CAC Payback Period Calculator

Input accuracy

Are you using real, current numbers — not rough guesses that flatter the result?

Benchmark fit

Is your result healthy for your specific business model, not just positive?

Sensitivity

Which single input, if wrong, would change the result most?

Time horizon

Does this hold up over 12 months, or only at today's volume?

Next decision

What should change in the business because of this number?

Payback period answers a question the LTV:CAC ratio cannot: how long is your cash tied up? Money spent acquiring a customer leaves immediately, while the money they generate arrives slowly.

This is why fast-growing companies with healthy ratios still run out of cash. This calculator shows the payback in months and flags whether the average customer churns before they have repaid you.

Free calculator

Find how many months it takes a customer to repay what you spent acquiring them — the number that governs how fast growth consumes cash.

Customer acquisition cost£

Monthly revenue per customer£/mo

Gross margin%

Average customer lifetimemonths

Results

Monthly gross profit per customer£80

Payback period11.3 months

Recovered within customer lifetime?Yes

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Why payback runs on gross profit

A customer paying £100 a month who costs £20 to serve repays acquisition at £80 a month, not £100. Using revenue understates payback by the entire cost to serve, which on thin margins can be most of it.

This calculator applies your gross margin before calculating, so the figure reflects money actually available to repay the acquisition cost.

Payback longer than customer lifetime

If payback takes 18 months and the average customer stays 12, every customer is a structural loss no volume can fix. The calculator flags this explicitly, because it is the single clearest signal a model does not work.

Why payback governs growth speed

Every new customer is a cash outflow first and an inflow later, so growth consumes working capital until payback completes. Faster payback recycles capital into the next customer without external funding — which is why it constrains how fast you can grow more directly than the LTV:CAC ratio does.

How this calculator works

Enter your customer acquisition cost, including salaries and tools.
Enter monthly revenue per customer and your gross margin percentage.
Enter average customer lifetime in months (1 ÷ monthly churn).
The calculator returns monthly gross profit per customer, payback in months, and whether it lands inside the customer's lifetime.

Direct answer — CAC Payback Period Calculator

Calculate how many months it takes a customer to repay their acquisition cost, and whether they churn first. Free, no signup.

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Frequently asked questions

What is a good CAC payback period?

Under twelve months is the standard SaaS benchmark, and under six is strong. Enterprise businesses often accept longer paybacks because contract values are larger and retention is higher.

Why use gross profit instead of revenue?

Because only the profit is available to repay acquisition cost. A customer paying £100 a month who costs £20 to serve repays at £80 a month, so using revenue understates payback by a fifth.

What if payback is longer than customer lifetime?

Then each customer loses money and growth accelerates the losses. Either acquisition cost has to fall, price or margin has to rise, or retention has to improve — more volume will not fix it.

Last reviewed 8 August 2026