The average cost to acquire one new customer when total sales and marketing spend is divided by every new customer won in the period — across all channels, paid and organic alike.
Blended CAC = total sales & marketing spend ÷ total new customers acquired (all channels)
In one quarter you spend £18,000 on sales and marketing — £9,000 on paid ads, £6,000 on salaries, £3,000 on content and tools — and win 120 customers: 45 from paid ads, 75 from organic and referrals.
£18,000 ÷ 120 = £150 blended CAC. Paid CAC = £9,000 ÷ 45 = £200 — a 33% gap the blended average hides.
Blended CAC takes your fully loaded sales and marketing spend — ad budgets, marketing and sales salaries, agency fees, content, tools — and divides it by every new customer acquired in the period, whether they arrived via paid ads, organic search, referrals, or word of mouth. Its counterpart, paid CAC, isolates paid spend and divides it only by the customers attributed to paid channels.
The classic mistake is using blended CAC to make paid-spend scaling decisions. Organic and referral customers have near-zero marginal cost, so they dilute the average: blended CAC can hold steady, or even fall, while the cost of each additional paid customer quietly climbs. A founder who scales ad spend because the blended number looks fine can be funding a channel that stopped working months ago.
For company-level unit economics — the LTV:CAC ratio and CAC payback period — blended CAC is the honest input, because organic is never actually free. The writer producing your SEO content, the developer building your free tool, and your own founder-led sales hours all sit inside sales and marketing spend, so dividing that full cost across all customers reflects what acquisition genuinely costs the business.
Investors often use a related but different measure: the blended CAC ratio, defined as sales and marketing spend per £1 (or $1) of new-plus-expansion ARR rather than per customer. Expansion revenue from existing customers is cheaper to win than brand-new logos, so the blended ratio flatters companies with strong upsell. Know which definition is on the table before you compare numbers.
Blended CAC is the number that belongs in your LTV:CAC ratio, your CAC payback calculation, and your board deck — it captures what acquisition truly costs, including the "free" channels that still consume salaries and time. The gap between blended and paid CAC is also an early-warning system: if blended looks healthy while paid deteriorates, organic growth is masking an inefficient paid engine.
Benchmarkit's 2025 B2B SaaS benchmark report puts the median blended CAC ratio at $1.40 of sales and marketing spend per $1.00 of new-plus-expansion ARR in 2024 (down from $1.61 in 2023), while the median cost of acquiring $1.00 of ARR from brand-new customers alone rose to $2.00.
Blended CAC divides total sales and marketing spend by every new customer from every channel, including organic and referral. Paid CAC divides only paid-channel spend by customers attributed to paid channels. Blended answers "what does a customer cost this business?"; paid answers "is my ad spend working?" You need both.
Divide your fully loaded sales and marketing spend for a period — ads, salaries, agencies, content, tools — by the total number of new customers acquired in that period, regardless of channel. If your sales cycle is long, match spend from the earlier period against the customers it produced.
There is no universal figure — it scales with your price point and sales motion. Judge it relative to value instead: an LTV:CAC ratio of roughly 3:1 or better and a CAC payback period under about 12 months are the standard health checks.
Because near-zero-cost organic and referral customers pull the average down, blended CAC can stay flat while the marginal cost of each additional paid customer rises sharply. Relying on it for channel and scaling decisions hides a deteriorating paid engine — track paid CAC alongside it.
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