Maximum profitable CAC calculator
How much you can afford to pay for a customer without giving up your profit.
≈ 3 minutes
Work out my maximum CAC
Months it takes to recover your CAC
A profitable acquisition cost can still drain your cash. That a customer eventually pays for themselves says nothing about when, and the gap between paying for advertising today and recovering it eight months from now is measured in payroll. This calculator turns your CAC and monthly contribution into a concrete timeframe.
Every calculation runs in your browser. The figures you type are never sent to a server and are never stored.
Your results will appear here
Pick a calculation mode and enter the customer acquisition cost.
- Acquisition cost per customer
- Monthly contribution, or the inputs to derive it
- Payback target, if you have one
Calculation results
Months to recover CAC
—
How long a customer takes to pay back what it cost to acquire them.
In days—
Monthly contribution—
Contribution needed—To meet your target
Difference against target—Months
Contribution difference—
Does it meet the target?—
See the breakdown
| Acquisition cost | — |
| Monthly contribution | — |
| Payback months | — |
| Payback days | — |
| Target in months | — |
| Contribution needed | — |
Recommended next step
If the period is longer than your cash can carry, the fastest lever is paying less per sale: start by knowing which advertising return leaves you at break-even.
Work out my break-even ROASResults are estimates based on the information you enter. Fees, taxes and platform terms can change: always check the figure that matters to you against your invoice or the official platform. They do not replace your real invoices, your official accounts or professional tax, financial or legal advice.
What this tool works out
This CAC payback period calculator answers a treasury question, not a profitability one: how long passes between paying to acquire a customer and that customer having returned the money.
They are two independent questions and worth keeping apart. A customer can be enormously profitable over two years and still wreck your cash flow if recovery takes ten months. The shorter the period, the sooner you can reinvest the same dollar in winning the next one.
Quick mode and detailed mode
The calculation needs the customer's monthly contribution: what they leave each month after every variable cost of their orders. You can supply it two ways.
In quick mode you enter it directly, because you have already worked it out. In detailed mode it is derived from three figures that are usually closer to hand: average order value, how many times they buy per month, and what percentage of contribution each order leaves.
Both modes land in the same place. The detailed one only saves you doing the multiplication elsewhere, with the advantage of exposing which of the three factors you are assuming on the thinnest evidence.
How the formula works
Payback is a simple division; the rest is conversion and comparison.
In detailed mode:
monthly contribution = average order x orders per month
x contribution margin % / 100
payback in months = CAC / monthly contribution
payback in days = months x 30.4375
With a payback target:
required contribution = CAC / target months
month difference = actual months - target months
Days come from multiplying by 30.4375, which is 365 days spread across twelve months. Not a thirty-day month nor a thirty-one-day one: the average calendar month.
A worked example
Acquiring a customer costs $45. In detailed mode: their average order is $55, they buy 1.4 times a month, and each order leaves 30 % contribution. The store has set a 3-month payback target.
| Item | Value |
|---|---|
| Acquisition cost | $45.00 |
| Customer monthly contribution | $23.10 |
| Payback in months | 1.95 |
| Payback in days | 59.3 |
| Payback target | 3.00 |
| Contribution needed for the target | $15.00 |
| Contribution to spare | $8.10 |
The customer leaves $23.10 a month, so the investment returns in 1.95 months: about 59 days. The 3-month target is met with room to spare, and hitting it exactly would need only $15 of monthly contribution instead of the current $23.10.
How to read the result
There is no universally good payback period. What makes one good or bad is the cash you have to sustain it: a business with a cushion can afford six months; one funding this month's advertising from last month's sales needs to recover in weeks.
The figure that really matters is the relationship between the period and your cash cycle. Recover CAC in two months and every dollar invested in acquisition can work six times a year. Take eight, and that same dollar barely works one and a half times.
When there is a target, the required contribution is the direct lever: it tells you how much the customer would have to leave each month to meet the deadline you set. Comparing it with the real figure points at whether the problem is price, purchase frequency or margin.
When no payback is possible
If monthly contribution is zero or negative, there is no period at all: the customer never returns the investment because every month they keep buying subtracts instead of adding. The calculator flags that rather than returning a huge number that looks like a long period.
That case is not fixed by waiting. It is fixed in the price, in the variable costs of the order or in purchase frequency, and until it is fixed every new customer deepens the loss.
What to decide next
If the period is longer than your cash can carry, the fastest lever is not the customer but the bid: lowering cost per acquisition shortens the period immediately, without touching price or waiting for anyone to buy more often.
What this assumes
- Monthly contribution stays constant across the period
- The customer keeps buying at the rate you entered
- One month equals 30.4375 days, the average calendar month
- The time value of money is not discounted
- The CAC is paid in full at the moment of acquisition
What it does not cover
- Whether the customer is profitable long term, which is a different question
- Customers churning before the period completes
- Seasonality in purchase frequency
- The financing cost of advancing the investment
- Payback differences between acquisition channels
Frequently asked questions
Which monthly contribution do I enter?
What the customer leaves each month after every variable cost of their orders: product, shipping, packaging, fees and returns. Not what they bill and not their gross margin. Revenue is always larger than contribution, so using it shortens the period and makes you believe you recover sooner than you do.
What counts as a good payback period?
Whatever your cash can carry. There is no universal figure: a business with a cushion can sustain six months, another reinvesting each month's revenue needs weeks. The useful comparison is against your own treasury, not an industry average.
How is this different from maximum CAC?
Maximum CAC says how much you can pay; this says when you get it back. They are independent: a CAC that is perfectly sustainable over twelve months can leave you illiquid if recovery takes eight. One question is about profit, the other about cash.
Why is a month 30.4375 days?
Because that is the real average month: 365 days divided by twelve. Using 30 days would artificially shorten the period and 31 would stretch it. With the average month, the days and months the calculator returns are consistent with each other.
Which mode should I use, quick or detailed?
Quick if you already have monthly contribution per customer. Detailed if average order, frequency and margin are easier to supply: they reach the same result, but detailed exposes which factor you are assuming on the least data.
What if the customer stops buying before the period ends?
The calculation assumes they keep buying at the rate you entered, so early churn stretches the real period or makes it impossible. If your churn is high, use a prudent purchase frequency rather than the one your best customers show.
Does it work if my customer buys only once?
Not directly: this calculator assumes a monthly contribution that repeats, so its ratio does not describe the calendar of a one-off purchase. With a single purchase, compare that order's contribution against the CAC directly. If it covers it, payback happens with that purchase. If it does not and no further purchases follow, it never happens.
What should I work out after this?
The minimum return your advertising needs. If the period is longer than you can carry, paying less per sale shortens it immediately, and for that you need to know which ROAS leaves you at break-even.
Official sources
Shopify — CAC payback periodhttps://www.shopify.com/blog/cac-payback-period
Shopify — ecommerce customer acquisition and cost per customerhttps://www.shopify.com/blog/ecommerce-customer-acquisition
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