Customer acquisition cost tells you what you spend, on average, to win one new customer. It is the number that decides whether your marketing pays, and it only works if you count costs consistently from month to month.
How it works
CAC = total sales and marketing costs / number of new customers acquired in the same period. The numerator should include ad spend, sales salaries and commissions, marketing tools, and agency fees for that period. Whether to include founder time and overhead is a judgement call; the key is to use the same rule every period so trends are comparable. CAC is usually judged against customer lifetime value: a business is sustainable when lifetime value comfortably exceeds CAC.
Step by step
- Choose a period, such as one month or one quarter.
- Add up all sales and marketing costs in that period, using one consistent rule.
- Count only new customers acquired in that period, not returning buyers.
- Divide costs by new customers for CAC.
- Compute payback: months to recover CAC = CAC / monthly gross profit per customer.
- Compare CAC with lifetime value, and track the ratio over time.
Worked example
In one month you spend $12,000 on ads, $6,000 on sales salaries, and $2,000 on tools, totalling $20,000. You acquire 100 new customers. CAC = 20,000 / 100 = $200 per customer. If each customer brings $50 gross profit per month, payback is 200 / 50 = 4 months. If lifetime value is $600, the LTV to CAC ratio is 3 to 1, which is generally considered healthy.
Common mistakes
- Counting returning customers as new, which understates CAC.
- Leaving salaries out of the numerator, which makes CAC look artificially low.
- Mixing periods, such as quarterly spend with monthly customers.
- Comparing CAC across businesses with different numerator rules.
Try it with the free tool
You can follow every step above by hand, but the free tool below does the same calculation instantly. Try your own numbers in it, then check one result by hand so you trust the method as well as the answer. Open the full tool here: open the tool.
Checklist before you finish
- Write down every input number first, with its unit, before you calculate anything.
- Work through the steps in order, and do not skip the unit conversions.
- Check the answer against the worked example above: is it the right size, and does the direction make sense?
- Round only at the end, and keep the unrounded figure for any follow-up calculation.
Practice with your own numbers
Pick three cases of your own and work each one by hand. First, try a simple round-number case you can check mentally. Second, try a realistic case with awkward numbers, the kind you will actually meet. Third, try an edge case, such as a very small or very large input, and confirm the answer still behaves sensibly. If any case gives a surprising result, re-check the units and the formula step by step before you trust it.
If your answer looks wrong
Most errors come from a small set of causes. Check that you used the same units throughout, that you divided where the formula divides and multiplied where it multiplies, and that you applied any percentage as a decimal. Check the order of operations: powers and brackets come before multiplication and division, which come before addition and subtraction. Finally, test the method on the worked example in this guide. If your method reproduces the example answer, the method is right and the inputs deserve a second look.
Quick tips
Split CAC by channel, because a blended CAC hides the fact that one channel may be profitable and another may be losing money. Track CAC monthly; a rising trend is an early warning even while sales still grow.