The evidence

Are biorhythms real?

The short answer

No.

Biorhythm theory has been tested many times, and the tests did not find that the cycles predict anything. Here is what was studied, what was found, and why we make a biorhythm app anyway.

The claim

What the theory claims

That three cycles of 23, 28 and 33 days begin at birth and run unchanged for life, and that where you are in each one affects your physical, emotional and intellectual state. If that were so, the cycles should show up in things that can be counted: accidents should cluster on critical days, athletes should perform better in high phases, students should score higher when the intellectual cycle is up.

Physical
23
Emotional
28
Intellectual
33

The record

What was tested

134

studies reviewed in 1998

  1. 01

    Accidents

    Industrial and traffic accidents, checked against the drivers' and workers' critical days, in several studies in the 1970s. The accidents fell on critical days no more often than chance would place them.

  2. 02

    Sport

    Sporting performance, including professional baseball and golf, checked against the players' cycles. No relationship was found.

  3. 03

    Exams

    Academic performance and examination results against the intellectual cycle, in studies of students in the 1970s and 1980s. No relationship was found.

  4. 04

    Mortality

    Deaths, including a 1979 analysis of the claim that people die more often on critical days. The dates were distributed by chance.

In 1998 Terence Hines, a psychologist at Pace University, reviewed 134 studies of biorhythm theory in the journal Psychological Reports. His conclusion was that the theory is not valid: the studies that reported an effect were the small and poorly controlled ones, and the larger, better-designed ones found nothing.

Human nature

Why it persists

Partly for the same reasons horoscopes do. A reading written in general terms is easy to fit to any day after the fact; the days it fits are remembered and the days it does not are forgotten; and a pattern that is personal, counted from your own birth date, feels like it ought to mean something. None of that is a failing in the people who enjoy it. It is how all of us read patterns.

Our position

Why we make a biorhythm app anyway

Because the value of a daily reading does not depend on the cycles being real. It depends on what you do with it. Reading where your cycles sit, and asking whether the day feels like that, is a small act of attention, and a reason to stop for a moment each morning. People who keep journals know that the writing is the point, not the prediction. BioCalendar is built to be used that way, and it says so inside the app.

BioCalendar never claims that a reading is accurate, that it predicts an outcome, or that it can tell you anything about your health, your money or your safety. If you ever see wording in the app or on this site that suggests otherwise, we want to know.

Editorial standard

How this affects what we write

Describe. Invite reflection. Never predict.

Every reading, every page on this site and every answer from the Companion is written to the same rule: describe where the cycles sit, invite reflection, and never predict. The editorial policy sets it out.

Evidence deserves a closer look.

Sources

Primary references behind this page.

  • Hines, T. M. (1998). Comprehensive review of biorhythm theory. Psychological Reports, 83, 19–64.
  • Khalil, T. M., & Kurucz, C. N. (1977). The influence of "biorhythm" on accident occurrence and performance. Ergonomics, 20, 389–398.
  • Wolcott, J. H., McMeekin, R. R., Burgin, R. E., & Yanowitch, R. E. (1977). Correlation of general aviation accidents with the biorhythm theory. Human Factors, 19, 283–293.
  • Louis, A. M. (1978). Should you buy biorhythms? Psychology Today, 11, 93–96.

Continue the story

Keep reading

  1. 01What is a biorhythm?A biorhythm is a cycle said to begin at birth and repeat on a fixed period: 23 days physical, 28 emotional, 33 intellectual. The theory and the evidence.
  2. 02A brief history of biorhythmBiorhythm theory from Fliess and Swoboda in the 1890s, through the 33-day cycle and the 1970s craze, to what the studies found when they tested it.
  3. 03About Biosoft GlobalBiosoft Global makes BioCalendar. It began with one person counting three cycles by hand in 1976, and has kept the records since. Who we are.