Quick answer: Blended CAC divides ad spend by every purchase, repeat customers included. New customer CAC divides it by first-time buyers only. If a good share of your Meta purchases come from people who already bought, blended CAC looks healthier than what it costs to find a new customer.
Reach and frequency show how ads are delivered. They cannot tell you whether the people reached were new. Your store data can.
Two CACs
| Blended CAC | New customer CAC | |
|---|---|---|
| Formula | Spend / all purchases | Spend / first-time customers |
| Source | Ad platform | Your store |
| What it tells you | Platform efficiency | Cost of adding a customer |
| Use it for | Day to day optimization | Targets and payback |
Only a new customer has an acquisition cost to pay back.
An illustrative example
Take an illustrative account (ratios modelled on a real account we audited). Spend of about ₹6 lakh produced about 2,600 purchases, so blended CAC is about ₹230.
Suppose 25% of those purchases were returning customers. That share is an assumption for illustration. Yours will differ.
| Blended | New customer | |
|---|---|---|
| Purchases counted | ~2,600 | ~1,950 |
| CAC | ~₹230 | ~₹305 |
Same spend, same orders, a CAC about a third higher. If you set targets or calculate payback off the ₹230, you are too optimistic about growth.
Where existing customers sneak in
| Source | Why |
|---|---|
| Retargeting and dynamic product ads | Reach past visitors, and buyers unless excluded. See the DPA death spiral |
| Broad prospecting with no purchaser exclusion | Broad targeting does not know your customers unless you tell it |
| Advantage+ sales campaigns | Can serve existing customers unless you set an existing customer budget cap |
| Lookalikes seeded from customer lists | Can include people who already bought |
For Advantage+ campaigns, define your existing customers in account settings. Then the audience type breakdown splits results into new and existing. Menu paths change, so check your account.
How to measure it
- Pull first-time vs returning orders from your store for the same dates as your ad data. In Shopify, use the new vs returning customer report.
- New customer CAC = ad spend / first-time customers.
- Compare it with blended CAC. The gap is how much existing customers flatter the platform number.
- Split by campaign type where you can.
- Fix the leaks: exclude purchasers from prospecting, cap the existing customer share, and keep retargeting to a sensible share of spend.
Your ad platform and your store will never match exactly because attribution and tracking differ. Use the comparison for direction and watch the trend.
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Request a Paid Media Profitability ReviewWhat to do with the number
If new customer CAC sits far above blended, repeat buyers and retargeting are propping up your dashboard. Set growth targets on new customer CAC. Then check that those customers pay back with CAC payback period.
Returns and discounts change that math, as shown in CAC vs LTV for fashion brands. Margin matters as much as cost, so see contribution margin vs ROAS. To test whether retargeting adds sales at all, see incrementality testing.
A five number monthly scorecard
| Metric | What it tells you |
|---|---|
| Account reach | How far delivery goes |
| Overlap rate | See account reach vs campaign reach |
| Account frequency | See account frequency |
| New customer share of purchases | Whether ads find new buyers |
| New customer CAC | Whether that costs too much |
If the first three look fine and the last two get worse, existing customers are taking more of your budget.
Common mistakes
| Mistake | Fix |
|---|---|
| Using platform cost per purchase as CAC | Use first-time customers only |
| Store data for a different window | Match spend and order dates |
| Purchaser exclusion window too short | Match it to your repeat cycle |
| Cutting retargeting to zero | Keep it to a share that does not crowd out prospecting |
| Judging one month | Watch the trend |
FAQ
What is the difference between new customer CAC and blended CAC? Blended divides spend by all purchases. New customer CAC divides it by first-time buyers, so it reflects the true cost of adding a customer.
How do I find my new customer count? Use your store's new vs returning customer report for the same dates as your ad spend. In Shopify, look at first-time customer orders.
Why does Meta report more purchases than my store shows as new customers? Meta counts all attributed purchases, repeat ones included, and its attribution window differs from your store's.
Can Meta show me new vs existing customers? In Advantage+ sales campaigns, yes, through the audience type breakdown once you define your customers. For other campaign types, use store data.
How long should my purchaser exclusion window be? Match it to how often customers buy again. A short repeat cycle needs a longer exclusion relative to that cycle.
The takeaway
Pull first-time orders from your store, calculate new customer CAC monthly, and set growth targets against it instead of blended cost per purchase.
Want a second pair of eyes on your new customer numbers? Talk to us at growth@adtitudemedia.com.
Check this in your own numbers
We built a free calculator that shows how many months your customers take to pay back what you spent acquiring them, adjusted for RTO and repeat purchases. Run your numbers in the CAC payback calculator.