Privacy
Short version: the calculators run in your browser, and what you type into them never leaves your device.
What the calculators do with your data
Nothing leaves your browser. Every calculation on this site (pace, predictions, splits, VDOT, heart rate zones, the training plans) is JavaScript running locally on your device. There is no server-side computation, no API call and no database. Your race times, age and resting heart rate are not transmitted, not logged and not stored, not even in your browser between visits.
You can verify this: open your browser's developer tools, go to the network tab, and use any calculator. No request is made.
Server logs
The site is served from a web server that keeps standard access logs: the page requested, the time, your IP address, and your browser's user agent string. That is the ordinary minimum any web server records in order to function and to be debugged. These logs are not linked to anything you enter into a calculator, because that data never reaches the server in the first place.
Analytics
This site uses Google Analytics 4 to count visits and see which pages are useful. It is configured with IP anonymisation on and Google advertising signals off, so it is not used to build an advertising profile of you. Google Analytics sets cookies in your browser; you can block them with any standard content blocker or your browser's own settings without affecting any calculator on this site.
Advertising
This build carries no advertising. No ad network code is loaded and no ad-related cookies are set.
Affiliate links
Where a link to a retailer is an affiliate link, it is labelled as one at the point of the link. An affiliate link may earn a commission if you buy something, at no extra cost to you. No recommendation on this site is influenced by whether a link pays. The calculators and their methodology are the product, and a shoe recommendation that loses your trust is worth less than the commission.
Cookies this site sets
None. The site itself sets no cookies and uses no local storage. Any cookies present in your browser on these pages come from the third parties named above.
Children
This site is a set of general-purpose running calculators and is not directed at children under 13, and no personal information is knowingly collected from them.
Changes
This page describes the site as currently built and is regenerated with every deploy, so it reflects what is actually running rather than what was intended at some point in the past.