Biorhythm theory: where it came from and what testing showed

1 September 2026 · 9 min read · By Tomasz Fiedoruk

Biorhythm theory holds that three cycles begin on the day you are born and then run unchanged for the rest of your life: 23 days physical, 28 days emotional, 33 days intellectual. Fixed lengths, no exceptions, and no influence from sleep, stress, illness or season. That rigidity made the theory unusually easy to check, and it has been checked, thoroughly.

In December 1980 the United States Patent Office granted Raymond Merritt patent 4,240,153 for a "biorhythm display device": a lit box holding three translucent belts, cut in the ratio 23:28:33 and turned by a small motor at one forty-eighth of a revolution per hour. Red for the physical cycle, green for emotional, blue for intellectual. The background section of the patent filing opens like this: "In recent years it has become increasingly well known in the scientific community that human beings periodically experience various cyclical physiological changes."

It was not well known in the scientific community. It had never been established there at all.

The distance between how settled the idea sounded and how little stood behind it is the real story of biorhythms, and a better one than either the believers or the debunkers usually tell. aimy.bio is built on one branch of this tradition, so we have every incentive to soften the verdict. We would rather write it down accurately.

What biorhythm theory actually claims

Three cycles, counted in days from your date of birth, each repeating at its own fixed length for as long as you live.

The strong form of the claim is where the trouble starts. These cycles are supposed to be universal, so everybody has them; deterministic, so your date of birth fixes them permanently; and sealed off from everything else, so no amount of shift work, illness, travel or age moves them by a day. A 2026 review in Chronobiology International describes the model in those exact terms, and adds the obvious problem: after a century of the idea circulating, no physiological mechanism has ever been identified that could produce cycles like these.

Rigidity is also the theory's one real virtue. Vague ideas cannot be wrong, and most of the wellness shelf is carefully vague. Biorhythm theory names three numbers and a start date, which means it produces predictions you can write down in advance, seal in an envelope and compare against what actually happened.

Fliess, Swoboda, Teltscher: where the numbers came from

Wilhelm Fliess was an ear, nose and throat surgeon in Berlin, and for roughly fifteen years he was Sigmund Freud's closest correspondent and sounding board. Britannica records the friendship as one that shaped early psychoanalysis. Fliess also believed that human life ran on two arithmetic periods, 23 days and 28 days, and Freud took the numerology seriously enough, by several accounts, to expect to die at 51 — twenty-three plus twenty-eight.

Hermann Swoboda, a psychologist in Vienna, reported periods of the same two lengths a few years later. His book Die Perioden des menschlichen Organismus in ihrer psychologischen und biologischen Bedeutung was published in Leipzig and Vienna in 1904, and the scan is freely readable today. Anyone curious about what the foundation of an idea looks like, before a century of retelling smooths it over, can spend a minute with it.

The third cycle arrived last and travels lightest. Alfred Teltscher, working in Innsbruck in the 1920s, is credited with the 33-day intellectual period, derived from watching the good and bad days of students. Fliess and Swoboda left books you can still open; for Teltscher's original work there is no comparably accessible text, and the cycle with the thinnest documentation is the one later writers repeat with the most confidence.

How a fringe idea became a consumer product

By the 1970s the idea had escaped into daily life. Newspapers ran daily biorhythm columns, transport companies reportedly scheduled around drivers' critical days, and the three waves turned up in shop windows as hardware.

The 1980 patent is a good core sample of that moment. Its prior-art section cites four earlier American patents for machines that plot the same three curves, a hand-held biorhythm calculator sold by Casio, and George S. Thommen's book Is This Your Day. Read the file and you are reading the paperwork of a small industry.

What stands out now is the tone. The patent does not argue for biorhythms; it assumes them — the way a thermostat patent assumes temperature. Somewhere between Vienna in 1904 and a lit box on an American desk in 1980, an unverified proposal quietly became a background fact.

What happened when it was tested

The testing had already begun.

In 1977, John Wolcott and three colleagues compared the biorhythm charts of pilots involved in general aviation accidents against what the model predicted. Their paper in *Human Factors* reported no correlation between accidents and the days the model flags as dangerous. Similar tests followed on industrial accidents, hospital admissions, exam grades, reaction times and sporting results.

The definitive account is Terence Hines's 1998 review in Psychological Reports, which gathered 134 studies, published and unpublished. Thirty-five of them reported some support for biorhythm theory. Hines worked through those thirty-five and found methodological and statistical errors big enough to explain the results. The other ninety-nine, covering a wide spread of outcomes, showed nothing at all. His conclusion ran to one line — biorhythm theory is not valid.

Those thirty-five are what a null effect looks like after it passes through ordinary human hands. Define a "critical day" a little generously, decide which comparison to run once you have seen the data, publish the analysis that worked, and a perfectly random world will hand you results. A claim can survive twenty years of testing that way, generating just enough near-misses to keep the question feeling open.

Why did the theory survive being disproved?

Because a chart that is wrong on average can still be right on a Tuesday.

You have a difficult morning, you check, and the emotional cycle is low. That lands. The dozens of days when the chart said low and the morning went fine leave no trace, because there was nothing to notice. We keep the hits and quietly drop the misses, and the pattern that results feels like evidence from the inside. That is confirmation bias, and nobody is exempt.

There is a second reason — and it deserves more respect than sceptics usually give it. The habit is genuinely useful even when the theory behind it is empty. A biorhythm chart is a dated, repeating prompt to stop and ask how your energy, mood and focus actually are today. Open-ended intentions to "check in with myself more" tend to evaporate; a specific ritual attached to a calendar tends to stick.

The word itself does the model a favour. "Biorhythm" sounds like the language of real chronobiology, where genuine biological rhythms are established, mechanistically understood and studied seriously. The 2026 Chronobiology International review makes the point that the term still turns up in scientific papers as a loose synonym for those real rhythms, which quietly lends the model a credibility it never earned. The two get pulled apart properly in biorhythms and circadian rhythm.

Where Sikora's reading fits

The idea had a later and quieter chapter in Poland. Dr Jerzy Sikora, writing in the 1980s, set out a version that reads each cycle as one of four discrete states rather than a point on a sine curve, and applied a birth-time correction that ordinary calculators drop. His 1983 book Biodiagram prawdę Ci powie is the source aimy.bio rebuilt the engine from, line by line.

Sikora changed the notation, not the evidence. Nothing in the record above stops applying because a cycle is written as a state instead of a percentage, and we do not claim the discrete reading succeeds where the sine model failed. What it deserves is an accurate description, which is harder to find than it should be. If you want the method itself, the phase tables and the birth-time correction, read the Sikora method explained; for the evidence question head-on, see do biorhythms work.

If it is not proven, what is left?

One thing, and it is not a small thing: your own data.

The theory makes dated predictions, so you can put it to a fair test on yourself. There is only one rule that matters, and it is the rule that separates a test from a story. Rate the day before you look at the chart. Once you have seen the forecast you cannot unsee it, and every rating afterwards is scored by someone who already knows the answer.

Treat biorhythms reflectively. They are a wellness lens and a prompt for self-awareness, not a forecast, a diagnosis or medical advice. For anything to do with your health, talk to a professional.

The blind diary in aimy.bio works that way. You log energy, mood and focus each day without the chart in view, your device works out the correlation locally, and nothing about you leaves your browser. People are using it: the diary went from 7 entries to 97, and then to 132, across three months — a small number of people who would rather find out. We are also running an open study of the method, pre-registered, with a commitment to publish the result even when it is null.

Raymond Merritt's machine turned its three belts at one forty-eighth of a revolution per hour, patiently, whether or not anyone was in the room and whether or not the person in front of it felt a single thing the colours promised. The belts were the wrong part of the design. The man standing there, paying attention to his own week, was the part worth keeping.

Want to see the three cycles for your own birth date, with the critical and zero days marked, and start a blind diary of your own? It takes a date, and everything stays in your browser: check your biorhythms.

← All articles