Because Shopify changed how it counts sessions between September 21 and 23, 2026. Your conversion rate is calculated on those sessions: if the session count moves, the rate moves, even with the same orders. Your sales aren't affected. The calculation rule is what changed. Your site did nothing wrong, or right. It just got a new referee.
The benchmark
Three rules changed, according to Shopify's help page on this update:
- a session no longer ends at midnight UTC. It closes after 30 minutes of inactivity;
- some sessions with no page view are now counted, for example someone who reaches checkout through a cart link;
- sessions from identified bots are removed from session reports by default.
The first rule had an effect that's rarely visible, but some teams know it well. In a meeting with a brand that also sells in the United States, the e-commerce manager explained that "all the sales made in the evening in the US show up the next day in reporting." The midnight UTC cutoff did the same thing to sessions: a visit that started at 7 p.m. in New York was split in two. That's no longer the case.
So the counter can go up or down. Here's a made-up example to show the mechanism: 1,000 orders on 60,000 sessions is 1.67%. Remove 6,000 bot sessions and you have 1,000 orders on 54,000 sessions, or 1.85%, without the site gaining anything.
The rule
Stop comparing a rate from before with a rate from after. Shopify says so itself: later data serves as the new baseline, and the history is neither deleted nor recalculated. To judge your business across the break, look at what didn't change definition: orders and revenue.
The steps
- The sessions report. Open it and find the step change between September 21 and 23.
- The new baseline. Set it over four full weeks after that date.
- The dashboards. Note the date in them, and review any target expressed as a conversion rate, including those tied to a bonus.
- Custom reports. Check them, along with any apps that read Shopify sessions.
- Leadership. Warn them before they ask:
"Our orders and revenue are comparable to last year. Our conversion rate no longer is, because Shopify changed the rule on September 21."
The trap
After the update, a rate that goes up or down tells you nothing about your site.
Another limit, less well known: the split between humans and bots only exists for sessions after October 7, 2025.
Your comparison with September 2025 can never be filtered the same way, and the product search and recommendation reports filter automatically, with no option to turn it off.
