ROAS vs POAS for Ecommerce, How to Measure Paid Search and Paid Social Profitability
ROAS Tells a Story Revenue Wants to Hear
Return on ad spend is simple. It is also blind to margin. A 5x ROAS on clearance inventory with negative unit economics is a celebration that finance will not join.
POAS Puts COGS Back in the Room
Profit on ad spend divides contribution profit by ad spend. Contribution profit is revenue minus variable costs like COGS, payment fees, expected returns, and variable fulfillment. Fixed costs can stay out of the numerator for media decisions unless your CFO wants them in.
When ROAS Still Helps
ROAS remains a useful speed metric for intraday bidding when POAS calculations lag by a day. Use ROAS intraday, reconcile to POAS weekly, and never bonus teams on ROAS alone if margin varies by SKU.
Promo and Shipping Traps
Site-wide coupons inflate ROAS while shrinking margin. Model net revenue after discounts in the value passed to platforms.
Free shipping thresholds shift profitability by basket. If your value rules cannot reflect basket mix, POAS will wobble. Sometimes the honest answer is to optimize to margin buckets, not single SKU value.
Implementation Checklist
- Feed or catalog joins margin band to SKU ID used in conversion payloads
- Returns window reflected with delayed offline adjustments
- Finance sign-off on what counts as variable versus fixed
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