Ecommerce & CRO
CAC
Customer Acquisition Cost
CAC, or customer acquisition cost, is the total sales and marketing spend needed to win one new customer. It is read against LTV: a business whose CAC approaches its LTV is buying revenue at a loss. Rising ad costs are the main reason merchants invest in organic channels such as SEO, where the cost per customer falls over time instead of rising.
Why it matters
CAC is the number that decides whether growth is a business or a subsidy. Paid acquisition costs have risen consistently across most categories, and a model that worked at a £25 CAC does not survive at £45 unless something else changed — margin, AOV, or repeat rate.
The trap is that CAC rises quietly. Campaigns keep running, the ad platform keeps reporting a healthy return, and the blended cost per customer drifts upward month by month without any single decision causing it. Businesses tend to notice when cash gets tight rather than when the trend starts.
This is the entire commercial case for organic channels. Paid CAC rises with competition and with scale; content and SEO cost more up front and less per customer over time, which is the opposite curve. A business with only paid acquisition has no way out of that trend.
How it works on Shopify
The calculation is total sales and marketing spend over a period divided by new customers acquired in it. Both halves need care.
Spend means everything: ad budget, agency fees, tooling, and the salary cost of the people running it. A CAC built on media spend alone is comfortably wrong and usually by a third.
New customers means new, not orders. Shopify distinguishes first-time from returning customers, and mixing them understates CAC by counting repeat purchases as acquisitions.
Blended CAC — all spend against all new customers — is the honest headline. Channel-level CAC is where decisions get made, but platform-reported figures are optimistic: attribution windows overlap, so the channels together claim more customers than the business actually gained. Reconciling platform attribution against Shopify's own new-customer count is what keeps the number defensible.
Read against LTV and payback period. A 3:1 ratio with an eighteen-month payback still leaves a cash flow problem.
Common mistakes
- Counting media spend only. Agency fees and salaries are acquisition costs.
- Trusting platform attribution. Every channel claims the same conversion. Adding them produces more customers than the store had.
- Dividing by all orders. That is cost per order, not per customer, and it flatters the figure by the repeat rate.
- Ignoring payback period. Profitable eventually and solvent now are different questions.
- No organic baseline. Without knowing what customers arrive at zero marginal cost, paid performance cannot be judged.
When you need help
The clearest signal is a business whose revenue is growing while its cash position is not. That gap is nearly always CAC rising faster than margin, and it is visible in the data long before it is visible in the bank.
The other case is reducing dependence on paid acquisition — building the organic and retention channels whose cost per customer falls over time. That is a longer programme than a campaign, and the honest version starts with modelling what the business's CAC will look like in two years if nothing changes.
Related terms
- LTVLTV, or customer lifetime value, is the total profit a business expects from one customer across the whole relationship. It is what justifies acquisition spend: if LTV is $180 and it costs $60 to acquire a customer, the ratio of 3:1 is generally considered healthy. LTV rises with repeat purchase rate, AOV, and margin, and falls with churn.
- ROASROAS, or return on ad spend, is the revenue produced per dollar of advertising — $4 back on $1 spent is a ROAS of 4. It measures campaign efficiency, not profitability: a 4× ROAS on a product with a 20% margin still loses money. Blended ROAS, measured across all spend and all revenue, is harder to game than platform-reported figures.
- Core Web VitalsCore Web Vitals are the three metrics Google uses to score real-world page experience: LCP for loading, INP for responsiveness, and CLS for visual stability. They are measured from actual Chrome users, not a lab test, and a page passes only if 75% of visits are within the "good" threshold on all three. They are a genuine — if modest — ranking signal, and a large conversion one.