A £30 customer acquisition cost can be excellent for one eCommerce brand and a serious problem for another. The difference is not your click-through rate. It is your margin, repeat purchase behaviour, fulfilment costs and the amount of profit left after the first order. This guide to customer acquisition costs is built for brands that want paid media to produce profitable growth, not attractive-looking platform reports.
What customer acquisition cost actually measures
Customer acquisition cost, usually shortened to CAC, is the total amount you spend to acquire one new customer. At its simplest:
CAC = total acquisition spend / number of new customers acquired
If you spend £20,000 on paid media in a month and acquire 500 genuinely new customers, your CAC is £40.
That calculation is simple. The useful version is not. A platform can report 700 purchases while your business acquires far fewer new customers because existing customers have returned, attribution has overlapped between channels, or discount-led traffic has inflated conversion volume. For management decisions, CAC needs to reflect actual new-customer growth rather than every sale credited by an ad platform.
For an established retailer, the core question is not, “Can we get purchases at this CPA?” It is, “Can we acquire the right new customers at a cost that leaves room for profit and future growth?”
A guide to customer acquisition costs that starts with margin
Setting a CAC target before understanding contribution margin is how brands scale unprofitable campaigns with confidence. Revenue is not profit, and return on ad spend is not automatically a green light.
Start with the first-order contribution available to pay for marketing. Take net revenue, then subtract product cost, shipping and fulfilment, payment fees, returns allowance, packaging, discounts and any variable operational costs tied to the order. What remains is your contribution before acquisition spend.
Consider a brand with a £100 average order value. After VAT, cost of goods, fulfilment, transaction fees and an expected returns provision, it may have £32 left before advertising. A £25 CAC leaves £7 of first-order contribution. A £40 CAC does not become acceptable because Google Ads reports a 2.5x ROAS. It only works if the brand can reliably recover that deficit through repeat purchasing at a known, healthy margin.
This is where many account structures fail. Bidding targets are often selected because they sound efficient, or because they match a previous agency report. They should be derived from commercial reality. Your allowable CAC is a financial decision first and a media-buying decision second.
First-order profit versus lifetime value
There are two valid ways to set CAC limits, but they require different levels of proof.
A first-order profitable model aims to recover acquisition cost from the initial sale. It is more conservative, protects cash flow and is particularly sensible for brands with low repeat rates, seasonal products or volatile stock availability. The trade-off is that you may bid less aggressively than competitors and sacrifice some volume.
A lifetime-value model allows a higher first-purchase CAC because customers repurchase, subscribe or buy higher-margin products later. This can be the right model for consumables, beauty, supplements, pet products and other categories with demonstrated retention. But projected lifetime value is not permission to spend freely. Use realised cohort data: repeat purchase rate, time to second order, gross margin on repeat orders and refund behaviour. If it takes nine months to recover CAC, your cash position must support nine months of payback.
A sensible target also needs a payback window. A brand may accept a £60 CAC if it recovers that spend within 60 days, but reject the same CAC if recovery takes a year. Growth funded by slow, uncertain payback can place unnecessary pressure on inventory and working capital.
What to include in CAC calculations
For channel optimisation, you may track paid CAC using advertising spend divided by new customers from paid activity. For board-level planning, use fully loaded CAC. Both have a place, as long as the distinction is clear.
A fully loaded figure can include:
- Google Ads, Meta Ads, Microsoft Ads and other paid media spend
- Agency or in-house management costs
- Creative production, photography and video costs used for acquisition
- Landing-page, feed-management and conversion-rate optimisation costs
- New-customer incentives, affiliate fees and acquisition-specific software
Do not force every business overhead into CAC. Warehouse rent and customer service salaries exist whether you run ads or not. The objective is a number that helps you make better acquisition decisions, not a bloated metric with no operational value.
Consistency matters more than theoretical perfection. If creative costs are included one month and excluded the next, the trend tells you nothing. Define the calculation, document it and use the same method when comparing channels, campaigns and time periods.
Avoid the attribution traps
Google and Meta are designed to claim credit for conversions. That is useful for optimisation, but dangerous when treated as a complete account of demand generation.
A customer may see a Facebook ad, search for your brand two days later and purchase through a branded Google campaign. Both platforms may report a conversion. Your analytics platform might assign the sale differently again. If you add every reported platform conversion together, you can create a fantasy version of performance.
Use platform data to make in-platform decisions. Google Shopping search-term data, product-level performance and campaign signals are essential when reallocating budget. Meta’s creative and audience signals matter when scaling prospecting. But validate overall efficiency against business data: total new customers, total marketing spend, blended revenue, contribution margin and cash collected.
Blended CAC is particularly valuable when budgets increase. Calculate total acquisition investment across relevant channels, then divide it by total new customers over the same period. If spend rises by 40% but new customers rise by 10%, your blended CAC is telling you something that a single campaign dashboard may hide.
Brand search needs special care. It often converts cheaply because demand already exists. Protecting branded traffic can be commercially sensible, especially against competitors, but it should not be mistaken for new demand creation. Separate brand and non-brand reporting so your prospecting activity is judged honestly.
Use CAC to decide where budget goes
CAC is not a scorecard to review at month-end. It should guide budget allocation every week.
Start by segmenting performance by channel, product category, new versus returning customer, geography and campaign intent. A low CAC from clearance products may look efficient while training customers to wait for discounts. A higher CAC on a flagship product may be more valuable if it introduces customers to the range and produces stronger repeat revenue.
Product feeds matter here. Shopping and Performance Max campaigns cannot overcome poor product data indefinitely. Weak titles, missing attributes, inconsistent pricing and disapproved items restrict reach and waste budget. Before increasing spend, ensure the feed gives the platforms accurate product information and that the products being promoted can support the required CAC.
Then scale in controlled increments. A campaign that works at £200 per day may deteriorate at £800 because it exhausts high-intent demand or broadens into weaker traffic. Increase budget, watch marginal CAC rather than average CAC alone, and give the system sufficient time to generate meaningful data. Aggressive scaling without margin discipline is simply a faster route to wasted spend.
When a high CAC is not the real problem
A rising CAC does not always mean your media buying has failed. It may reveal a conversion problem, a stock issue or a commercial decision outside the ad account.
If traffic quality is stable but conversion rate falls, inspect site speed, mobile checkout, delivery messaging, product-page clarity and stock availability. If a bestseller goes out of stock, the replacement product may naturally convert at a lower rate. If you raise prices, CAC can remain unchanged while ROAS falls, yet contribution per order may improve. That is why profitability analysis must sit above platform targets.
Seasonality changes the picture too. During peak trading periods, auction prices often rise, but higher conversion rates and larger baskets can justify them. A rigid year-round CAC ceiling may cause you to underinvest when demand is strongest. Set targets by season, category and trading objective, then revisit them as margins or repeat behaviour change.
The right acquisition cost is not the lowest possible number. It is the highest cost you can pay repeatedly while protecting contribution, cash flow and the quality of customers entering the business. Once that number is clear, paid media becomes less about chasing cheap clicks and more about buying profitable scale with intent.