Biorhythm Calculator

Biorhythm theory, popular in 1970s magazines, plots three sine waves from birth: physical (23 days), emotional (28 days), and intellectual (33 days). Each swings between +100 and −100 based on days alive mod cycle length — pure arithmetic, not measured heart rate or mood data.

On a target date the calculator reports where each wave sits as a percentage. High positive physical might be described anecdotally as "good for sports"; low intellectual as "bad for exams" — those narratives are folklore. Peer-reviewed medicine does not use biorhythms for diagnosis or training plans.

Defaults: birth January 15, 1990, target August 7, 2026 — thousands of days elapsed, so each cycle sits at a different phase. Change the target date to tomorrow or a vacation day to explore curves; the entertainment value is seeing how the three lines diverge, not forecasting outcomes.

Common mistakes include treating percentages as health guidance, comparing today's physical score to a fitness tracker, and sharing scores as if they were personality tests backed by research.

Plotting curves over a week requires running the target date day by day — this single-date view shows one snapshot, not a chart over time.

The 23-day physical cycle legend comes from Wilhelm Fliess in the 19th century — modern sleep and performance research does not validate the period lengths.

Apps that chart 30-day history use the same sine formula repeatedly — this page is one-day output aligned with that classic implementation.

Sharing a screenshot of today's percentages is common on social media — treat shares as entertainment, not health recommendations.

Combining biorhythm with moon phase or zodiac content is unrelated math — this tool does not blend other esoteric calendars.

Limits: entertainment formula only. Not medical, psychological, or athletic advice. For sleep, mood, or performance, use evidence-based tools and professionals.