Private biorhythm calculator: your cycles stay on your device

20 June 2026 · 6 min read · By Tomasz Fiedoruk

A private biorhythm calculator stores your birth date and personal cycles where they belong: on your own device, out of reach of any server, advertiser or data broker. That is the design principle behind aimy.bio, built on the Sikora method of biorhythm tracking.

Why does privacy matter for a biorhythm app?

Your birth date is more than a calendar fact. Under the EU General Data Protection Regulation (GDPR), health-related data — including information that could be used to infer physical or emotional states — deserves heightened protection. A biorhythm app that tracks your energy, mood and focus cycles holds exactly this kind of data.

Most wellness apps treat that data as a product. They sync it to the cloud, use it to profile you for advertising, or sell anonymised datasets to third parties. Convenient for the app, problematic for you.

aimy.bio takes the opposite approach. Nothing you enter — your birth date, your daily diary ratings, your profile name — ever leaves your browser.

How aimy.bio keeps your data local

The technical mechanism is simple and auditable: localStorage, a browser standard that stores data directly on your device. There is no login, no account, no sync service, and no backend database waiting to be breached.

The only analytics aimy.bio uses is a self-hosted instance of Plausible — an open-source, cookieless tool that measures only anonymous aggregates like page visits and language. No personal identifier is involved, no cookie is set, and no third party receives the data.

The Sikora method and what it tracks

aimy.bio implements the discrete-phase biorhythm system developed by Dr. Jerzy Sikora. Unlike the traditional sine-wave chart, the Sikora method reads each biological cycle — physical, emotional and intellectual — as a discrete phase state: high (+), low (−), transition (X) or a rest (0). This creates a practical daily snapshot rather than an abstract curve.

The method tracks three personal cycles based solely on your birth date and, optionally, your birth time. That data is used locally for calculation and nowhere else. Learn more about the evidence behind biorhythms in do biorhythms work? or read about our open biorhythm study.

Is birth date really sensitive data?

Yes, and increasingly so. On its own, a birth date seems harmless. Combined with other data points — name, email, device fingerprint, location — it becomes a powerful identifier. Data brokers routinely use birth dates as anchor fields for building profiles.

Beyond identification, a birth date in a biorhythm or wellness app implies something about your health-adjacent habits: that you track your energy patterns, that you notice mood fluctuations, that you care about self-monitoring. That inference itself has commercial value to advertisers and, in some contexts, insurance relevance.

GDPR treats health-related inferences as special category data requiring explicit consent and strict handling. The simplest way to comply is not to collect the data at all. That is what aimy.bio does.

What happens when you add a profile?

When you create a profile in aimy.bio, the following happens:

• Your name and birth date are saved to the browser's localStorage key aimybio.v2.
• Your daily diary entries (energy, mood, focus ratings) go into aimybio.diary.
• Your preferences and app state go into aimybio.prefs.
• Nothing is transmitted to any external service.

You can inspect this yourself. Open your browser's developer tools, go to Application > Local Storage, and you will find all your data there — readable, yours, and deletable at any time by clearing the site data.

Is there any exception?

One. aimy.bio runs an optional anonymous research study — Phase 2 — designed to test whether the Sikora method genuinely tracks how people feel. Participation is entirely opt-in and requires a deliberate choice inside the app.

Even if you opt in, the design ensures your personal data never leaves your device. Your device computes a statistical correlation from your own diary entries. Only the resulting anonymous summary — a few numerical coefficients and a day count — is shared. Your birth date, your diary, and any identifier are never included. The study is designed to fall outside GDPR scope precisely because no personal data is transferred.

You can read the full study design in the open biorhythm study article.

Why most wellness apps work differently

The business model of free apps typically depends on data. An app that tracks your daily mood, sleep, or energy cycles has something valuable: longitudinal health-adjacent data at individual level. That data can be:

• Monetised directly through targeted advertising based on inferred health states.
• Packaged and sold to data aggregators or research firms.
• Used to improve AI models trained on health and behaviour data.

None of this requires your explicit knowledge or consent under many jurisdictions outside the EU. Even within the EU, consent mechanisms are often designed to nudge users toward agreeing.

aimy.bio has no advertising revenue and no data sale. The project exists as a tribute to Dr. Sikora's work and as a privacy-first wellness tool. The absence of a business model dependent on data is not an accident; it is the point.

How to verify aimy.bio's privacy claims

Healthy scepticism is the right attitude. You do not need to take our word for it. Several verification paths are available:

• Inspect network traffic. Open browser developer tools, go to the Network tab, and use the app. You will see no requests to external analytics services, advertising networks, or data collection endpoints beyond the self-hosted Plausible count.
• Read the source. The app runs as plain HTML and JavaScript with no obfuscation. The app.js and engine.js files are readable in the browser's source view.
• Check localStorage. As described above, all your data sits visibly in the browser's local storage — nowhere else.

Taking care of yourself starts with taking care of your data

The most consistent predictor of whether a wellness habit sticks is trust. If you suspect an app is selling your data or nudging your behaviour for commercial reasons, you are right to be guarded — and guardedness is the enemy of honest self-reflection.

aimy.bio is designed so that you can relax that guard. Your birth date, your mood ratings, your energy diary — they belong to you. The Sikora method is here as a reflective tool, not a data collection mechanism.

Open aimy.bio, add your profile, and start tracking your cycles with the confidence that your personal information stays exactly where you put it: on your own device.

Check your biorhythms

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