Biorhythm Calculator

Biorhythm theory proposes that human physical, emotional, and intellectual states follow predictable sinusoidal cycles from birth. Though not recognized by mainstream science, biorhythms remain a popular tool for personal planning and self-awareness.

The three core biorhythm formulas: Physical(d) = sin(2π × d / 23) Emotional(d) = sin(2π × d / 28) Intellectual(d) = sin(2π × d / 33)

Where:

• d = number of days elapsed since birth date
• 23 = physical cycle period (days), governs stamina, coordination, and strength
• 28 = emotional cycle period (days), governs mood, creativity, and emotional sensitivity
• 33 = intellectual cycle period (days), governs analytical thinking, memory, and decision-making

Each formula produces values between −1.0 (lowest point) and +1.0 (peak). A value of 0 is called a critical day — a transition point associated with instability in that dimension.

Cycle phases:

• +0.5 to +1.0 → high phase: favorable time for activities in that domain
• −0.5 to −1.0 → low phase: rest, avoid high-risk decisions in that domain
• Near 0 → critical day: unpredictable transitions

Worked example: A person born January 15, 1990, checking their biorhythms on April 8, 2026: Days elapsed = 13,232 Physical = sin(2π × 13,232 / 23) = sin(3,618.7 rad) ≈ +0.74 (high) Emotional = sin(2π × 13,232 / 28) = sin(2,972.3 rad) ≈ −0.45 (low) Intellectual = sin(2π × 13,232 / 33) = sin(2,520.0 rad) ≈ +0.12 (near critical)

Composite score: average of all three = (0.74 − 0.45 + 0.12) / 3 ≈ +0.14 — a moderately stable day overall. Best used as a rough self-reflection guide, not a deterministic forecast.