Calculating Customer Acquisition Cost (CAC)

Calculating Customer Acquisition Cost (CAC): Understanding Your Marketing ROI

Introduction

Marketing decisions made without data are essentially guesses with professional-sounding justification. The most fundamental marketing data point for any service business is Customer Acquisition Cost: the average amount spent on marketing and sales activities to win one new customer.

Without knowing your CAC, you can't answer the questions that matter: Is my Google Ads spend profitable? Should I invest more in SEO or more in paid advertising? Is the Checkatrade listing worth its annual fee? Is the referral programme generating customers at an acceptable cost?

With a calculated, tracked CAC — compared against customer lifetime value — every marketing budget decision becomes rational and evidence-based.

The Basic CAC Formula

CAC = Total marketing and sales spend ÷ Number of new customers acquired

In a given month, if you spend £2,000 on marketing (Google Ads, SEO agency, directory listings) and acquire 10 new customers, your CAC is £200.

This is the starting point. The useful analysis is in the detail.

What to Include in Your Marketing Spend for CAC Calculation

Direct channel costs:

• Google Ads spend (total cost per campaign)

• Meta Ads spend (Facebook and Instagram)

• SEO agency retainer (or your time cost if done in-house)

• Directory listing fees (Checkatrade, Rated People, TrustATrader)

• Leaflet printing and distribution

• Local newspaper or radio advertising

Platform and tool costs:

• Website hosting and maintenance

• CRM software (attributed to marketing if it's primarily a lead management tool)

• Email marketing platform

• Review management software

Internal time costs: Often omitted but genuinely significant: the time you or your team spend on marketing activities — writing content, managing social media, responding to reviews, attending networking events. Estimate this at your effective hourly rate and include it.

Referral programme costs: If you run a referral reward programme, include the cost of rewards paid out.

Channel-Specific CAC: Where the Real Insight Lives

An aggregate CAC tells you your average acquisition cost. Channel-specific CAC tells you which channels are working and which aren't.

Calculate CAC separately for each marketing channel:

Google Ads CAC: Total Google Ads spend ÷ New customers attributed to Google Ads

SEO CAC: Monthly SEO investment (agency cost + content cost + tool cost) ÷ New customers from organic search

Referral CAC: Total referral programme costs ÷ New customers from referrals (usually very low — making referrals a high-ROI channel)

Directory CAC: Annual directory listing fee ÷ New customers from directory (often surprisingly low per customer, but the conversion quality varies significantly)

This requires lead source tracking. Your CRM or enquiry forms should capture how new customers found you. "How did you hear about us?" is the minimum — for accurate channel attribution, use UTM parameters in URLs for digital channels and unique phone numbers for different advertising sources.

CAC Benchmarks for UK Service Businesses

CAC varies significantly by trade type, geographic market, and service complexity. Rough benchmarks:

• Emergency services (24-hour plumbing, locksmithing): £30–£80 CAC (high urgency, fast decision, competitive market)

• Planned trade services (boiler installation, rewires, landscaping): £80–£250 CAC (longer consideration, higher value)

• Recurring service contracts (cleaning, maintenance): £50–£150 CAC (higher upfront investment justified by CLV)

• Commercial services (B2B): £150–£500+ CAC (longer sales cycles, higher values)

These are wide ranges because market competitiveness, geographic location, and individual channel mix all affect CAC significantly. Your benchmark is your own historical CAC compared over time.

CAC in Context: The CAC:CLV Ratio

CAC in isolation tells you less than CAC relative to Customer Lifetime Value (CLV). The ratio that matters:

Healthy CAC:CLV ratio for service businesses: 1:3 minimum, 1:5+ strong

If your CAC is £100 and your average customer generates £300 in lifetime revenue (one job, no repeat), the margin after acquisition cost may not be profitable. If that same customer generates £1,500 in lifetime revenue (repeat jobs + referrals), a £100 CAC is an excellent investment.

This is why retention strategy (addressed in our Customer Retention Strategies guide) directly improves your CAC economics: as CLV increases, the same CAC becomes more profitable.

Reducing CAC: Where to Focus

Improve conversion rate on existing traffic: A higher conversion rate from website visitors to enquiries reduces your effective CAC from SEO and paid channels without reducing spend.

Invest in referral generation: Referral CAC is typically 70–80% lower than paid channel CAC. Systems that generate consistent referrals (referral programmes, post-job review requests, partnership agreements) improve overall CAC significantly.

Reduce wasted spend on unqualified traffic: Poor keyword targeting in Google Ads, or directory listings in categories you don't serve, generates enquiries that don't convert. Eliminating this waste reduces spend without reducing acquired customers.

Improve speed to lead: Faster response to enquiries increases conversion rate from the same enquiry volume, reducing effective CAC.

Conclusion

Knowing your CAC — overall and by channel — transforms marketing budget decisions from gut feeling to evidence. It tells you where to invest more, where to cut, and how your marketing efficiency is trending over time. Calculate it this month. Compare it in three months. Let the data guide your allocation.

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