Blended CAC counts every dollar spent on sales and marketing against every new customer, whatever brought them in. Paid CAC only counts paid channels. Enter both and see the gap between them.
Blended CAC calculator
Whole business (period)
Paid channels only
Say a store spends $31,000 on paid ads and gets 340 customers from them — a $91 paid CAC. It also picks up 260 more customers from organic search, referrals and word of mouth at no direct ad cost, for 600 total. Blended CAC — total spend over total customers — comes out to $70, noticeably lower. Run LTV:CAC math against the $91 figure and you'd conclude paid is worse than it is; run it against blended and the picture is more accurate, because organic customers count toward the "acquisition cost" ledger too, even at $0 direct spend each.
Neither number is wrong on its own — they're just answering different questions. Paid CAC tells you what one channel costs to run. Blended CAC tells you what it actually costs, on average, to bring on a customer given everything running at once — the number that belongs in payback period and LTV:CAC math, since those are whole-business metrics.
The gap between the two is worth tracking on its own. It's roughly the size of your organic/earned acquisition — the customers who didn't need a paid click to find you. A growing gap over time usually means word-of-mouth, repeat brand searches or organic content are doing more of the work, which is exactly the kind of activity that's easy to have a hunch about but hard to see directly. Mentionfront tracks the brand and product conversation across social platforms, which is at least where to look for what's behind that gap.