The CAC formula
CAC = total sales and marketing costs ÷ number of new customers won
Example: in a quarter you spend £6,000 on ads, SEO, your website retainer and the time spent following up leads, and you win 40 new clients. Your CAC is £6,000 ÷ 40 = £150.
Include every cost that goes into winning customers: advertising, agency and freelancer fees, software, and a fair share of staff time. Leaving costs out makes CAC look better than it is.
CAC vs cost per acquisition (CPA)
The two are often confused. Cost per acquisition (CPA) is usually a channel-level measure, such as what you pay Google Ads per lead or per booking. CAC is the full cost of winning a paying customer across all channels. A low CPA on leads can still hide a high CAC if most of those leads never become customers.
Why CAC matters
CAC only makes sense next to what a customer is worth. If an average client is worth £1,200 over their time with you and costs £150 to win, you have room to grow. If they are worth £180, every new customer barely pays for itself. Knowing both numbers tells you how much you can afford to spend on marketing, and where.
How CRO lowers your CAC
There are two ways to reduce CAC: spend less, or win more customers from the same spend. Conversion rate optimisation does the second. If your website turns 2% of visitors into enquiries instead of 1%, every pound spent bringing people to the site produces twice as many leads, without increasing the budget.
The biggest CAC improvements usually come from:
- a higher website conversion rate
- landing pages that match your ads, so paid clicks are not wasted
- better lead quality, so sales time goes on the right people
- faster follow-up on enquiries
- tracking that shows which channels actually produce customers, not just clicks (see UTM parameters)
Common mistakes
- Calculating CAC from ad spend alone.
- Comparing channels by cost per lead without checking which leads become customers.
- Cutting marketing spend to lower CAC, when improving conversion would protect growth.
Related terms
How WebManics can help
We connect GA4 and HubSpot so you can see which channels and pages produce real enquiries, then improve the website so the same budget brings in more of them. Start with a free website conversion audit, or see how our CRO Growth Retainer works.
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