Compare purchase CPA with first-order margin
By Drizzle team
1 min read
A campaign can hit its target CPA and still leave too little contribution after product costs.
Calculate available room
Take net order revenue and subtract product, fulfillment, fees, and expected return costs. This is the amount available before ads and overhead.
Compare on the same basis
Use the CPA for the same customer or order definition. Separate first-time buyers from all purchases when retention matters.
Act on the gap
If CPA exceeds the available room, investigate offer, conversion, costs, or genuine repeat value. Do not relabel a loss as growth without evidence.
A worked example
A shirt brings $55 net revenue and incurs $22 in product, shipping, and payment costs. The $33 remaining before ads is the first-order ad room before overhead. If purchase CPA is $28, only $5 remains per order. A high ROAS headline may distract from that narrow contribution; a lower CPA or better margin may matter more than another impressive video.
Decision check
Keep the numerator, denominator, date range, currency, and attribution definition with every reported result. A metric describes one part of the shopper path; compare it with visits, purchases, and order contribution before changing the creative or budget. State what the observation cannot establish.