Calculate biorhythm

Plot the historical 23-, 28-, and 33-day biorhythm equations while making clear that the claimed predictions failed empirical review.

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ToolBiorhythm Calculator
Input
Output
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Preview

How it works

UTC days since birth become sin(2πd/23), sin(2πd/28), and sin(2πd/33), scaled from −100% to +100%. The sign of each matching cosine slope labels it rising or falling, while strict YYYY-MM-DD round trips avoid daylight-saving errors and impossible-date normalization.

Formula
cycle percentage = 100 × sin(2π × UTC days since birth ÷ period)
  • The three periods are reproduced from the historical theory rather than selected as biological defaults.
  • A review of 134 studies found errors in the 35 supportive reports and no support in the other 99, concluding that the theory is invalid.

Worked example

Birth date against a later date
Input
											Birth date: 1990-06-15
Target date: 2026-08-24
Output
												Days since birth: 13219
Physical percent: -99.8
Physical direction: falling
Emotional percent: 62.3
Emotional direction: rising
Intellectual percent: -45.8
Intellectual direction: falling

When to use this

Pseudoscience-history lessons reproduce the disputed curves, trigonometry classes plot three sine periods, and skeptical-thinking exercises compare birth-date charts with null athletic-performance findings.

Edge cases

  • 2000-02-30 is rejected before JavaScript can normalize it into a valid March date.
  • On the birth date, d equals zero, putting every sine curve at 0% with a positive rising slope.
  • A target before birth is refused because negative age lies outside the displayed historical model.

References