To see which pages are useful, the site records for each page view and each outbound click: the time, the page, the referring website's domain, your browser's user-agent string, your country as reported by Cloudflare, and a hashed identifier derived from your IP address that changes every day. Your IP address itself is not stored.
When you use the calculator, the site records that the calculator was used on that page. The numbers you enter are not recorded; they stay in your browser's address bar so you can bookmark the result.
No cookies are set for visitors. No data is sold or shared. The site is hosted on Cloudflare.