When I was pregnant in the early 2010s, the accuracy of due dates was way too controversial. So I launched a survey, ran it for a decade, and maintained charts of all the results.
After a good 13,000 entries or so I figured I had enough so I could archive what I'd learned, stop running the live survey, and host it on all on a site I would not have to pay for.
So if you are pregnant and wondering about your due date odds, congratulations! Go to https://spregnancy.blogspot.com/search/label/due%20date%20statistics to see what we learned together..