Biorhythm
calculator
All it takes is your date of birth. You get three curves for body, feelings and mind, plus your next critical days. To be honest, science does not back the biorhythm. Treat it as a nudge to check in with yourself and leave predictions out of it.
Your birth date
When were you born?
From your birth date we work out the three curves for today. You can pick another day afterwards.
Contents
In three steps
Enter your date of birth
The biorhythm needs no time or place.
Look at the curves
Three values for today and the curve 15 days either side.
Check it against yourself
One sentence each evening shows after a few weeks whether the curves show you anything.
Video · 35 seconds
Your inner rhythm
The biorhythm describes three waves for your body, emotions and mind, all starting at birth. It's not backed by science, but it's a fascinating way to pay attention to yourself.
Read along
Your birthday started three rhythms inside you that are still running today. The idea is called biorhythm. It describes three waves within you. One for your body, in a 23-day rhythm. One for your emotions, in a 28-day cycle. And one for your mind, with a 33-day cycle. This is an invitation to pay attention to yourself. Check if you notice these phases. Calculate your three curves for free at theastroacademy.com.
What is a biorhythm?
The idea dates from around 1900. From the day you are born, three steady waves are supposed to run: one for the body over 23 days, one for emotion over 28 days and one for the mind over 33 days. Each wave climbs to a peak, drops below the middle line and returns. All the calculation needs is your date of birth. Time and place don't matter here.
When a wave sits above the middle line, that is a high phase. Below it, a low phase. The days when it crosses the line are called critical days, which the theory treats as switch days when you are meant to be less steady.
Important before you calculate: science does not support the biorhythm. In controlled studies, none of the curves tracked performance, mood or accidents. Treat it as a nudge to pay attention to yourself rather than a prediction, and never base decisions about health, work or driving on it.
The cycles at a glance
| Cycle | Length | Stands for, in the theory |
|---|---|---|
| Physical | 23 days | Strength, stamina, wanting to move |
| Emotional | 28 days | Mood, sensitivity, closeness |
| Intellectual | 33 days | Focus, memory, taking in new things |
| Intuitive (add-on) | 38 days | Gut feeling (added later, not in the classic model) |
23, 28 and 33 share no common factor, so the three curves only meet at zero together after 21,252 days, which is just over 58.2 years. In one lifetime your pattern hardly repeats.
Where the idea comes from
In the 1890s the Berlin physician Wilhelm Fliess described a 23-day and a 28-day rhythm. He was a close pen friend of Sigmund Freud at the time. Around then, the Viennese psychologist Hermann Swoboda landed on the same lengths. The 33-day cycle for the mind came in the 1920s from the Innsbruck engineer Alfred Teltscher, who tried to derive it from his students' results.
Biorhythms only caught on widely in the 1970s. Pocket calculators and later home computers made the arithmetic quick, magazines printed the curves, and shops sold dedicated biorhythm gadgets. The appeal has lasted. The math is simple, the picture looks good, and everyone gets a curve that is theirs alone right away.
What science says
The answer is clear: there is no solid evidence. In 1998 the psychologist Terence Hines reviewed well over a hundred biorhythm studies and found no effect beyond chance. Studies on accidents, sports results and exam grades came to the same conclusion. Real body rhythms do exist, such as the day-night rhythm or the menstrual cycle. They just aren't rigid, and they don't start on the day you are born.
So why does the biorhythm sometimes seem to fit? Hits stick in memory more than misses do. If you trip on a "critical day", you remember it, while the ten calm critical days before it fade. That is why this page asks questions instead of making claims. Check for yourself, keep notes and compare after a few weeks.
How to read the curves: an example
Take someone born on 15 March 1990 and look at 1 January 2026. By then 13,076 days have passed. Each curve works the same way: divide the days by the cycle length, and the remainder tells you where the wave is right now.
- Physical: 13,076 ÷ 23 leaves 12, so day 13 of 23. The curve sits at −14 % and is falling. It has only just crossed the middle line on the way down.
- Emotional: 13,076 ÷ 28 divides evenly (remainder 0). On this very day the curve begins a new round and sits at 0 %, which makes it a critical day.
- Intellectual: 13,076 ÷ 33 leaves 8, day 9 of 33. The curve sits at +100 %, almost at the top, and is starting to fall.
The average of the three curves is +29 % on this day. The next critical days after it: 9 January 2026, 12 January 2026. Worth asking yourself: do I notice anything on those days at all, or only when I checked the curve beforehand?
Three rules for reading it
- High or low is not a rating. A low phase only means the wave is below the line right now.
- Look at the direction, not just the number. +20 % and rising is a different moment from +20 % and falling.
- Check it against yourself. One sentence each evening over a few weeks tells you more than any curve.
If you are curious about rhythms you can actually measure in the sky: the Moon today shows the moon phase and moon calendar, and the moon phase calculator finds the phase you were born under. Also calculated from your date of birth alone: your life-path number in numerology. To read it yourself, try numerology in 5 minutes a day.
How often do you have a critical day?
On about 74 days a year, which is 20.4% of all days. Each curve crosses the middle line twice per round: physical every 11.5 days, emotional every 14, intellectual every 16.5 days. With 23 and 33 the crossing falls in the middle of a day, and that day counts as critical.
At least two curves on the same day happen on 320 of 21,252 days (1.5%). All three at once only 8 times: on the day of birth, and then not again for 19.7 years.
Because 23, 28 and 33 share no common factor, the whole pattern only repeats after 23 × 28 × 33 = 21,252 days, about 58.2 years. The numbers are the same for everyone, only shifted in time. Whether you notice anything on such days is something only you can check.
| Item | Value |
|---|---|
| Physical (23 days) | 1,848 days, 8.7% |
| Emotional (28 days) | 1,518 days, 7.1% |
| Intellectual (33 days) | 1,288 days, 6.1% |
| At least one critical cycle | 4,326 days, 20.4% |
| Critical days per year | about 74 |
| At least two on the same day | 320 days, 1.5% |
| All three on the same day | 8 times, at ages 0, 19.7, 21.5, 27.3, 29.1, 48.8, 50.6, 56.4 |
| Full repeat | 21,252 days (58.19 years) |
Counted day by day over one full repeat of 21,252 days from birth, with the same rule as the calculator above: a day is critical when a curve's zero crossing falls in it. The 38-day intuitive cycle is not included.
Biorhythm FAQ
- What is a biorhythm?
- The idea dates from around 1900. Three steady waves are said to start at birth: physical (23 days), emotional (28 days) and intellectual (33 days). The calculator shows you where each one stands on any given day.
- Is the biorhythm scientifically proven?
- No. Controlled studies found no link between the curves and performance, mood or accidents. A 1998 review covering well over a hundred studies came to the same result. Use it as a reason to check in with yourself, and never let it decide anything about your health or your driving.
- How is the biorhythm calculated?
- You count the days since birth and put them into a sine wave: value = sin(2π × days ÷ cycle length). That gives a number between −100 % and +100 %. The birthday itself is day 0, where every curve sits at zero.
- What is a critical day?
- It is the day a curve crosses the middle line, which the theory calls a switch day. Research found no effect, so you are the only one who can check whether those days feel different to you.
- What is the intuitive cycle?
- A 38-day cycle that some calculators added later. It is not part of the classic Fliess and Swoboda model. You can switch it on in the calculator.
- How does the partner biorhythm work?
- The gap between two birthdays never changes, so neither does the offset between two curves. That gives a fixed overlap per cycle in percent: 100 % means both curves rise and fall together. It is a reason for a conversation, not a verdict on a relationship. How much you are in step today is free; the fixed overlap per cycle comes with the whole app.
- What is free and what does the whole app add?
- Free and without sign-up: the three values for any day, the curve 15 days either side, your next critical days and how much you are in step with another person today. A free account adds the daily feeling journal, saved important days and the calendar subscription. The whole app adds the year in curves with a PDF, the week planner, every day in the day finder, six further cycles, Moon and planets, family and team, and the shift planner.
Read the numbers, not just work them out
Your life-path number comes from the same date of birth. 5 minutes a day is enough to understand it yourself.
Numerology in 5 minutes a dayFree, no sign-up.