What is biorhythm theory?
Biorhythm theory is a popular idea that, from the day you're born, your physical (23-day cycle), emotional (28-day cycle), and intellectual (33-day cycle) condition rises and falls in a sine-wave pattern. Each rhythm moves between +100% (peak) and -100% (trough), and the point where it crosses zero is called a "critical day."
How is it calculated?
We calculate the number of days elapsed from your birth date to the date you want to check, then divide that by each rhythm's cycle length (23, 28, or 33 days) and plug it into a sine function to produce a value between -100% and +100%.
A note on accuracy
Biorhythm theory is classified as pseudoscience with no scientifically verified basis, and no academic study has established a real correlation with actual physical or mental condition. Please enjoy this as a fun reference only.
Frequently Asked Questions
What does a "critical day" mean?
A critical day is a day when a rhythm value crosses zero β believed (without scientific evidence) to be a turning point when that area (physical, emotional, or intellectual) becomes more unstable.
Can I compare multiple people's rhythms?
This calculator checks one person at a time. Try recalculating with a different birth date and jotting down the results to compare them yourself.