Biorhythm Calculator
Enter your birth date and a target date on the left; the three rhythm values update instantly on the right, with the 30-day curve below.
Input
Enter a birth date and the results update automatically.
Result
- Physical (23-day)
- —
- Emotional (28-day)
- —
- Intellectual (33-day)
- —
- Average of three (ref.)
- —
30 days around the target date
The dashed center line is the target date. Values near 0% are transition points; +100% is a peak, −100% a trough.
Biorhythm theory is not a scientifically validated prediction tool. Use it for fun and self-observation only; base health, safety, and important decisions on real information and professional advice.
ready to use.
- Visible firstKeep the input and result positions clear.
- Results firstPut the main number up front and keep the process secondary.
- Less to askNo sign-up or extra information before using the tool.
How to read the biorhythm curves — and the limits of the theory
Biorhythm theory assumes three sine waves start at birth: a 23-day physical, a 28-day emotional, and a 33-day intellectual cycle. This calculator applies that classic formula as-is: days since birth go into each cycle, producing values between −100% and +100%, drawn as a 30-day curve around your target date.
To be clear: biorhythms are not scientifically validated. Controlled studies of accident and performance data found no meaningful predictive power. Treat this page as entertainment and a starting point for self-observation.
The formula: three sine waves
Birth is day zero; days lived divided by each cycle sets the sine phase, shown as a percentage.
- rhythm = sin(2π × days ÷ cycle) × 100
- Physical 23 · Emotional 28 · Intellectual 33 days
- Values range from −100% to +100%
Screen flow: just two dates
Enter the birth and target dates and the results update without a button. The Today / Tomorrow / +7 chips switch the target date quickly for comparison.
Reading the curve: peaks, troughs, transitions
The dashed center line is the target date.
- Near +100%: a peak for that rhythm
- Near −100%: a trough
- Crossing the 0% line: a so-called critical day
- The three curves have different periods, so they peak on different days
Where 23, 28, and 33 come from
The cycles trace back to claims by Wilhelm Fliess and contemporaries around 1900. They resemble the numerology of that era rather than observed statistics, and are unrelated to modern chronobiology (circadian research).
Example: born 1995-03-15, target 2026-07-11
The default profile computes as follows.
- Days lived
- Day 11,441
- Physical (23)
- sine ≈ +39.8%
- Emotional (28)
- ≈ −62.3%
- Intellectual (33)
- ≈ −94.5%
Scientific tests have come up negative
Including a hospital study testing lunar phases and biorhythms against trauma admissions, controlled evaluations found no predictive power.
- No reproducible link between rhythm phases and accidents, surgery outcomes, or sports results
- Do not base health or safety decisions on these values
- Regular sleep and exercise beat any curve
If it has a use: a frame for self-observation
It is a decent excuse to start logging how you actually feel. After a few days of honest notes you will usually find that sleep, caffeine, and stress explain far more than the curves do.
Biorhythm FAQ
Is there scientific evidence for biorhythms?
No. Studies checking accident and performance data found no predictive power in the 23/28/33-day cycles. This calculator shows the classic formula as-is, for entertainment and self-observation.
What formula does it use?
With t as the days from birth to the target date, each rhythm is sin(2π×t÷cycle)×100, using 23 days (physical), 28 (emotional), and 33 (intellectual).
What does crossing 0% mean?
Days where a curve crosses the 0% line are called critical days — transition points in the theory. No correlation with real accidents or condition has been verified.
Are leap years and month ends handled correctly?
Yes. Dates are compared as calendar days at UTC midnight, so leap years (including Feb 29 birthdays) and month boundaries are exact.
What is the average of the three rhythms?
It is not part of the classic theory — just a convenience reference for seeing all three at once. Like the individual rhythms, do not use it for predictions.
Reviewed: 2026-07-11. This tool is for entertainment and self-observation, not for medical or safety decisions.