A historical theory · Fliess and Swoboda, 1897 to 1906

Biorhythm

Name: Biorhythm reading
Brand: EsoTerrier
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three cycles from around 1900, and what the studies found

Three curves of 23, 28 and 33 days, started on the day you were born and drawn side by side, as the theory's authors set them out.

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Your biorhythm chart is drawn from your birth date alone: born on 19 January 1989, you were on day 13,780 on 12 October 2026, and the chart shows where the three curves stood that day and rings the coming days when one crosses its midline, the theory's "critical days".

It follows a theory from around 1900 with several authors: two periods from the Berlin physician Wilhelm Fliess, their counting from birth from the Viennese psychologist Hermann Swoboda, the smooth curves from the American books of the 1960s.

At a glance

What it is: A theory from around 1900 of fixed cycles counted from birth
The cycles: 23, 28 and 33 days; a 38-day cycle added in 1978
Proposed by: Wilhelm Fliess (1897); counted from birth by Hermann Swoboda (1904); the 33-day cycle credited to Teltscher, undocumented
Popular: From the American books of 1961 and 1964 to the craze of the 1970s
What you enter: Your birth date only; the time and place play no part
Our method: sin(2πt / T) from the birth day; a critical day is the day of a midline crossing

Sample person · born 19 January 1989

12 October 2026: day 13,780 of life

Physical, 23 days
Emotional, 28 days
Intellectual, 33 days
Critical day

Physical: High, rising, 73%; Day 4 of 23; next critical day 20 Oct
Emotional: High, rising, 78%; Day 5 of 28; next critical day 22 Oct
Intellectual: Low, falling, -46%; Day 20 of 33; next critical day 26 Oct

Figure 1. The three classical cycles of a fictional person born on 19 January 1989, drawn for 12 October 2026 (day 13,780 of their life) and the weeks around it. Each curve has its own line style and name; a ring on the midline marks a critical day. "Explore" opens the live chart, which counts to your own today and can add the later 38-day cycle. Method: sin(2πt / T), with t the whole days since birth and T = 23, 28 or 33; a critical day is the day containing a midline crossing (cycle day 1, and day 12, 15 or 17), as the calculators of the 1970s counted.

On this page

How it works
Origins and history
The four cycles
Variants and what we leave out
Myths and disputed claims
Stories and lore
Evidence and criticism
Terms
Sample reading
Sources

How it works

The theory needs one input, the date of birth. The time and the place of birth play no part, because the cycles are counted in whole days. Each cycle is a wave of fixed length that starts on the birth day and repeats for life: 23 days for the physical cycle, 28 for the emotional and 33 for the intellectual. In the theory the upper half of each wave is a stretch of more of that quality and the lower half a quieter stretch. The books of the 1960s and 1970s tied the physical cycle to energy and stamina, the emotional cycle to mood, warmth and sensitivity, and the intellectual cycle to curiosity, memory and focus. Those are the theory's descriptions; the studies are set out under Evidence and criticism.

The curve. We draw each cycle as sin(2πt / T), where t is the number of whole days since birth (the birth day is day 0) and T is the cycle's length in days. The value runs from +100% at the top of the wave to −100% at the bottom, and it is read at the start of each day. Fliess himself drew no such curve: he added and subtracted whole multiples of 23 and 28, and the smooth waves belong to the popular books of the 1960s and 1970s.

Critical days. A critical day is the day on which a curve crosses its midline. A curve crosses twice in every cycle, so the critical days are the first day of each cycle and its halfway day: day 12 of 23, day 15 of 28 and day 17 of 33, and day 20 of 38 for the later intuitive cycle. That is how the pocket calculators of the 1970s counted, and how our engine counts. The word is Swoboda's, from 1904, but his critical day was a different thing: the period day itself, once per cycle (see Variants). On our chart a critical day is only the point where the curve turns from one half to the other.

States. Every day that is not critical falls in one of four states, by the half of the wave it is in and the way the curve is moving: high and rising, high and falling, low and falling, or low and rising. The direction comes from the slope of the curve at the start of the day, so the same value reads differently on the way up and on the way down. Terence Hines listed the same five positions in 1979.

How often. With the three classical cycles, about one day in five is critical for at least one of them. Two cycles cross on the same day about five times a year, and all three about once every 7.3 years: eight times in 21,252 days.

When the pattern repeats. Because 23, 28 and 33 share no common factor, the three curves line up again as they were at birth only after 21,252 days, about 58.2 years. With the 38-day cycle added, the whole pattern repeats after 403,788 days, about 1,105 years.

Comparing two people. Biorhythm books also compared two people's curves. The comparison is simply how far apart their cycles run: 100% when a pair of cycles is in step, 0% when it is opposite. Both people's cycles have the same lengths, so the figure never changes over a lifetime. We show it as arithmetic.

What EsoTerrier shows. The chart draws the three classical cycles for any day you choose and lists the critical days ahead; the 38-day intuitive cycle can be switched on and is labelled as a 1978 addition. A date before birth, or more than 54,900 days after it (a little over 150 years), is refused. We checked the engine on 12 October 2026 against an independent implementation, five web calculators and three published examples (Rosetta Code, the GNU gcal manual and Casio's patent), and every day matched.

Origins and history

Biorhythm was not discovered at one stroke; it was assembled over seventy years, and each part has its own author and decade.

When	Who	What happened
1897	Wilhelm Fliess (1858 to 1928), an ear, nose and throat physician in Berlin and a close friend of Sigmund Freud	In a book on the nose and the female sex organs he proposes two constant periods, 28 days ("female") and 23 days ("male"), whose sums of multiples were meant to time the events of life. No curves, no 33-day period, no labels "physical" or "emotional".
1904	Hermann Swoboda (1873 to 1963), a psychologist in Vienna, not yet a university lecturer	Builds openly on Fliess, applies the periods to memory, dreams and moods, counts them from the birth date (Fliess did not) and calls the period day "the critical day".
1906	Fliess, Der Ablauf des Lebens	The full statement of his periods. The same year he publicly accuses Swoboda and Otto Weininger of taking his ideas.
1909	Swoboda	A slide rule for finding critical days.
1920s, as later told	"Alfred" or "Friedrich" Teltscher, said to be an engineering teacher in Innsbruck	Credited with a 33-day intellectual cycle found in students' exam results. No publication by him has been found.
1930s to 1950s	Hans Frueh in Zurich, Hans Schwing (a dissertation at the ETH, 1939), Reinhold Bochow in Berlin and others	Books on "Periodenlehre" and, by 1937, "Biorhythmik", and the first accident studies. Known to us from catalogue records; what they found is known only through later promotional books.
1961	Hans J. Wernli, translated with George S. Thommen as technical supervisor	Biorhythm, published by Crown in New York: the Swiss three-cycle theory's first American book.
1964	George S. Thommen	Is This Your Day? (revised 1973) carries the three cycles to a wide American public.
1970s	Casio and others	Pocket biorhythm calculators (Casio's Biolator, on sale by 1976), printed chart services and coin-operated machines: the height of the craze. Casio's patent (Japanese priority 1975, United States grant 1978) records how the devices counted.
1978	Mort Gale	Biorhythm Compatibility, a popular book of 1978, has a 38-day "intuitive" cycle: the earliest appearance of it we have found.
1978 to 1998	Bainbridge, Hines, Zimmerman and many others	The controlled tests and the reviews.
2026	EsoTerrier	Our engine and pages rebuilt, and the advice our earlier texts gave by the cycles withdrawn.

Title page in German: Die Beziehungen zwischen Nase und weiblichen Geschlechtsorganen, in ihrer biologischen Bedeutung dargestellt, von Dr. Wilhelm Fliess, Leipzig und Wien, Franz Deuticke, 1897, with the oval library stamp of the Royal College of Physicians of Edinburgh. — Figure 2. Wilhelm Fliess, *Die Beziehungen zwischen Nase und weiblichen Geschlechtsorganen* (The relations between the nose and the female sex organs), Leipzig and Vienna, 1897: the first book in which his 23-day and 28-day periods appear. No curve and no label "physical" or "emotional" is in it. 1897. Wellcome Collection, Public Domain Mark 1.0.

What Fliess counted were whole days and their multiples, set out as arithmetic; the one figure in his 1906 book is a stepped line, not a wave. Swoboda turned the periods into a psychology of the individual and gave them a starting point, the birth date. The third cycle has no author we can read. The smooth curves and the labels physical, emotional and intellectual arrived with the books of the 1960s, by which time the theory came as a ready-made daily chart.

White curves on a black ground: two pairs of wavy lines, one solid and one dashed in each pair, labelled A, O, C and B, recording the rise and fall of a man's breathing; below them the printed caption, Fig. 107, Tracés des mouvements respiratoires de l'homme. — Figure 3. A man's breathing, written as curves by a recording instrument: Étienne-Jules Marey, *La méthode graphique*, Paris, 1885, fig. 107. The physiologists of Fliess's day drew rhythms that a body actually produced. Biorhythm's curves are not recorded from anyone; they are counted from a date. 1885. Wellcome Collection, Public Domain Mark 1.0.

The four cycles

Each cycle has its own page: its length, who proposed it, where its critical days fall, how the theory's writers and its critics saw it, and the claims made about it. Three are the classical cycles; the fourth arrived in 1978.

The three classical cycles

A later addition

Cycle 4: Intuitive (38 days)

Variants and what we leave out

Calculators and books disagree on several points. We describe the variants so you can recognise them, and say what we do.

Swoboda's critical day. For Swoboda the critical day was the period day itself, once per cycle, and he advised against large undertakings on it, such as an examination or a big speech. Later books moved the critical day to the two midline crossings of a sine curve. We follow the later convention, which every modern tool uses.
Which day a crossing belongs to. When a crossing falls in the middle of a day, tools disagree on the day it belongs to; our 2026 survey found three conventions. We take the day containing the crossing, as the devices of the 1970s did.
The hour of birth. Some calculators count from the hour of birth. No primary source does: the theory as published counts whole days. We ignore the time.
More cycles. Beyond the 38-day intuitive cycle, later books and apps add 43-day "aesthetic", 48-day "awareness" and 53-day "spiritual" cycles. We found no source for them older than the craze of the 1970s, and we do not show them.
Combined curves. Some tools average the cycles into one "overall" curve or mark a "critical zone". No source of the theory does this, and our own old combined zone mostly marked days on which no cycle was critical. Left out.
Fixed thresholds. Our old engine called a day critical when a curve was within 0.10 of the midline. That missed the physical cycle's halfway crossing and marked the intellectual one twice. It was replaced by the crossing rule.
Colours. The red, blue, green and violet of popular charts are a convention of the charts, not part of the theory. Our chart tells the cycles apart by line style and name as well as colour, so that no colour carries a meaning.
Advice by the cycles. The books from Thommen onwards, most web calculators and our own pages before October 2026 told readers what to do or avoid on given days. All of it is left out.

Myths and disputed claims

What is said about biorhythm, who says it, and what the record shows. The label is ours.

The cycles govern bodily condition, accidents, illness or the quality of decisions, so people should rest, take care or plan their days by them.
false

Who says it: Popular biorhythm books from Thommen (1964) on, most web calculators, and our own pages before October 2026.

What the record shows: The controlled studies, which a 1998 review of 134 of them sums up, did not bear it out.
A Japanese railway, an American airline and other firms halved their accidents by scheduling staff with biorhythm charts.
unverified

Who says it: Gittelson's and later popular books, and many web pages.

What the record shows: No controlled data stand behind the figures: a 1978 thesis repeats them second-hand from a popular book, and a Toronto newspaper could not find the Japanese studies the promoters cited. That one Japanese railway used the charts is recorded in a practitioner report of 1969.
Alfred Teltscher, an engineering teacher at Innsbruck, found the 33-day cycle in the exam results of thousands of students in the 1920s.
unverified

Who says it: Thommen and the popular books after him; most web histories.

What the record shows: No publication by him has been found. Thommen wrote in 1973 that his own search found none, and the first name, the post and the number of students vary between accounts.
The 28-day cycle is the Moon's month.
false

Who says it: Web pages, and our own page before October 2026.

What the record shows: A month from new moon to new moon is about 29.5 days. Fliess started from the menstrual cycle; in 1906 he gave the Moon's month as 29.5306 days and rejected it for his periods.
Swoboda found the same periods independently of Fliess.
false

Who says it: Popular histories, and our own page before October 2026.

What the record shows: Swoboda's book of 1904 builds openly on Fliess's of 1897. A 2003 study of their quarrel finds the charge of plagiarism out of place but confirms the dependence.
The four cycles realign only after more than two thousand years, and all three classical cycles are critical together about once a year.
false

Who says it: Our old page writer's source file and some web pages.

What the record shows: The four cycles repeat together after 403,788 days, about 1,105 years. The three classical cycles realign after 21,252 days and are critical together eight times in that span: about once every 7.3 years.
The cycles start at the first breath, when the newborn's own rhythm separates from the mother's.
unverified

Who says it: Our old page writer's source file, citing a page that does not say it.

What the record shows: The theory counts from the date of birth. No source gives the cycles a physiological starting point.
Fliess drew the cycles as sine waves and named them physical and emotional.
false

Who says it: Most popular histories.

What the record shows: Fliess added whole multiples of 23 and 28 days and called the periods male and female; the one figure in his 1906 book is a stepped line. The curves and the labels are standard in the books of the 1960s and 1970s; who used them first has not been traced.

Stories and lore

These are told as the sources tell them.

Fliess and Freud. Fliess and Freud were close friends and correspondents in the 1890s. Fliess's periods belonged to a wider doctrine of his: that every person is bisexual for life, the 28-day period being the female side and the 23-day period the male, together with a "nasal reflex" theory that tied the nose to the rest of the body. The friendship ended in the years around the priority quarrel of 1906.

The craze. In the 1970s biorhythm was everywhere: Casio's Biolator sold for about $30, one New York chart service said it had sold 100,000 printouts in three years, and biorhythm machines stood in arcades and amusement halls. Sports, celebrity and airline anecdotes passed from book to book without a controlled source behind them.

The railway and the airline. Popular books say that a Japanese railway and an American airline cut their accidents by scheduling staff with the charts. That a Japanese railway tried the charts is recorded; the figures come second-hand from a popular book, and a Toronto newspaper that went looking for the Japanese studies could not find them.

The teacher nobody can find. The 33-day cycle is told as the discovery of an Innsbruck teacher called Teltscher, whose students' exam results are said to have shown it. His first name changes between "Alfred" and "Friedrich", Thommen wrote in 1973 that his own search abroad found no document, and a 1978 thesis says the study was believed destroyed in the war. One lead is open: an Austrian newspaper of 22 June 1930 that names him beside "Periodenlehre" has not yet been read.

Swoboda's lost papers. Thommen also wrote that Swoboda's own research was lost in 1945. His papers that survive are now in the Brenner-Archiv of the University of Innsbruck.

Evidence and criticism

The large review. In 1998 Terence Hines reviewed 134 studies of biorhythm, published and unpublished. The 35 that reported some support had errors of method or statistics that account for it; the other 99 found no support at all, and he concluded that the theory is not valid.

Accidents. In 1979 Hines summed up the accident studies, which covered more than 25,000 accidents. He also showed where the promoters' figure of "60 percent of accidents on critical days" comes from: critical days are about a fifth of all days, so with the day before and the day after counted in, about 60 percent of any random set of accidents falls near one by chance.

Sport, births and exams. In 1978 William Sims Bainbridge reported nine statistical studies: Arnold Palmer's 243 winning days, the wins of 31 women golfers and the first wins of 143 men, 95 no-hit baseball games, the deaths of 274 pitchers, 565 births, and the exam scores of two classes.

One firm's accidents. In a thesis of the same year, Richard Zimmerman examined 222 accidents at one Portland firm over a year against nine hypotheses.

Easy to test, and tested. Because the periods are fixed from birth, the theory makes definite predictions for any date, which is why it was tested so often.

Our own record. Until 12 October 2026 our engine texts and cycle pages gave advice by the cycles. They were rebuilt that day, and these pages replace the last of the old wording.

Terms

Biorhythm: The generic name of the theory, one word, used here descriptively. A few compound names containing the word are registered as trade marks for other goods and services; we use only the plain word.
Biorhythmik: The German coinage of the Swiss and German writers of the 1930s, in print by 1937.
Cycle: One of the theory's waves of fixed length, counted from the birth day: 23, 28 and 33 days for the classical three, 38 for the intuitive cycle.
Cycle day: Where a day falls within a cycle, counted from 1. The birth day is day 1 of every cycle.
Critical day: Swoboda's term (1904). In our use, and that of the 1970s calculators, the day containing a midline crossing: cycle day 1 and the halfway day (12, 15, 17 or 20). A neutral turning point of the curve, never a warning.
Double and triple critical days: Days on which two, or all three, classical cycles are critical: about five a year, and about once every 7.3 years.
The five states: High and rising, high and falling, low and falling, low and rising, and critical. We do not use other labels for the curve's positions.
Male and female periods: Fliess's names for the 23-day and 28-day series. He used no other labels for them.
Sensitivity: Another name for the 28-day cycle, used in Casio's patent and in a 1978 study of accidents.
Intuitive cycle: A 38-day cycle first found in Mort Gale's book of 1978, a later addition to the theory. Off by default on our chart and labelled as later.
Compatibility: In biorhythm books, how far apart two people's cycles run: 100% in step, 0% opposite. It never changes over a lifetime, and we do not read it as a judgement of a relationship.

Sample reading

Sample reading, AI-written for a fictional person.

Read the sample (1,254 words)

AI output can be wrong.

A Mind Waking in a Quiet House

Jason, on the reading date of 27 October 2026, your chart shows a sharp split: your intellectual cycle of 33 days has just crossed upward to 19% on day 2, while your physical cycle of 23 days sits at minus 98% on day 19 and your emotional cycle of 28 days is sinking at minus 90% on day 20. Biorhythm is a historical theory with no scientific support, and what follows is what that theory reads in the shape of your 13,795th day. It is a remarkable shape.

Two of the classical lines lie near the floor of their low halves. The third has just surfaced. In the theory's own terms, the mind is stepping into its bright half while the rest of the household is still dimmed. The theory associates the intellectual high with curiosity and alertness, and its low halves for the physical and emotional cycles with quieter stretches: a quieter stretch for the body, and a more inward stretch for feeling.

What the theory describes is not a mind running at full volume. At 19%, the intellectual line has barely cleared the midline. Picture the first lamp switched on in a dark kitchen: enough to read a label by, enough to notice that the room has a shape. You may find your attention snagging on a small question this week and refusing to let it go. You are reading an article and a single sentence sends you off to look something up. Twenty minutes later you have three tabs open and no memory of why you started. That restless, low-grade interest is the theory's picture of day 2.

The Feeling Line Going Under

The emotional cycle is the more telling placement right now, because it is moving in the opposite direction. It is falling, not rising, at minus 90% on day 20 of 28. Fliess first set out this 28-day period in 1897 as his "female" period, tying it to the menstrual cycle; it was Swoboda, in 1904, who carried it over into moods, memory, dreams and the ideas that arrive unbidden. (Many pages call it a lunar month. It isn't. A lunar month runs about 29.5 days, and Fliess himself rejected lunar time for his periods.)

The theory reads this deep, descending stretch as inward. Not sad, necessarily. Withdrawn. Less available to the room. Others may experience you as slightly elsewhere: present at the table, answering questions, but with some part of your attention turned away and listening to something they cannot hear. Swoboda's emphasis on dreams and unbidden ideas fits this placement closely. The material that rises at the bottom of the emotional curve, in the theory's telling, comes from below rather than from conversation.

Here is the first friction. The newly lit intellect wants to inspect. The descending feeling line wants to be left alone. You may catch yourself trying to think a mood into sense, naming it, sorting it, assigning it a cause, when the theory would say the mood is simply passing through its quiet water and does not need an explanation to finish its course.

Where the Climb and the Descent Cross

Your physical cycle sits at minus 98%, as deep as the curve goes, but it is rising, on day 19 of 23. This is the oldest part of the theory: Fliess's "male" period of 1897. He never drew the smooth wave or called it physical. He worked in sums of whole multiples of 23 and 28, and the sine curve and the popular label belong to the books of the 1960s and 1970s. In those books, the low half is the quieter stretch and the high half the stretch of stamina and drive.

What matters in your chart is direction. Physical is turning upward from its lowest point. Emotional is still heading down toward its lowest point. These two lines are passing each other in the dark, one ascending, one descending. The theory's picture here is of an inner tempo that does not agree with itself: an impulse toward motion beginning to stir, while the feeling life wants stillness and privacy.

This is the edge of the moment, and its trap. With your intellectual line freshly bright and your physical line starting to lift, you may mistake the stirring for the whole of you. You may fill the days with plans, reading, problems to solve, and leave the emotional line to sink unattended underneath. The theory's cost here is not catastrophe. It is a kind of self-absence. You can stay so occupied with the lit kitchen that you never notice what has drifted down into the cellar.

Your intuitive cycle of 38 days, at 16% and rising on day 2, has to be named with care. It is not one of the classical three. Its earliest known publication is Mort Gale's 1978 book, decades after the others, and it shares none of their history. In the later versions of the theory, it speaks to instinct and inner sense. Its near-perfect alignment with your intellectual line (both on day 2, both just above the midline) gives the later theory a neat picture: hunch and reasoning waking together. Take it as a later voice offering a second opinion, not as part of the original chorus.

The Weather of November

The theory marks its turning points as critical days: midline crossings, neutral, signifying change of phase and nothing more. Your next run of them falls close together:

The physical line crosses on 1 November and again on 12 and 24 November. The emotional line crosses on 5 November and again on 19 November. The intellectual line crosses on 11 November.

Read as the theory's weather, early November carries a particular texture. On 1 November, the physical line rises through the midline into its high half, so the stirring you may already feel becomes, in the theory's language, a stretch of energy. Four days later, on 5 November, the emotional line reaches its own crossing. The 28-day curve hits a critical day at cycle day 1, which means the descent you are in now finishes and a new cycle begins. Then on 11 November the intellectual line, which is only just beginning to rise now, completes its high half and turns down through the midline. The physical line turns again the next day.

So the arrangement you are living in today, mind up and feeling down, does not hold for long in the theory. Within two weeks, the order inverts. Feeling starts a new cycle, the mind goes into its quieter half. The present stretch is a brief window in which your intellectual line runs ahead of the others, and it closes on 11 November.

The popular books of the 1970s treated days like these as dangerous and told readers to be careful or reschedule. That claim was tested in well over a hundred controlled studies and found no effect beyond chance. Nothing in these dates asks you to arrange your life around them. They are a calendar of turning lines, nothing more.

One Thing to Try

Each evening between now and 11 November, write two lines. First line: what caught your mind that day, the question that wouldn't let go. Second line: what you felt that you did not mention to anyone. Don't analyse the second line. Just write it down and leave it. The theory pictures your intellect as awake and your feeling life as withdrawing, and the exercise lets both be seen without either taking over the other. When the lines invert in mid-November, read back over the page. You will have a record, in your own handwriting, of a fortnight in which one part of you was busy and another part was quietly speaking.