Biorhythm theory postulates three primary cycles that alternate from the moment of birth: physical (23 days), emotional (28 days) and intellectual (33 days). The position of each cycle for the selected date is calculated, identifying critical days (zero crossing), high and low phases. A 30-day forecast is included with practical advice for each period — when to be active, when to rest, when to exercise caution.

Where it comes from

Biorhythm theory was proposed by Wilhelm Fliess, a Berlin physician and correspondent of Freud, around 1897. He claimed a twenty-three day male cycle and a twenty-eight day female cycle running from birth. Alfred Teltscher added a thirty-three day intellectual cycle in the 1920s. The idea spread widely in the 1970s when pocket calculators made the arithmetic easy. It should be said plainly: controlled studies have not found the predicted effects, and biorhythms are not accepted as science. They remain in use as a way of thinking about rhythm rather than as a measurement.

How the method works

The three cycles are calculated as sine waves starting at zero on the day of birth: physical at twenty-three days, emotional at twenty-eight, intellectual at thirty-three. A cycle above the line is read as a high phase, below it as a low one, and the day it crosses zero is called a critical day and read as unstable. Because the three periods are coprime, the full pattern repeats only after about fifty-eight and a half years.

What a reading covers

You get the three curves for a chosen period, the days each crosses zero, and the days when two or three are low or critical at once, which the theory treats as the ones to plan around.

Common questions

Is there evidence for this?: No. Reviews of controlled studies from the 1970s and 1980s found no effect on accidents, performance or mood beyond chance. It is worth using it as a prompt to pay attention, not as a forecast.
Is it the same as circadian rhythm?: No, and the difference matters. Circadian rhythm is a measured biological cycle of about twenty-four hours with a known mechanism. Biorhythms are fixed arithmetic cycles from a birth date with no mechanism proposed.
Are there more than three cycles?: Later authors added intuitive, aesthetic and spiritual cycles of thirty-eight, forty-three and fifty-three days. They have even less support than the original three.