Biorhythm Chart — 23, 28 and 33 days
Plots the three classical sine curves from a birth date, marks the days each crosses zero, and states plainly what the theory is worth: it has been tested against accidents, exams and mortality and found to predict nothing.
Three sine waves of your age in days — 23, 28 and 33 — drawn exactly, above a paragraph that says the theory has been tested and predicts nothing. Both halves belong to the tool: the curves are exactly defined, so they are computed exactly, and a chart with no caption would be an implied claim.
This is entertainment, and unusually for this corner of the site it is entertainment with a settled scientific verdict: biorhythms do not predict anything. The curves are drawn correctly; that is all they are.
9,810 days old
On this day
Thirty-one days around it
Critical days
No curve crosses zero on this day.
All three return to zero together every 21,252 days — 23 × 28 × 33, about 58 years and two months. It is the one genuinely interesting number in the theory, and it is a fact about the periods rather than about people.
A cycle is "critical" on the day its curve crosses zero. Two of the three half-periods are 11.5 and 16.5 days, so the crossing usually falls inside a day rather than on its boundary.
What this is worth
Sources
- The three periods — 23, 28 and 33 days — are the standard ones: Fliess (1890s) for the first two, attributed to Alfred Teltscher in the 1920s for the third.
- On the evidence: Terence Hines, "Comprehensive review of biorhythm theory", Psychological Reports 83 (1998), 19–64.
- The arithmetic here is sin(2πd/p) over whole days counted in UTC, so a daylight-saving change cannot shift the count by a day.
How to use it
Enter a birth date and a day to read
The count is whole days in UTC, so a daylight-saving change cannot shift it. Day 0 is the day of birth, where all three curves are at zero.
Look at the crossings, not the peaks
The "critical days" of the theory are the days a curve crosses zero, every half period. Two of the three half-periods are 11.5 and 16.5 days, so a crossing usually falls inside a day rather than on its boundary, and the tool marks the day it lands in.
Common questions
Does any of this work?
No. Biorhythm theory has been tested against accident rates, athletic performance, examination results and mortality; Terence Hines’s review in Psychological Reports 83 (1998), 19–64, surveys that literature and finds no support at all. The curves are computed correctly and they are exactly a sine wave of your age.
Where do 23, 28 and 33 come from?
Wilhelm Fliess, a Berlin nose-and-throat doctor and Freud’s correspondent, proposed 23 and 28 in the 1890s after noticing he could write most whole numbers as 23a + 28b. The 33-day cycle was added in the 1920s. That is the entire pedigree.
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