A biorhythm (from Greek βίος - bios, "life" and ῥυθμός - rhuthmos, "any regular recurring motion, rhythm") is an attempt to predict various aspects of a person's life through simple mathematical cycles. Most scientists believe that the idea has no more predictive power than chance and consider the concept an example of pseudoscience.
How to calculate Biorhythm
The equations for the cycles are:
Physical: sin(2π t/23)
Emotional: sin(2π t/28)
Intellectual: sin(2π t/33)
Where t indicates the number of days since birth.
Basic arithmetic shows that the simpler 23- and 28-day cycles repeats every 644 days (or 1-3/4 years), while the triple 23-, 28-, and 33-day cycles repeats every 21,252 days (or 58.2+ years).