How to use the Biorhythm Cycle chart
- Enter your birth date. The reference date defaults to today, and you can change it to see the rhythm on another day.
- Check the physical (red), emotional (blue) and intellectual (green) curves on the chart. The dashed line is the reference date, and you can show 15, 30 or 45 days either side.
- Read the values for the reference date and the next peak, low and zero crossing in the tables, and save the chart as a PNG if you like.
How biorhythm is calculated
Biorhythm theory assumes a person rides three regular rhythms starting from birth. The physical rhythm has a 23-day period, the emotional one 28 days and the intellectual one 33 days. The day of birth is zero and each curve moves one step per day. The formula is simple: with t as the number of days since birth, physical is sin(2πt/23), emotional is sin(2πt/28) and intellectual is sin(2πt/33), and the result is multiplied by 100 to show a percentage. A curve near +100% is a peak, near −100% is a low, and the moment it crosses 0% is a zero crossing.
Because the three periods differ, the way the curves overlap keeps changing. The 23-day and 28-day rhythms line up again only after 644 days, and all three return to the start after 21,252 days (about 58 years). The tool draws the curves around the reference date and lists today's values, the rising or falling direction, the high, middle or low zone, and the dates of the next peak, low and zero crossing. Since a curve crosses zero every half period, which is not a whole number of days, zero crossing dates are shown as the nearest day.
All calculation happens inside the browser that opened this page. The birth date you enter is not sent to a server or saved, and the saved chart image does not contain it. Dates are calculated by whole days only and the time of birth is not considered.
Background and limits of the theory
The roots of biorhythm go back to Wilhelm Fliess, a Berlin physician in the late 19th century. Fliess believed he found 23-day and 28-day regularities in things like illness and birth, and in the 1920s an Austrian teacher named Alfred Teltscher is said to have added the 33-day intellectual cycle after noticing a pattern in his students' results. The theory spread widely among the public in the 1970s, but it never came from rigorous experiments.
The scientific verdict is sober. A comprehensive review published in 1998 examined 134 studies of biorhythm, found that 35 gave some support, and concluded that the theory is not valid overall. Controlled experiments comparing the cycles with academic performance have also reported no correlation. So the curves in this tool should never be taken as predictions of condition or luck.
It still has uses. You can enjoy seeing what a sine curve fitted to your own dates looks like, or compare today's values with family and friends as a light conversation piece. It can also serve as a classroom example of what three waves with different periods look like when overlaid.
On the other hand, do not leave important decisions such as health, exercise, driving, exams, contracts or investing to these curves. Do not cancel plans because a curve is low or push yourself because it is high. When you are worried about how you feel, look at your actual condition rather than the curve, and talk to a professional if needed.
Some books call the days when a curve crosses the zero line critical days, but no evidence for this has been found. This tool does not use that wording and only marks zero crossings. Please use it to look at the shape of the curves, not to raise anxiety.
Changing the reference date shows how far the curves move each day. The physical curve goes from peak to the zero line in about 6 days, the emotional in about 7 and the intellectual in about 8. This regular pattern is all the tool shows, while real daily mood and condition depend on far more factors such as sleep, meals and stress.
Tips for enjoying it
- Change the reference date and watch how the curves move.
- A 15-day range makes changes look larger, and 45 days shows the overall flow at a glance.
- Turn on a single curve with the checkboxes to compare shapes more easily.
- Save the chart as a PNG and compare it with friends for fun.
- Do not use the curves as a basis for health or important decisions.
FAQ
Is biorhythm scientifically valid?
No. A 1998 comprehensive review looked at 134 studies on biorhythm and concluded that the theory is not valid. This tool simply charts the formulas the theory uses for fun, and it does not predict your condition or luck.
Are there "critical days"?
This tool has no critical days. It only marks the points where a curve crosses the zero line as zero crossings. Some books call those days dangerous, but no evidence for that has been found, so do not worry or change plans because of them.
Can I look at the past or future?
Yes. Change the reference date to any day to see its values and the curves 15, 30 or 45 days either side. The reference date must be after the birth date, though.
Does the time of birth matter?
No. Only the number of days from the birth date to the reference date is used, so it is calculated by whole days. The time of birth and time zone are not considered.
Is my birth date sent to a server?
No. Everything is calculated inside this browser and nothing is saved or sent. The saved chart PNG does not include the birth date either.
Notes & limitations
This is a free calculator for fun. Biorhythm is an unproven theory, and the result cannot be a basis for any judgment about health, safety, studies, contracts or investing. The birth date you enter is not sent to a server and is calculated only in the browser. If you are worried about your physical or mental state, consult a professional.