Level: Advanced
The cost to acquire your next customer is rarely the same as your average cost so far, and understanding that difference is essential for smart scaling decisions.
Average CAC Can Mask a Rising Marginal Cost
A blended average CAC that still looks healthy can hide the fact that your most recent, incremental spend is acquiring customers at a much higher cost.
Calculate Marginal CAC From Recent Incremental Spend
Comparing the change in spend against the change in conversions over a recent period isolates what your next dollar is actually costing, rather than your historical average.
Use This Number, Not the Average, to Decide on Further Scaling
Continuing to scale based on an average CAC that no longer reflects current marginal reality risks scaling well past the point of genuine profitability.
Next step: Use the Sales Letter Writer to when marginal CAC starts climbing, treat stronger creative as one of your first levers to pull, since better copy can convert a larger share of that harder-to-reach incremental audience.