Biorhythm Calculator

The three cycles this tool draws were never a single theory. The 23- and 28-day rhythms come from Wilhelm Fliess, a Berlin ear, nose and throat surgeon who published them in 1897 after tallying the days on which his patients fell ill. Hermann Swoboda, a psychology professor in Vienna, arrived at similar periods independently in 1904. The 33-day intellectual curve came later still — the 1920s — from Alfred Teltscher, an engineering professor at Innsbruck who believed he saw a rhythm in how readily his students absorbed new material. Three men, three cities, three decades, no collaboration; the familiar chart exists only because someone later stacked their numbers on one set of axes. And Fliess had an attentive reader — Freud wrote to him about periodicity from 1887 to 1904, and the surviving letters fill a Harvard volume.

Biorhythm theory imagines three fixed rhythms that start the day you're born and never reset. This tool simply draws them as three sine waves: a 23-day physical cycle, a 28-day emotional one, and a 33-day intellectual one. A "critical day" is just a curve crossing the zero line — pure geometry, not something your body feels. The physical curve, for example, crosses zero every 11.5 days like clockwork.

Because 23, 28, and 33 share no common divisor, the three curves only snap back to their exact birth alignment after their least common multiple: 23 × 28 × 33 = 21,252 days, about 58.2 years. Until roughly your 58th birthday you never repeat the same combined state twice. It's a pure number-theory quirk — coprime periods stretch the true cycle out to the product of all three.