Marketing ROI & CAC by Channel
A blended customer acquisition cost is an average of things that have nothing in common. This calculator takes each channel separately, follows spend through leads and conversion to gross profit, and tells you which ones are paying for themselves.
Each row is a channel: what you spent, how many leads it produced, what share became customers, the average order and the margin on it. From that come three numbers the dashboards cannot give you. CAC is spend divided by customers. ROAS is revenue divided by spend, the figure the platforms report. Profit after CAC is gross profit minus spend — the only one that decides anything.
The spread is usually the surprise. In the sample data the blended CAC is 793, which describes no channel at all: email to the existing base brings customers at 173 and outdoor advertising at 4,235, twenty-four times apart. Three of the six channels return less gross profit than they consume, between them taking 364,000 of a 512,000 budget — and two of those three look respectable on ROAS alone.
That gap between ROAS and profit is the trap worth naming. A channel running at 3x ROAS on an 18% margin returns about 54 cents of gross profit for every unit spent, which is a loss dressed as a win. The marketplace row in the sample does exactly that: a healthy-looking 4.8x ROAS on thin margin, and still 23,856 in the red.
The second sheet sizes the prize without overstating it. Rather than applying the best channel's return to the whole reallocated budget — email works at that rate precisely because it is small and aimed at people who already know you — it uses the blended rate of every channel that already pays for itself. Moving the 364,000 at that rate swings the result by about 613,000, and the sheet says plainly to expect part of it rather than all of it, because channels get more expensive as you scale them.
