Where the 70% Cart Abandonment Rate Comes From: The 50 Studies Behind the Most Cited E-commerce Statistic and How AI Search Answers Repeat It

"About 70% of online shopping carts are abandoned" is one of the most repeated numbers in e-commerce writing. Its usual source is the Baymard Institute's list of cart abandonment studies, which reports an unweighted average of 70.22% across 50 studies published from 2006 to 2025. We rebuilt that average from the list and examined what stands behind it. The 50 studies reproduce the figure exactly. Their median study year is 2013, 33 of the 50 are from 2015 or earlier, and 6 are from 2021 or later. Thirty studies (60%) come from companies that sell cart recovery or remarketing services; their mean is 72.78%, against 66.38% for the other 20. Three companies supply 44% of the studies. Reports of the same year disagree by up to 26.7 percentage points, which points to different definitions and client bases rather than to a common measurement. A least-squares trend rises by 0.65 points a year, from 64.9% in 2006 to 77.2% in 2025. Seven reasonable ways to aggregate the same list give values from 66.4% to 77.2%. On November 6, 2026, Google's AI Overviews for four cart abandonment queries all opened with 70.22% and then stated 29 further figures from 11 other sources, including mobile rates from 76.98% to 86% and food and beverage rates from 38.16% to 82% on the same day. We conclude that 70% is a stable convention built from vendor reports, not a measured rate for a defined population, and we suggest how writers, store owners and answer engines can cite it with its range, age and definition.