Your body.
Your data.
Your device.
Track your cycle, symptoms, and predictions — all encrypted on your phone. No accounts. No servers. No tracking. Not even an app store.
free · works offline · installs in one tap
Private by design
Everything is encrypted on your phone with a passphrase only you know. We literally cannot read your data — there's no server to read it from.
Knows your body
Log flow, moods, symptoms, and discharge in seconds. Cykel learns your rhythm and predicts your next period and fertile window — and shows its math.
Works offline forever
Install once and it never needs the internet again. No updates pushed behind your back, no outages, no data leaving your device.
On your phone in three taps
Cykel installs straight from this page — like saving a website you love, but it becomes a real app.
- 1Open CykelTap the button — it opens right in your browser, instantly.
- 2Add to Home ScreenUse your browser's share menu to add Cykel to your home screen.
- 3Set a passphrasePick something only you know. That's your key — there's no account to make.
Built so you don't have to trust us
Your reproductive health data is some of the most sensitive data you have. Cykel is built so it never leaves your control — and so anyone can verify that claim.
Encrypted on-device
AES-256 encryption with a key derived from your passphrase. Nothing readable is ever written to disk.
Zero network calls
After install, Cykel makes no requests. No analytics, no telemetry, no “anonymous” data collection.
No account, no servers
There's nothing to sign up for and nowhere your data is stored but your own phone. Nothing to subpoena.
Open source
Every line is public. Don't take our word for it — read the code or have someone you trust check it.
good questions
what if i forget my passphrase?
then your data is gone — and we mean really gone. there's no “reset password,” because there's no server holding a copy and no backdoor. that's the whole point. pick something you'll remember, and you can export an encrypted backup any time.
is it actually free?
yes. free, open source, and funded by people who believe reproductive health data should stay private. no ads, no subscription, no “premium” paywall. if you want to chip in, there's a tip jar.
why isn't it in the app store?
app stores require accounts and hand back usage data — the opposite of what cykel is for. installing straight from the web means no store account, no review gatekeeping, and nobody in the middle. on iphone you add it from safari; on android it's one tap.
can you (or anyone) see my data?
no. it's encrypted on your device and there's no server it syncs to. we can't see it, we can't sell it, and we can't be forced to hand over what we never had.
Your cycle, finally private.
Open Cykelfree · open source · on-device