How do I measure CAC by channel with attribution data?

To measure CAC by channel using attribution data, you want to connect spend to new customers attributed to each channel.

Basic formula

For each channel:

CAC by channel = Channel spend / Number of new customers attributed to that channel

Example:

• Paid Search spend = $20,000
• Attributed new customers from Paid Search = 100
• CAC = $200

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Step-by-step approach

1) Define the time window

Pick a consistent period:

• weekly
• monthly
• quarterly

Make sure both spend and attribution are measured over the same window.

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2) Collect channel spend

For each channel, gather total spend:

• ad spend
• agency fees
• platform fees
• creative costs, if you include them in CAC

Decide whether CAC should include:

• media only
• fully loaded channel costs

Be consistent across channels.

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3) Get attributed conversions / new customers

From your attribution system, pull:

• first-touch conversions
• last-touch conversions
• multi-touch credited conversions
• or whatever attribution model you use

Important: for CAC, use new customers, not just leads or conversions, unless your business defines CAC at lead level.

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4) Match attribution model to the business question

Different models answer different questions:

• First-touch CAC: cost to acquire customers first influenced by the channel
• Last-touch CAC: cost to acquire customers last influenced by the channel
• Multi-touch CAC: cost based on fractional credit across channels

If you use multi-touch attribution, a customer may count partly in several channels. In that case:

CAC for channel = channel spend / attributed customer equivalents

For example:

• Channel gets 40 credited customers
• Spend is $8,000
• CAC = $200

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5) Avoid double counting

If a customer interacted with multiple channels:

• Don’t count them as a full customer in every channel unless using a model that explicitly assigns full credit to multiple channels
• Prefer fractional credit when using multi-touch data

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Example table

Channel	Spend	Attributed New Customers	CAC
Paid Search	$20,000	100	$200
Paid Social	$15,000	75	$200
Email	$5,000	50	$100
Organic Search	$0	80	$0

Note: Organic Search usually has no direct media spend, so CAC may look artificially low unless you include SEO/content costs.

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Best practices

Use the same attribution model consistently

Changing models makes CAC trends hard to compare.

Separate acquisition from retention

Exclude returning customers if you want true acquisition CAC.

Use cohort timing carefully

Spend today may create customers later. If possible:

• attribute based on conversion date
• or use lagged/cohort analysis

Include all relevant costs

If you want true CAC, include:

• media spend
• tools/platforms
• salaries or contractor costs
• creative/production
• sales costs, if applicable

Then you may calculate:

• blended CAC
• channel CAC
• fully loaded CAC

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Common pitfalls

• Using leads instead of customers
• Mixing attribution windows across channels
• Counting attributed conversions without deduping customers
• Comparing channels with different conversion lag using the same same-day window
• Treating fractional attribution like full conversions

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Useful variants

Blended CAC

Total acquisition spend / total new customers

This is helpful as a company-wide benchmark.

Incremental CAC

If you have lift or experiment data, this is better than attribution alone because attribution does not always equal causality.

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If you want, I can also give you:

1. a spreadsheet template,
2. a SQL example, or
3. a method for first-touch vs multi-touch CAC.