Example 1
- Birth: 1990-05-15
- Target: 2024-05-15
12419 d · P −27 · E −22.3 · I 86.6
Exactly 34 years later; intellect high, body and emotions slightly below zero.
Biorhythm calculator
From birth date to a chosen day you compute three sine waves: 23-day physical, 28-day emotional, 33-day intellectual. The result is a cycle phase, not a body measurement.
Here three sine cycles run from birth date to a chosen day. This tool is for entertainment and learning, not fortune-telling or life advice. It does not replace personal, medical or financial decisions. Also try the moon phase, zodiac sign and Chinese zodiac. Article: Biorhythms.
Result
Pick a birth date and a target date to see biorhythms.
How it works
Biorhythms in the classic model are three sine waves from the birth date: physical (23 days), emotional (28 days) and intellectual (33 days).
First we count whole days between birth and the target date (UTC). Then for each period we take sin(2π · days / period) and scale it to about −100…+100.
A positive value is often called a “high” phase, a negative one a “low” phase, and near-zero a transition. Those are popular metaphors, not physiological measurements.
Example: born 1990-05-15, target 2024-05-15 → 12419 days; physical ≈ −27, emotional ≈ −22.3, intellectual ≈ 86.6.
The model ignores birth time and place. It is also not the moon phase (different period and astronomy). Tropical and Chinese signs are separate date labels.
Biorhythm history is 20th-century and scientifically contested. Treat the output as a sine-and-period exercise, not a forecast of athletic form or mood. The target date cannot be earlier than birth. On equal dates the day count is 0 and all sines start at zero. The number sits in a 1-9 cycle.
Formula
days = target_date − birth_date (UTC whole days).
value = 100 · sin(2π · days / period), where period ∈ {23, 28, 33} for physical, emotional and intellectual cycles.
How to use the calculator
- Pick a birth date, YYYY-MM-DD.
- Pick the target date you want the waves for.
- Click Calculate. The result is the day count and three cycles: 23, 28, and 33 days.
- Check 15 May 1990 → 15 May 2024: 12419 days, intellect high, body and emotions a little below zero.
- These are sines from the date, not a horoscope. Moon phase lives on its own page.
Three sine waves from the birth date
From birth to a chosen day: 23, 28, and 33 days. The result is a cycle phase, not a body reading or a day forecast.
- cycle
- Physical 23, emotional 28, intellectual 33. Phase from the birth date to the chosen day. Not a body measurement.
- phase
- A position on the wave, not how you feel. The three periods are fixed. Not a health forecast.
Suggested uses
- Quickly compute the three classic sine waves for a date.
- Learn the 23 / 28 / 33 periods with concrete cases.
- Compare several target dates against the same birth date.
- Practice sine and modulo-period arithmetic.
- Pair with the moon phase (for fun, not as a “day diagnosis”).
- Check that a hand sine calculation matches the tool.
Examples
Example 2
- Birth: 2000-01-01
- Target: 2020-01-01
7305 d · P −63.1 · E −62.3 · I 75.6
20 years later; physical and emotional in a low phase.
Example 3
- Birth: 1985-11-22
- Target: 2024-01-01
13919 d · P 88.8 · E 62.3 · I −97.2
Body and emotions high, intellect near a minimum.
Example 4
- Birth: 1995-03-10
- Target: 2025-03-10
10958 d · P 39.8 · E 78.2 · I 37.2
30 years later; all three values positive.
Example 5
- Birth: 1977-07-07
- Target: 2024-07-07
17167 d · P 63.1 · E 62.3 · I 97.2
All cycles in the upper half; intellect near a maximum.
Example 6
- Birth: 1988-08-08
- Target: 2024-08-08
13149 d · P −94.2 · E −62.3 · I 28.2
Physical near a minimum, emotions negative, intellect slightly positive.
Example 7
- Birth: 1990-05-15
- Target: 2024-05-15
12419 d · P −27 · E −22.3 · I 86.6
Biorhythm calculator: 15 May 1990 to 15 May 2024.
Example 8
- Birth: 1990-05-15
- Target: 1988-08-08
-645 d · P -27 · E -22.3 · I 28.2
What waves from 15 May 1990 back to 8 August 1988? -645 d, P -27, E -22.3, I 28.2.
Related calculators
Frequently asked questions
What are biorhythms in this model?
Three sine waves with periods 23, 28 and 33 days counted from the birth date. It is a popular model, not a lab measurement.
How should I read positive and negative values?
In popular storytelling plus is a “high” phase, minus a “low” phase, and near zero a transition. That is metaphor, not diagnosis.
Does birth time matter?
No. We count whole days between calendar dates in UTC.
What if the target date is earlier?
The result is rejected. The target must be on or after the birth date.
How is Biorhythm calculator different from Moon phase?
Moon phase uses a ~29.53-day synodic period and disc astronomy. Biorhythms are three separate sines from birth.
Is this fortune-telling or health advice?
No. The calculator is entertainment and education. It does not replace medical, sports or life advice.
Why 23, 28 and 33?
That is the classic 20th-century biorhythm convention. Other periods are not part of this version.
What does day-in-cycle mean?
It is the position modulo the period (0…period−1). The sine turns that position into a wave “height”.
How many days and which waves from 1990-05-15 to 2024-05-15?
12419 days. Physical about -27, emotional about -22, intellectual about +87. Cycles 23, 28 and 33, not the Moon phase.
What if birth is blank and the target is 2024-05-15?
Error. Both dates are required. 1990-05-15 and 2024-05-15 are in example 1. A blank birth is not zero days.
Knowledge sources
The calculator reads a date or a tradition table. This is not fortune-telling, not an astrologer’s chart and not a diagnosis.
Page updated in 2026.