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Biorhythm · Free chart

Free Biorhythm chart

Your biorhythm is three sine curves of 23, 28 and 33 days that all start on the day you were born, so your birth date is the only input: each curve's value is sin(2πt / T), with t the days you have lived. A critical day is a day on which a curve crosses its midline.

Enter your birth date to see the three cycles of biorhythm counted from it, of 23, 28 and 33 days, for today and the weeks around it, with each cycle's state and its next critical day.

A historical theory from around 1900, not a measure of the body.

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About Biorhythm

Your biorhythm chart is drawn from your birth date alone: born on 19 January 1989, you were on day 13,780 on 12 October 2026, and the chart shows where the three curves stood that day and rings the coming days when one crosses its midline, the theory's "critical days".

It follows a theory from around 1900 with several authors: two periods from the Berlin physician Wilhelm Fliess, their counting from birth from the Viennese psychologist Hermann Swoboda, the smooth curves from the American books of the 1960s.

How we compute it

sin(2πt / T), with t the whole days since birth and T = 23, 28 or 33; a critical day is the day of a midline crossing, as the calculators of the 1970s counted. Only the birth date is used.

An example

Sample person · born 19 January 1989

12 October 2026: day 13,780 of life

The physical, emotional and intellectual curves from 5 October to 4 November 2026, with 12 October marked; the states for that day are listed below the figure.
  • Physical, 23 days
  • Emotional, 28 days
  • Intellectual, 33 days
  • Critical day
Physical
High, rising, 73%
Day 4 of 23; next critical day 20 Oct
Emotional
High, rising, 78%
Day 5 of 28; next critical day 22 Oct
Intellectual
Low, falling, -46%
Day 20 of 33; next critical day 26 Oct
The three classical cycles of a fictional person born on 19 January 1989, drawn for 12 October 2026 (day 13,780 of their life) and the weeks around it. Each curve has its own line style and name; a ring on the midline marks a critical day. "Explore" opens the live chart, which counts to your own today and can add the later 38-day cycle. The tradition's reading of this period, not a prediction of events, and not advice on health, money, legal matters or relationships.

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