Email And SMS CAC: Counting Owned-Channel Cost Honestly
Email and SMS mostly retain — but they do acquire customers via referrals, re-engagement, and list capture. Here's how to count that CAC without double-billing paid.
Quick answer
Assign email and SMS CAC only to net-new customers those channels genuinely originated: referral opt-ins, re-engaged lapsed buyers (12+ months dormant), and organic list signups that later convert. Amortize the cost of building that list — pop-up tools, welcome-flow discounts, SMS opt-in incentives — over 12 months of new acquisitions. Never claim a customer for email if paid touched them in the same window; give paid the CAC and let email carry retention credit.
Email and SMS CAC (owned-channel)
The blended acquisition cost assigned to email and SMS when those channels originate a net-new customer, adjusted for list-build spend and paid overlap.
Email and SMS are usually retention channels — they re-sell to people you already acquired. But they also produce a smaller stream of net-new customers: a friend forwards a flow, someone opts into SMS via a paid landing page and buys weeks later, or a win-back flow reactivates a customer dormant long enough to count as re-acquired. Honest owned-channel CAC captures those cases without inflating them.
The cost side is trickier than paid. Klaviyo and Postscript fees are minor; the real spend is list-build — welcome discounts, pop-up software, giveaways, and the paid traffic you sent to opt-in pages. Amortized correctly, that gives you a defensible CAC number for owned channels.
Most Shopify brands book 30-50% of revenue through Klaviyo and SMS but call it all retention. That's directionally right — and directionally lazy. Somewhere in that revenue is genuine acquisition that deserves its own CAC line, distinct from Meta or Google.
The point of this exercise isn't to inflate email's contribution. It's to make CAC by channel comparable, so you can decide whether the next euro belongs in paid social, in a referral program, or in a bigger welcome incentive.
What counts as acquisition on email and SMS
Three customer types legitimately belong to owned-channel CAC. First: referral opt-ins — someone forwarded a flow, a friend signed up, and that friend bought. Second: cold list-builders — an Instagram giveaway or content lead-magnet that captured an email address which later converted with no paid retouch.
Third — and this one's contested — re-engagement. If a customer went dormant for 12+ months and a win-back flow brought them back, most finance teams treat that as re-acquisition. Under 12 months it's retention. Pick your threshold and hold it consistent across quarters.
The double-counting trap
If a customer clicked a Meta ad, then opened three welcome-flow emails, then bought — that's a paid acquisition. Full stop. Email gets zero CAC credit and 100% of the assist. Brands who split credit here end up under-reporting Meta CAC by 20-40% and quietly killing profitable campaigns because the dashboard says they're marginal.
Amortizing list-build cost
The honest cost side has three lines: platform fees (Klaviyo, Postscript, Attentive), incentive cost (welcome discount margin loss), and list-build traffic (paid spend routed to opt-in pages rather than product pages).
Amortize list-build over 12 months of email-originated acquisitions, not one. A €4,000 giveaway that captured 8,000 subscribers doesn't cost €0.50 per subscriber — it costs whatever the subscriber-to-customer conversion rate turns it into. If 6% of that list eventually buys via email as the origin channel, effective CAC on that cohort is around €8.30.
Welcome discount margin loss is real cost. A 15% welcome code on a €60 order at 55% gross margin costs you €9 of margin — treat that as a variable acquisition expense on every first purchase that used the code, not a rounding error.
Benchmarks by store type
Owned-channel CAC and acquisition mix by store vertical (Shopify, €2M-€10M annual revenue band)
| Vertical | Email-originated CAC | SMS-originated CAC | % of total acquisition from owned |
|---|---|---|---|
| Apparel | €6-€12 | €9-€15 | 8-14% |
| Beauty & skincare | €8-€14 | €10-€18 | 12-18% |
| Home & lifestyle | €10-€18 | €14-€22 | 6-10% |
| Food & supplements | €7-€11 | €8-€13 | 10-15% |
| Electronics accessories | €12-€20 | €16-€26 | 4-8% |
Beauty and supplements over-index on owned-channel acquisition because giveaway mechanics and referral behaviour work harder in those categories. Electronics under-indexes because the purchase is considered — a welcome flow rarely closes a first-time buyer on a €200 accessory.
Handling overlap with paid channels
The clean rule: paid gets the CAC, owned gets the assist. If Meta acquired the email address and email closed the sale, Meta owns the customer's acquisition line and email carries a separate assisted-revenue metric. This keeps CAC by channel decision-useful for budget allocation.
In practice, tag opt-in source at capture. Klaviyo's source properties and UTMs on your pop-up variants let you split subscribers into paid-sourced vs organic-sourced buckets. Only the organic bucket's downstream conversions belong in owned-channel CAC.
The referral edge case
Referrals are the cleanest source of true email/SMS acquisition. If a customer forwards a welcome flow or shares a discount code via SMS and a new person converts, that customer was born in the owned channel with essentially zero variable cost beyond the referral incentive itself.
Track referral acquisitions separately from the rest of owned-channel CAC — they usually run 40-60% cheaper than any paid channel and disguise your true blended owned-channel efficiency if you lump them in. Break them out; celebrate them; scale the mechanics.
Common questions
Split them. Allocate the portion tied to acquisition flows (welcome series, referral flows, list-build automations) to CAC, and the retention flow portion to opex. A rough 30/70 split acquisition/retention works for most stores under €10M revenue.
Paid CAC divides ad spend by attributed new customers within a defined window. Owned-channel CAC has to amortize list-build spend across future cohorts and explicitly exclude customers whose acquisition should be credited to paid. See CAC by channel for the broader framework.
Most finance teams use 12 months of inactivity as the threshold. Under 12 months, a win-back purchase is retention. Over 12 months, treat them as re-acquired and count the win-back flow's amortized cost against that acquisition.
Take SMS platform fees plus opt-in incentive costs (typically a 10-15% welcome discount) plus any paid traffic sent to SMS-only landing pages. Divide by SMS-originated new customers over a rolling 12 months. Realistic range: €9-€22 depending on vertical.
Only if the pop-up sat on organic traffic. If Meta or Google brought that visitor, paid owns the acquisition and email carries the assist. Tag the pop-up conversion with the visitor's UTM source at capture time to make this split automatic.
Treat the incentive margin loss (usually 10-15% of AOV, times your gross margin) as a variable cost on every first purchase using the code. It's not a rounding item — on a €70 AOV at 50% margin, a 15% welcome code costs €5.25 per first purchase.
No. Klaviyo credits any purchase within its attribution window (default 5 days for email, 1 day for SMS) after a message open or click. That inflates email/SMS revenue by counting sales paid already acquired. Use Klaviyo attribution for flow optimisation, not for CAC.
Track the cohort. If a giveaway added 5,000 subscribers in March, follow that cohort's email-originated first purchases over 12 months. Divide total campaign cost (prize + ad spend + creative) by that cohort's new customers to get true giveaway CAC. Usually €7-€15 per acquired customer.
Rented lists are paid acquisition dressed as owned. The per-message fee plus incentive cost belongs in a paid-channel CAC line, not owned. Only subscribers who opted in directly on your properties count toward true owned-channel CAC.
Quarterly is enough. List-build cohorts take 6-12 months to fully mature (their acquisition tail keeps producing), so monthly numbers are noisy. Quarterly rolls smooth the cohort maturation and let you compare owned CAC against paid channels on a consistent cadence.
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