Customer Acquisition Cost: How to Calculate It Correctly (Most Don't)

The CAC Calculation Problem

Customer Acquisition Cost (CAC) is one of the most important metrics in any growth business. It's also one of the most frequently miscalculated. Teams undercount costs to make CAC look lower, or use ad spend as a proxy for total acquisition cost. Either produces numbers that lead to bad decisions.

Our marketing analytics team defines CAC consistently as part of every measurement framework we build.

The Correct CAC Formula

CAC = Total Sales and Marketing Spend / New Customers Acquired (same period)

This sounds simple. The complexity is in defining the numerator correctly.

What "Total Sales and Marketing Spend" Must Include

Most teams calculate CAC using only ad spend. This produces a number that's significantly understated. True CAC includes:

Marketing Costs

• Paid advertising spend (Google Ads, Meta Ads, LinkedIn, etc.)
• Marketing team salaries (fully loaded: base + benefits + taxes)
• Agency fees and contractor costs
• Marketing software subscriptions (email platform, CRM, analytics tools, design tools)
• Content production costs
• Event and sponsorship costs
• SEO costs (if outsourced or significant internal time)

Sales Costs

• Sales team salaries (fully loaded) — for the portion of time spent on new acquisition (not renewals)
• Sales software (CRM, outreach tools, proposal tools)
• Sales commissions and bonuses
• Sales training and enablement costs

Blended CAC vs. Channel-Specific CAC

Blended CAC

Total marketing + sales spend / All new customers. This is the most accurate representation of what it actually costs to acquire a customer across your entire go-to-market motion. Use for strategic planning, LTV:CAC ratio calculation, and board-level reporting.

Channel-Specific CAC

Channel spend / Customers attributed to that channel (via GA4 attribution). Less accurate (attribution model dependent) but useful for comparing channel efficiency and making tactical budget allocation decisions.

Channel CAC will always understate true CAC because it only counts the channel spend, not the shared sales and marketing overhead that supports it.

The Time Lag Problem

For B2B businesses with long sales cycles, the costs and customer acquisition happen in different periods. Spend occurs in January to generate leads that close in April. Dividing April's marketing spend by April's new customers produces meaningless numbers.

Solutions:

• Match spend to the period when the leads were generated, not when they closed
• Use a rolling 3–6 month average of both spend and customers acquired
• Track CAC cohorts: what was total spend in the 6 months before a customer cohort closed?

Using CAC to Make Decisions

CAC without LTV context is meaningless. A £500 CAC is excellent if average LTV is £5,000; it's a catastrophe if average LTV is £600.

Always evaluate CAC in context of LTV:CAC ratio (covered in the next article) and payback period (how many months of margin until CAC is recovered).

Connect your ad spend data, GA4 conversion data, and financial data in BigQuery to calculate CAC accurately. Our marketing analytics team builds these data pipelines. Contact us for help setting up accurate CAC tracking.