Why blended and platform ROAS disagree, and how to report the gap

Know what each number counts

• Platform ROAS counts the revenue each platform attributes to its own ads, with its own window and model.
• Blended ROAS divides all revenue by all paid spend, using the store's own orders. It does not say which channel earned the sale.

List the usual causes of the gap

• Overlap: one order can be claimed by more than one platform, so platform totals can add up to more than the store's orders.
• Attribution windows: a platform's window may be longer or shorter than the window behind the blended figure.
• View-through: a conversion from someone who saw an ad but did not click may be counted by one source and not the other.
• Timing: an order on the last day of a period can fall into a different period in each source.
• Scope: if the numerator is total store revenue, blended ROAS includes orders that no paid ad touched.

Make the gap readable

• Show the platform figure, the blended figure and the difference in one table, for the same period and currency.
• Name the cause you can prove, and mark the rest as not explained. Do not round the gap away.

Decide which number to use

• Use blended ROAS for budget decisions across channels, and platform ROAS for tuning inside one channel. Say which one each decision used.
• If the gap widens for three weeks in a row, check tracking and windows before moving budget.

What to write in the client report

• Both numbers with their formulas, the gap in value and percent, the period covered, and the causes checked with their result.