Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
CAC payback (months)
9.4
Monthly contribution per customer
$96.00
Expected lifespan (months)
40.0
Profit after payback
$2,940
Read
Efficient — pays back inside a year
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How to use this
- 1Enter cac ($).
- 2Enter monthly revenue per customer ($).
- 3Enter gross margin (%).
- 4Enter monthly churn (%).
- 5Read your cac payback (months) on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
Payback measures how fast the cash comes back, which matters more than LTV when you are funding growth from operations. Under 12 months is efficient; over 24 means you need outside capital to grow.
Worked example
Using the values the calculator loads with:
Inputs
- CAC: 900 $
- Monthly revenue per customer: 120 $
- Gross margin: 80 %
- Monthly churn: 2.5 %
Results
- CAC payback (months): 9.4
- Monthly contribution per customer: $96.00
- Expected lifespan (months): 40
- Profit after payback: $2,940.00
- Read: Efficient — pays back inside a year
What each field means
Inputs
- CAC ($)
- The cac used in the calculation, measured in $. Starts at 900 $ so you have a working example on load.
- Monthly revenue per customer ($)
- The monthly revenue per customer used in the calculation, measured in $. Starts at 120 $ so you have a working example on load.
- Gross margin (%)
- The gross margin used in the calculation, measured in %. Starts at 80 % so you have a working example on load. Accepted range: 1–100 %.
- Monthly churn (%)
- The monthly churn used in the calculation, measured in %. Starts at 2.5 % so you have a working example on load. Accepted range: 0.01–50 %.
Results
- CAC payback (months)
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Monthly contribution per customer
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Expected lifespan (months)
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Profit after payback
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Read
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the cac payback period calculator work?
Payback measures how fast the cash comes back, which matters more than LTV when you are funding growth from operations. Under 12 months is efficient; over 24 means you need outside capital to grow. The underlying maths is: Payback = CAC ÷ (ARPU × Gross margin).
What do I need to enter?
4 values: cac, monthly revenue per customer, gross margin, and monthly churn. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the cac payback (months) result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Who is this tool for?
It's built for anyone comparing money scenarios before committing — budgeting a payment, sanity-checking a quote, or seeing what a change in rate or term actually costs.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). CAC Payback Period Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/saas-payback
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/saas-payback" target="_blank" rel="noopener">CAC Payback Period Calculator — RevenueLab</a> (2026).</p>
Source: [CAC Payback Period Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/saas-payback) (2026).