Biorhythms: Definition, History & Calculation

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

From astrology to fortune tellers, people have been trying to predict their future for centuries. This lesson will explore one such technique (called biorhythms) and will describe its place as a pseudoscience, its history, and the formulas used to make the biorhythm graphs.

Biorhythm Defined

Do you ever read your horoscope? Or have you visited a fortune teller? While these things are fun, they aren't science. In fact, they've earned the name pseudoscience, or false science, because even though they seem to have some scientific undertones, they lack the objective, rigorous research and scrutiny required by sciences like physics, chemistry, and biology.

Another type of pseudoscience, called 'biorhythms', originated in the 19th century and became popular in the 60's, 70's and 80's. Biorhythms are based on the idea that a person's life is on a cycle, with peaks and troughs. Using mathematical formulas, people can calculate and graph their cycles, thus determining good days (peaks) and bad days (troughs).

Biorhythms can be broken down into three cycles: the physical, the emotional, and the intellectual. Today, some even go further and look at the spiritual, aesthetic, and intuitional cycles (although we will only focus on the main three).

The physical cycle follows a 23-day period and focuses on stamina, health, and strength. The emotional cycle follows a 28-day period and is related to creativity, emotions, and intuition. Finally, the intellectual cycle lasts 33 days and is associated with thinking, judgment, and concentration.


During the late 1800's a physician and close friend of Sigmund Freud named Wilhelm Fliess came to the conclusion that a person's life is made up of 23 and 28-day cycles. He assigned the 28-day cycle to women (due to the menstrual cycle) and the 23-day cycle to men.

And Fliess wasn't alone. In the early 1900's a professor named Hermann Swoboda claimed to have independently come up with biorhythm cycles. And then there was Alfred Teltscher, another professor, who believed that student success was related to 33-day cycles. More believers came on the scene, and in 1923 the first academic book was written by Nikolai Parna entitled Rhythm, Life and Creation.

By the 60's, 70's, and 80's biorhythms had gained more popularity. From books to biorhythm calculators, many people had prescribed to the idea. Articles about biorhythms are found in scientific journals, but most of the studies (99 of 134) indicate that biorhythms are not valid and they are no better at predictions than random chance.

Formulas and Calculation

Now that you are familiar with the history, let's check out how biorhythms are calculated. For starters, they are based on sine waves, which are oscillating curves.

A sine wave
Sine wave

We will focus on three formulas: the physical cycle, the emotional cycle, and the intellectual cycle. You will notice the only difference between the three is the number of days in the cycle: 23, 28, and 33.

For all of the formulas, t represents how many days you have been alive.

Biorhythm formulas

In order to determine t, you need to add the following:

  • Your age x 365
  • The number of leap days (from the time of your birth until now)
  • How many days have passed since your last birthday

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