Amazon believes its ads sell more than it has been taking credit for. Around a fifth of a brand's value on Amazon arrives after the attribution window has closed, according to the company's own estimates.

That attribution window typically runs seven to 30 days. Amazon reached its figure by studying more than 2 million campaigns that ran on its ad products in June. Now it is using the findings to help make the case for counting a full year of value.

"What we actually find is that roughly 20% of the sales value for a brand shows up over time and isn't captured in that immediate attribution window because that's just a cutoff date for measurement," said Lily Tong, a director of measurement at Amazon Ads. "It doesn't mean that you didn't create value."

Proving value over a full year is fast becoming table stakes, and Amazon, like Google, needs that proof more than most. Two forces are squeezing the search business that has anchored both companies' ad revenue. Better upper-funnel measurement and AI-driven shopping are pulling money out of search. At the same time, TikTok, Instagram, YouTube and creators claim credit for sales they had a hand in, even when the purchase happens on Amazon.

The stakes are clear. If a fifth of a brand's sales value materializes beyond the standard measurement cutoff, then current attribution models undercount Amazon's contribution by design. Amazon's push for a 365-day window would reframe how advertisers allocate budgets between search and upper-funnel channels — and how much credit rivals can claim for the same sale.