CAC Checklist for Growth Leads

Define Your Cohort Window

CAC calculation requires a fixed time window. Most teams use 30 - or 90 - day cohorts. The window determines which spend counts and which customers count as 'acquired.'

A 30 - day cohort captures faster feedback but masks seasonal patterns. A 90 - day cohort smooths volatility but delays signal detection. For DTC Shopify brands running continuous campaigns, 30 - day rolling cohorts are standard.

Define cohort start date (e.g., first day of month, campaign launch date)
Define cohort end date (e.g., 30 or 90 days after start)
Lock the window before calculating - retroactive changes destroy comparability
Document the rule in a shared ops doc; enforce it across all reports

Audit Your Spend Bucket

CAC fails when spend definitions drift. Teams often exclude fulfillment, customer service, or platform fees - then wonder why unit economics don't match reality.

Include all costs that directly enable customer acquisition: paid ads, influencer fees, affiliate commissions, email platform costs (if used for acquisition), SMS platform costs (if used for acquisition), and tools (analytics, attribution, CRM). Exclude: COGS, shipping, customer support, content production unrelated to acquisition.

Audit every marketing tool subscription - is it acquisition or retention?
Include platform fees (Shopify Payments processing, ad platform fees)
Separate paid ads by channel (TikTok, Instagram, Google, Pinterest, etc.)
Track influencer spend separately if volume is >10% of total spend
Exclude: product development, general overhead, returns processing

Set Thresholds and Failure Modes

CAC thresholds depend on AOV, margin, and repeat purchase rate. A $50 AOV brand cannot sustain a $30 CAC. A $200 AOV brand with 40% repeat rate can.

The rule: CAC should not exceed 20 - 30% of first - order profit margin for single - purchase categories. For repeat - purchase (subscription, consumables), CAC can run 50 - 100% of first - order profit if LTV supports it.

Calculate first - order profit: AOV - COGS - fulfillment - payment processing
CAC threshold = 20 - 30% of first - order profit (conservative)
If repeat rate >30%, CAC threshold = 50 - 100% of first - order profit
Flag red: CAC >40% of first - order profit for single - purchase brands
Flag red: CAC >120% of first - order profit for repeat - purchase brands
Common failure: ignoring repeat rate and treating all CAC equally

Measure Attribution Accurately

Attribution is where most CAC calculations break. Last - click attribution inflates paid performance. First - click attribution inflates organic. Multi - touch is more honest but harder to execute.

For DTC Shopify brands, first - party data (UTM parameters, Shopify source tracking) is the baseline. Supplement with pixel - based tools (Segment, mParticle) if budget allows. Avoid relying solely on platform attribution (Meta, Google) - it systematically overstates performance.

Enforce UTM tagging on all paid campaigns - no exceptions
Use Shopify's native source tracking as ground truth for organic vs. paid
Audit UTM consistency: same campaign name = same utm_campaign value
If using multi - touch, document the model (linear, time - decay, custom)
Test: compare platform attribution to Shopify source data - flag >20% variance
Do not use platform attribution alone for CAC decisions

Segment CAC by Channel

Aggregate CAC hides channel performance. A brand with $20 CAC might have $12 CAC on TikTok and $35 CAC on Google - the average is useless for optimization.

Segment by paid channel (TikTok, Instagram, Google, Pinterest, email, SMS, affiliate). Track organic separately. This reveals which channels to scale and which to cut.

Create separate CAC calculations for each paid channel
Track organic CAC separately (divide organic marketing spend by organic customers)
Organic CAC should be 30 - 50% lower than paid - if not, organic spend is mislabeled
Review channel CAC weekly - flag channels with rising CAC (signal of saturation)
Do not average channels - compare them

Link CAC to LTV

CAC in isolation is meaningless. A $40 CAC is good if LTV is $200, bad if LTV is $60. The ratio CAC:LTV should inform scaling decisions.

Target CAC:LTV ratio of 1:3 or better (CAC is 1/3 of LTV or less). Ratios below 1:5 indicate underinvestment in acquisition. Ratios above 1:2 indicate overinvestment or weak retention.

Calculate LTV: (AOV × repeat rate) / churn rate, or use 12 - month cohort data
CAC:LTV ratio = CAC / LTV
Target: 1:3 or better (CAC ≤ 33% of LTV)
If ratio >1:2 (CAC >50% of LTV), audit retention or reduce spend
If ratio >1:1 (CAC >100% of LTV), stop scaling - unit economics are broken
Recalculate LTV quarterly - it changes with retention and repeat rate

Audit and Reforecast Monthly

CAC drifts. Platforms change algorithms. Audiences saturate. Spend efficiency declines. A monthly audit catches drift before it compounds.

Run a CAC audit on the first of each month: verify spend bucket, check attribution, recalculate by channel, compare to prior month, flag variances >15%.

Pull spend data from each platform (ads manager, email tool, affiliate network)
Verify new customer count from Shopify (filter by acquisition date, exclude test orders)
Recalculate CAC overall and by channel
Compare to prior month - flag increases >15%
If CAC increased, diagnose: audience saturation, algorithm change, spend shift, or attribution error
Document findings in a shared ops log - reference for Q reviews

Questions

FAQ

Should we include email and SMS platform costs in CAC?

Only if the platform is used for acquisition (welcome series, cold outreach). If it's used for retention (post - purchase nurture, loyalty), exclude it. Most teams use email/SMS for both - in that case, allocate a portion (e.g., 30%) to acquisition based on segment volume.

What's the difference between CAC and ROAS?

ROAS (Return on Ad Spend) is revenue divided by ad spend - it ignores COGS and other costs. CAC is the cost per customer acquired - it's a unit metric, not a return metric. ROAS of 3:1 can coexist with a CAC that's too high if margins are thin. Use both, but CAC is more actionable for unit economics.

How do we handle free trial signups or email captures in CAC?

Only count paying customers as 'acquired.' Free trials and email captures are leads, not customers. If you must track them, calculate a separate metric (Cost Per Lead) and monitor conversion rate from lead to paying customer. CAC should always mean 'cost per paying customer.'

Can CAC be negative?

In rare cases, yes - if a customer refers others or generates affiliate revenue that exceeds their acquisition cost. This is not a failure mode; it's a signal to double down on that cohort or channel. Document it separately and investigate what made it work.

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