Customer Acquisition Cost (CAC) Calculator
- No invented stats
- Written for UK readers
- Published 19 September 2026
Add up what you spent on sales and marketing over a period, enter how many new customers you won in that period, and this calculator gives you the cost of acquiring one of them. Add a lifetime value figure and it will also show you the ratio between the two. Nothing you enter is sent anywhere — it all happens in your browser.
How this works
Total sales and marketing spend for a period, divided by the number of new customers won in that period. That is the whole calculation. The difficulty is not the arithmetic — it is deciding what counts as spend.
The fuller the cost, the more useful the answer. A defensible figure includes salaries, commission and employer's National Insurance for everyone in sales and marketing, agency and freelancer fees, advertising, content, events, and the sales and marketing tools you pay for each month. Leaving salaries out is a common way people arrive at a flattering number: if your CAC only counts ad spend, it is measuring your ad efficiency, not your acquisition cost.
Excluded, normally, are the costs of serving customers you already have — support, customer success and account management — along with product development and general overheads. Renewals and upsells are not new customers, so keep the revenue and the customer count consistent: if you count an expansion as a new customer, you have to count the cost of winning it too.
If you provide a lifetime value, the calculator divides it by the CAC to give you a ratio. That ratio, not the CAC on its own, is the number worth looking at. A high acquisition cost is perfectly fine if customers stay for years.
A worked example
A small UK business spends £18,000 on sales in a quarter — one salesperson's salary, National Insurance and commission — and £7,000 on marketing, covering advertising, a freelance writer and its CRM and email tools. In that quarter it wins 20 new customers.
Total spend: £18,000 + £7,000 = £25,000.
Customer acquisition cost: £25,000 ÷ 20 = £1,250.00 per customer.
If the lifetime value of those customers is £9,375, the ratio is £9,375 ÷ £1,250 = 7.5:1. Every £1 spent winning a customer comes back as £7.50 of lifetime gross profit — though spread over the several years that customer stays, which is a cash flow problem as much as a profitability one.
What this doesn't account for
The main flaw is timing. Money spent this quarter often wins customers next quarter, particularly if your sales cycle runs longer than the period you are measuring. Dividing this period's spend by this period's customers quietly assumes the two line up, and they rarely do. If your sales cycle is long, measure over a longer window, or lag the spend by roughly the length of the cycle.
It also blends every channel into one number. A referral that cost you nothing and a customer who came from six months of paid advertising both count as one customer here, which flatters the expensive channel and hides the cheap one. If you can split spend by channel, do — a blended CAC is a reporting number, not a decision-making one.
Nor does it say anything about the quality of what you bought. Twenty customers acquired cheaply who churn within six months are worse than ten expensive ones who stay for years, and CAC on its own cannot see the difference. Always read it next to churn and lifetime value, and be wary of any target that rewards chasing customers who were never a good fit.
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