Privacy
Short version: there are no accounts, and what you type into a calculator never leaves your device.
Calculations stay in your browser
Every calculator runs entirely in the page. The expression you enter is never sent to a server, never logged and never stored.
What is stored locally
One setting: whether you chose the light or dark theme. It is kept in your own browser and is not readable by us.
Analytics
Google Analytics records which pages are viewed, roughly where in the world visitors are, and which site sent them. It does not receive what you type into a calculator — that never leaves your browser. It does set cookies, and if you are in the EU or UK you should be asked for consent before it loads.