rate a normal funding cycle can carry. Watch the trend more than the level — payback drifting upward is an early signal of channel saturation.
12–18 months: Workable with capital and low churn, punishing without both. More than a year of a customer's life goes to repaying their own acquisition, so retention becomes the binding constraint. Sustainable mainly for annual contracts where the cash arrives upfront even though the margin does not.
Over 18 months: A large share of customers churn before repaying acquisition. Defensible mainly for enterprise deals with multi-year commitments and strong expansion, where net revenue retention above 100% means the customer's contribution grows rather than merely persisting. Otherwise this is a signal to reprice or change channel.
Returns 0: Monthly contribution is zero or negative, so acquisition is never repaid at any horizon. Either gross margin is at or below zero, or ARPU is missing. The customer loses money on every month they stay, which makes retention a liability rather than an asset.

Gross margin, not revenue

The widely quoted version of this metric divides CAC by monthly revenue, which answers a question nobody has: how long until the customer has been billed enough to cover acquisition. What matters is when the cash you spent comes back, and only the margin portion of revenue is ever available to do that.

The distortion is proportional to your cost of service. At 80% gross margin, revenue-based payback understates the true figure by 20%; at 60% margin, by 40%. For a company deciding whether growth can be self-funded, that gap is the difference between a plan that works and one that quietly requires a raise.

Payback and churn interact, and the interaction is unforgiving

Payback assumes the customer stays long enough to repay you. If monthly churn is 5%, the average customer lifetime is 20 months — a 14-month payback means roughly two thirds of the customer's economic life is spent repaying acquisition, and a meaningful share of the cohort leaves before breaking even at all.

Comparing payback against the implied lifetime from the LTV calculator is the fastest sanity check available. When payback exceeds about a third of the implied lifetime, the LTV:CAC ratio is doing a lot of work on the strength of customers who statistically will not be there.

Annual prepayment changes the cash, not the metric

Collecting twelve months upfront transforms the cash position: the acquisition cost is recovered on day one rather than over five or fourteen months, which is precisely why annual plans are worth discounting for. It does not change the contribution-margin payback period, which measures earned margin rather than collected cash.

Track both, and be explicit about which one you are quoting. Cash payback tells you whether growth is self-funding, and it feeds directly into burn rate and runway. Margin payback tells you whether the customer is economically worth acquiring at all — a customer who prepays annually and churns at renewal has an excellent cash payback and terrible economics.

Definition

Where CAC Payback Period gets argued about

A calculator settles the arithmetic, not the definition — and the definition is where most disagreements about this number actually live. The glossary entry covers the conventions, the edge cases and how Bastle handles each one.

Read the CAC Payback Period definition Browse the metric glossary

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Frequently asked questions

Should CAC payback use revenue or gross margin?

Gross margin. Only the margin portion of a customer's revenue is available to repay what you spent acquiring them; the rest goes to serving them. Using raw revenue understates payback by the inverse of your margin — 20% for a business at 80% gross margin, 40% at 60% — which is frequently the difference between growth that funds itself and growth that requires a raise.

What is a good CAC payback period?

Under twelve months is the usual target for SMB and mid-market subscription businesses, and under six months is efficient enough that acquisition can largely fund itself from the previous cohort. Enterprise businesses with multi-year contracts and strong expansion routinely run longer and remain healthy. The level matters less than its relationship to churn: payback should be a small fraction of your average customer lifetime.

Does annual billing shorten the payback period?

It shortens cash payback dramatically and leaves margin payback unchanged. Collecting twelve months upfront recovers the acquisition cost immediately, which is why annual plans are worth a discount and why they extend runway. The contribution-margin figure this calculator returns measures earned margin over time, so it is unaffected. Quote both, and always say which one you mean.

Should expansion revenue count toward payback?

It can, but it changes what the metric tells you. Including expansion produces a shorter, more accurate payback for businesses with strong net revenue retention, at the cost of blending acquisition performance with account-management performance. The common compromise is to calculate payback on entry ARPU for channel decisions, and a separate expansion-inclusive figure for board reporting, clearly labelled.

How does payback relate to the LTV:CAC ratio?

They measure the same trade on different axes. LTV:CAC asks whether a customer is worth more than they cost, over their whole life. Payback asks how long the cash is tied up before you find out. A business can post a strong 5:1 ratio and still be unable to grow without raising, because the return arrives over three years. Read them together — the ratio for whether to acquire, payback for how fast you can.

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