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Biorhythm Calculator
Chart the physical, emotional and mental cycles for any date from your birthday.
Your biorhythm chart
Days since birth: —
Physical (23 days): —
Emotional (28 days): —
Mental (33 days): —
Total cycle length: —
How to use the Biorhythm Calculator
- Enter your birth date to set the cycle origin.
- Choose the chart date, or click Use today to jump to today.
- Read the three cycle values and the fifteen day chart on either side of that date.
Features
- Classic 23, 28 and 33 day sine cycles
- Chart drawn on a canvas with fifteen days either side
- High, low and critical day labels
- Runs locally, no uploads
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Frequently Asked Questions
Common questions about the free online biorhythm calculator.
It is the idea that physical, emotional and mental energy follow regular sine cycles that
start on the day you were born.
The classic lengths are twenty-three days for the physical cycle, twenty-eight for the
emotional cycle and thirty-three for the mental cycle.
The tool takes the whole days since birth and puts that number through a sine wave with the
cycle length, giving a value from minus one to plus one.
A critical day is where a cycle crosses the centre line, so the value is near zero and the
cycle is changing direction.
A high day sits near the top of the wave, where the value is close to plus one and the cycle
is said to be at its strongest.
The three lengths share no common factors, so their combined pattern repeats only after their
lowest common multiple, which is 21252 days.
No. Controlled studies have not shown that biorhythms predict performance, so treat the chart
as a curiosity rather than evidence.
No. The chart is drawn in your browser and your birth date never leaves your device.
Yes. The canvas is scaled to the width of the page, so the chart stays readable on phones,
tablets and desktops.
Yes. It is completely free, needs no account and has no limit on how many dates you chart.
Last updated: October 10, 2026