Short version: the calculator runs in your browser. You do not need an account, and this site does not ask for one.
Calculator inputs: none are sent to or stored by this site. Your numbers live in your browser and in the share link you choose to copy and send yourself — that link encodes your inputs in its URL, so do not share it if you do not want the recipient to see those numbers.
Amazon waitlist: only if you click Join and send the pre-filled email — that email goes to the site's mailbox, like any email you send. No address is stored by the waitlist form itself.
Standard hosting logs: the web host may log visits in the usual way (IP address, pages requested, browser type) for security and reliability. This site does not sell, rent, or trade personal data.
At launch, this site sets no analytics or advertising cookies of its own. If analytics or advertising are added later, this page will be updated first to say what they are and how to opt out. External links to Etsy, eBay, Shopify, and Amazon go to those platforms, whose own privacy policies apply once you leave this site.