Biorhythm Calculator

What this calculator does

The biorhythm theory suggests that three cycles - physical, emotional, and intellectual - rise and fall like waves from the day you're born, repeating on fixed periods for your entire life. This calculator uses your date of birth and a target date to compute:

• your current Physical, Emotional, and Intellectual cycle percentages
• a plain-language summary of where each cycle stands today
• a checklist with practical notes for each cycle's current phase
• a 14-day forecast table so you can see upcoming highs, lows, and critical (transition) days

Formula Used

Each cycle is modeled as a sine wave based on the number of days you've been alive:

$$value = \sin\left(\frac{2\pi \times days}{period}\right) \times 100$$

Where days is the number of full days between your date of birth and the target date, and period is fixed per cycle:

• Physical cycle: 23 days
• Emotional cycle: 28 days
• Intellectual cycle: 33 days

The result is a percentage between -100 and +100 for each cycle. Positive values mean that cycle is in an upswing, negative values mean it's in a downswing, and values near zero (within ±5%) mark a "critical day" - the point where the cycle crosses from one phase to the other.

Reading the phases

Value range	Phase
50 to 100	Peak
5 to 49	Rising
-4 to 4	Critical
-49 to -5	Low
-100 to -50	Trough

Example

Someone born on 1995-06-15, checking their biorhythm on 2026-07-09, has been alive for 11,347 days. Plugging that into the formula for the physical cycle (period 23):

$$value = \sin\left(\frac{2\pi \times 11347}{23}\right) \times 100 \approx 82$$

That's a Physical score of about 82% - a "Peak" day, good for physical activity.

Notes

• Biorhythm theory is a popular pseudoscientific concept with no scientific backing - treat this as a fun, reflective tool rather than a medical or scientific instrument.
• The forecast table starts from your selected target date and shows the next 14 days, so you can plan around upcoming peaks and critical days.