Privacy

What we collect

Two things, and neither of them identifies you.

• Aggregated traffic statistics: which pages are viewed, from which country, on what kind of device, and which site you came from. They tell us what is worth writing.
• The technical data any site necessarily receives when you ask it for a page: IP address, browser type, date and time. These are handled by Cloudflare, which hosts and protects the site.

Calculator data stays in your browser

The durations, watts and weight you enter are saved in your browser’s local storage, under the key cpc:v2. The same key holds the snapshots you choose to keep with “Save this test” - date, CP and W′, the last four at most - and which of the two sources you picked, Strava or manual, so it is still there on your next visit. They are not sent anywhere: the site is static, there is no server to send them to.

They stay on your device until you clear the site data in your browser settings. You will not find them on another device, or in a private window: nothing is synchronised.

If you use the button that copies a link to your results, your tests end up in the link, after the hash. Browsers never send that part of the address to the server, so it reaches neither us nor Cloudflare, but anyone who receives the link can read it: share it as carefully as you would share the numbers themselves.

If you connect Strava

The calculator can read your rides from Strava to find the efforts it needs to estimate CP and W′. It is your choice: if you never press that button, the site never contacts Strava and this section does not apply to you.

When you do, we send you to Strava to grant permission. We ask for two things, both read-only: your activities and your profile. We cannot change or post anything on your account, and you can revoke the permission at any time from your Strava settings.

From the profile we read a single field, your weight, which fills in that box of the calculator on its own and gives you the per-kilogram values. Strava has no narrower permission, though: what you grant covers the whole profile, including the parts you set private. We would rather tell you than let you find out on Strava’s own screen. If there is no weight there, or you prefer a different number, the box stays yours: what you type by hand wins.

Your watts and your weight go from Strava straight to your browser and stop there: no data from your rides or your profile passes through any server of ours, and we keep no copy. The only thing that touches a server of ours is exchanging the authorisation code with Strava, because it needs a key that cannot live in a web page; that exchange carries no training data.

Your ride data and the rest of the profile are not saved: they live in the page’s memory and are gone when you close or reload it. All that stays in your browser’s local storage are the durations, watts and weight that end up in the calculator, exactly as if you had typed them yourself.

The access permission does stay, in your browser’s session storage under the key cpc:strava-session, so that reloading the page does not force you to connect again. Session storage dies with the tab: close it and the permission is gone. We deliberately did not use local storage: there it would survive the tab, and on a shared computer whoever sits down next would find it. Either way it lasts six hours at most, as long as Strava grants, and there is no long-lived credential: we never asked for permission to renew it.

A one-off random number goes into that same session storage while you connect, under the key cpc:strava-nonce. It only serves to recognise on return that Strava’s answer belongs to the connection you started; it is deleted as soon as it is read and says nothing about you.

Strava privacy policy

Statistics: Cloudflare Web Analytics

To count visits the site uses Cloudflare Web Analytics. It sets no cookies, writes nothing to your browser and builds no fingerprint of your device to recognise you: visits are counted and reported in aggregate.

What no site can make disappear is your IP address: it travels with every request, so Cloudflare receives it, exactly as it does to serve you this page. The legal basis is the legitimate interest in having basic readership statistics, and it stops there: no profiling, no advertising, nothing sold on.

Cloudflare privacy policy

Cookies and banners

The site sets no cookies, for tracking or anything else, and loads no third-party resources: the fonts are hosted here, not on an external CDN. Only two requests leave for anyone else: the Cloudflare visit counter described above, and the one to Strava, which only happens if you connect your account yourself. That is why there is no banner asking you to accept something: we neither store nor read information on your device in order to track you.

What the site writes to your browser is the calculator’s local storage and, if you connect Strava, the access permission plus the one-off number, both in session storage: they make a tool you chose to use work, and go no further.

Your rights

The GDPR gives you the right to access your personal data, to have it corrected or erased, to restrict processing and to object. There is little here to exercise them on: we keep no register of visitors, and an aggregated statistic cannot be traced back to you.

Erasing the calculator data is already in your hands: clear the site data in your browser. For anything else, or to complain, the contact is below; you can also go to your national data protection authority.

Changes

If what the site collects changes, this page changes with it. The date at the bottom says when it was last updated.