CPA (Cost Per Acquisition)
Definition
A performance metric measuring the average cost to generate one desired conversion event — a trial sign-up, lead form, or purchase — through a Reddit Ads campaign. Calculated as total spend divided by total conversions.
Context
Reddit's September 2025 algorithm update improved CPA performance across most verticals by prioritizing engagement quality in delivery optimization. Reddit reported that ROAS across most verticals improved significantly post-update, suggesting the new quality signals better predict conversion intent than the prior engagement-volume signals.
Relevance to Reddit
CPA is the north-star efficiency metric for lower-funnel Reddit paid programs. Requires proper Pixel and CAPI setup to measure accurately. Establish a target CPA based on customer lifetime value before optimizing to this metric, and account for Reddit's tendency to undercount assisted conversions in last-click attribution models.
