See where your three classic biorhythm cycles stand today or on any date: physical (23 days), emotional (28 days) and intellectual (33 days), with peaks, critical days and a day-by-day chart. Just for fun.
Last updated:
Enter your values to see the result.
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How to use the Biorhythm Calculator
Enter your date of birth.
Pick the date to check (today by default).
Choose the chart length and whether it starts on that date or a week earlier.
Read the cycle values: +100% is a peak, −100% a low and values near 0 mark critical days.
Scroll the chart and table to plan ahead, or download the table as CSV.
The biorhythm formula
Every cycle starts at zero on the day you were born and rises first. For a date that is t days after your birth, each value is
value = sin(2π × t ÷ period) × 100%
so a cycle reaches its peak (+100%) a quarter of the way through its period, returns to zero at the halfway point and hits its low (−100%) at three quarters. Because the periods differ, the three curves drift in and out of step, which is what makes each day's combination look different.
Cycle
Period
Peak on day
Zero crossings on days
Said to influence
Physical
23 days
5.75
0 and 11.5
Energy, stamina, coordination
Emotional
28 days
7
0 and 14
Mood, sensitivity, creativity
Intellectual
33 days
8.25
0 and 16.5
Memory, focus, reasoning
Intuitive (secondary)
38 days
9.5
0 and 19
Perception, hunches
Aesthetic (secondary)
43 days
10.75
0 and 21.5
Sense of beauty and harmony
Spiritual (secondary)
53 days
13.25
0 and 26.5
Inner calm, reflection
The emotional cycle is exactly four weeks long, so it always falls on the same weekday in the same phase: if you were born on a Tuesday, your emotional critical days are always Tuesdays.
Reading your chart
Above the line (0 to +100%): the "active" half of the cycle in biorhythm theory.
Below the line (0 to −100%): the "recharging" half.
Critical days: days when a curve crosses zero. Days when two or three cycles cross at once are the ones biorhythm fans watch most.
Rising or falling: whether the value is heading toward a peak or toward a low.
Biorhythms were popularised by Wilhelm Fliess and Hermann Swoboda around 1900 and became a fad in the 1970s. Scientific studies have not found that they predict anything, so enjoy the chart as a curiosity, a conversation starter or a fun way to compare dates with friends.
Frequently asked questions
What is a biorhythm?
Biorhythm theory, popular from the 1970s, claims that three regular cycles start at birth: a 23-day physical cycle, a 28-day emotional cycle and a 33-day intellectual cycle. Each one is drawn as a sine wave that swings between +100% and −100%.
How is a biorhythm calculated?
Count the days t since birth, then compute sin(2π × t ÷ period) × 100 for each cycle. For example, on day 10,000 the physical value is sin(2π × 10000 ÷ 23) × 100, about −98%.
What is a critical day?
A critical day is a day on which a cycle crosses the zero line, moving from its positive to its negative half or back. Believers say these days are unstable; there is no scientific evidence for that.
Are biorhythms scientifically proven?
No. Controlled studies have found no link between biorhythm cycles and performance, accidents or mood. Treat the results as entertainment, not as a basis for health, safety or other decisions.
What do positive and negative values mean?
In the theory, a positive value is a high phase (more energy, better mood or sharper thinking, depending on the cycle) and a negative value is a low or recharging phase. The overall score here is simply the average of the three main cycles.
When do the cycles all start again together?
The 23, 28 and 33-day cycles line up again after their least common multiple, 21,252 days, which is about 58.2 years after birth.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.