Enter your date of birth (the time refines the calculation): the state of your three curves today, their slope, a short summary and the curves for the thirty days around today. If you filled in “My personal details”, the form is already complete. Everything is computed in your browser.
Enter your date of birth (and the time, if you know it) to see your three biorhythms for today.
Like the rest of this section, biorhythms are mostly used to answer a couple's question: compatibility. Two curves are laid over each other much as two birth charts are compared, to see where two people would be in phase and where they would not. It is a playful reading, not a validated method: the page explains the calculation, where it comes from and what the studies say.
Three sine-wave cycles are said to start at zero on the day of birth:
When a cycle is in its high phase, the corresponding ability is supposedly enhanced; in its low phase, diminished. Days when a curve crosses zero are called "critical days".
Unlike astrology, biorhythm theory has been tested extensively since the 1970s — precisely because it makes checkable predictions about accidents and performance. The verdict is unambiguous: no controlled study has found any relationship between cycles counted from a birth date and accidents, mood or achievement. Scientific consensus classes it as a pseudoscience.
Where such tools retain value for people who use them, it is as a prompt to stop and consider their physical form, mood and concentration — not as a forecast.
These compatibility readings — zodiac signs, Chinese signs, Vedic astrology, biorhythms, first names, life path — are gathered and calculated for two people on the Love compatibility page.
You don't have to believe an instrument predicts anything to get something out of it. Many people use biorhythms as a prompt to check in regularly on their energy, their mood and their concentration — three questions rarely asked otherwise. It is a logbook disguised as a graph.
The risk lies elsewhere: calling off an important decision because a “critical day” falls on it, or dismissing real fatigue because the physical curve is high. A symptom that persists is a matter for a doctor, not a chart.
By counting the days elapsed since birth and mapping that number onto each of the three cycles — twenty-three, twenty-eight and thirty-three days. Your position in the cycle gives a value between minus and plus one hundred per cent. The calculation is nothing mysterious: it is a simple sine function, which is precisely why it could be tested scientifically.
Because it is simple, numerical and personalised: three curves computed from a single piece of data, your date of birth. In the 1970s several transport companies used it to organise rosters, and dedicated calculators sold in large numbers. The apparent rigour of the arithmetic long stood in for evidence.
No, and the confusion is common. Circadian rhythms are real biological cycles of about twenty-four hours, driven by light and studied by chronobiology — an established scientific field that has earned a Nobel Prize. Biorhythms are supposedly fixed cycles counted from birth, and nothing corroborates them.
Links to official or reference sources. They open in a new tab.
The theory holds that three cycles begin at birth and run for life: a physical cycle of 23 days, an emotional cycle of 28 days and an intellectual cycle of 33 days. Compatibility between two people is then measured by how far their cycles are in phase: the closer the gap between the two dates of birth is to a whole number of cycles, the stronger the claimed agreement.
The calculator below applies that theory faithfully. It predicts nothing — the rest of the page explains why — but it is at least honest about what it does.
Enter two dates of birth to calculate how the cycles of two people line up.
Three reasons, in order of seriousness. First, the result never changes: the gap between two dates of birth is fixed, so your “compatibility” is the same at twenty and at seventy, in the first month and at the divorce. A quantity that does not vary cannot explain something that does.
Second, the cycles have no biological basis. Chronobiology knows plenty of real rhythms — the 24-hour circadian rhythm, hormonal cycles — but they differ between people, shift with light and sleep, and do not last a fixed number of days counted from birth. The 23, 28 and 33-day periods were asserted in the late nineteenth century by Wilhelm Fliess, without measurement.
Third, the theory has been tested. Dozens of studies looked for a link between cycle position and industrial accidents, road accidents, athletic performance or mortality. The fullest review, by Terence Hines in 2004, found no effect. This is not an open question; it is a closed one.
Because the word circulates, the calculation is entertaining, and it is better found here with the explanation than elsewhere without it. If you are looking for what actually predicts whether a couple lasts, the answer is not in dates of birth: it is in how two people talk to each other when they disagree.
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Text prepared with artificial intelligence, reviewed by the AffectionPlus team (method: About). Astrology: no study establishes what this page describes. Spotted an error? Write to us.
