How can I calculate CAC by cohort to see which acquisition channels create the fastest payback?
Quick Answer: Calculate CAC by cohort by grouping customers by acquisition date and channel, then dividing all acquisition costs attributable to that cohort by the number of customers acquired in the same cohort. To find the fastest payback, compare each cohort’s CAC against its cumulative gross margin or contribution margin over time, then identify the channel where the payback period reaches break-even fastest.
Detailed Explanation
CAC by cohort is the most accurate way to evaluate acquisition efficiency because it ties spend to the exact customers it produced, instead of blending performance across time or channels. Build cohorts by first-touch source, campaign, or channel and assign all attributable costs—media spend, sales labor, agency fees, creative, tooling, and landing-page production—into the same time window as the acquisitions. Then compute cohort CAC as total attributable acquisition cost divided by customers acquired, and layer in a revenue or gross-margin curve by month to determine when each cohort recovers its acquisition cost; the cohort with the shortest time-to-payback is your fastest channel. This method surfaces whether a channel with a higher upfront CAC actually delivers superior economics because of better retention, higher AOV, or faster conversion velocity.
Key Technical Drivers
- Create a cohort table with columns for acquisition month, channel, attributed spend, customers acquired, CAC, monthly gross margin, cumulative gross margin, and payback month; use the same attribution logic consistently across all rows.
- Attribute costs using a clear rule set: direct media spend goes to the source channel, while shared costs such as sales and operations should be allocated by qualified leads, opportunities, or closed-won revenue to avoid understating CAC.
- Compare channels on both CAC and time-to-payback: a channel with a higher CAC may still win if it generates higher gross margin per customer or shorter payback, so rank cohorts by cumulative margin crossing CAC, not spend alone.