Biorhythms are three sine-wave cycles: physical (23 days), emotional (28 days), intellectual (33 days). They were popularized in the 1970s but have no scientific evidence.

What are critical days?

The days when a cycle crosses zero—physical, emotional, or intellectual. Some believe these are days of reduced performance or coordination.

Who invented biorhythms?

Wilhelm Fliess (1897) proposed 23-day physical and 28-day emotional cycles. Alfred Teltscher added the 33-day intellectual cycle.

How is the value calculated?

Value = sin(2π × daysAlive / cycle) × 100. Range is -100% to +100% for each cycle.

The numbers were chosen by early proponents. 28 is the lunar cycle; 23 and 33 have no special scientific basis.

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PREDICTIONFun & GamesQuirky Calculator

📊

Your Biorhythm Cycles

Physical (23 days), emotional (28 days), intellectual (33 days)—three sine waves that supposedly predict your energy, mood, and mental sharpness. For entertainment only; no scientific evidence supports biorhythms.

Concept Fundamentals

-88.8%

Physical

Emotional

86.6%

Intellectual

13,244

Days Alive

Calculate BiorhythmsUse the tools below to explore something different

✨ The Fun Behind This

Why It's Fun

Biorhythm theory was popularized in the 1970s. Wilhelm Fliess proposed 23/28-day cycles; Alfred Teltscher added the 33-day intellectual cycle. Controlled studies found no correlation with real performance.

How It Works

Each cycle is a sine wave: value = sin(2π × daysAlive / cycle) × 100. Range -100% to +100%. Positive = peak, negative = low, zero = critical day.

Key Insights

●Physical 23 days — energy, strength, coordination.
●Emotional 28 days — mood, creativity, intuition.
●Intellectual 33 days — logic, focus, learning.
●Biorhythms are pseudoscience—use for fun only!

Sources:Wilhelm Fliess Skeptic's Dictionary

📈

FUN & GAMES

Biorhythm Calculator — Physical, Emotional, Intellectual

23-day physical, 28-day emotional, 33-day intellectual cycles. Sine-wave values from -100% to +100%. For entertainment only!

📈 Quick Examples — Click to Load

Inputs

Birthdatee.g. 1990-01-15

Target DateDate to calculate for

biorhythm.txt

CALCULATED

$ biorhythm --birth=1990-01-15 --target=2026-04-20

Physical (23d)

-88.8%

Emotional (28d)

Intellectual (33d)

86.6%

Days alive: 13,244

📐 Calculation Breakdown

INPUT

Birthdate

1990-01-15

Target Date

2026-04-20

CALC

Days Alive

13,244

( ext{target} - ext{birth}) / 86400000

RESULTS

Physical (23d)

-88.8%

\text{sin}(2\text{pi} imes ext{days}/23) imes 100

Emotional (28d)

\text{sin}(2\text{pi} imes ext{days}/28) imes 100

Intellectual (33d)

86.6%

\text{sin}(2\text{pi} imes ext{days}/33) imes 100

For educational and informational purposes only. Verify with a qualified professional.

🎲 Fun Facts

📅

Biorhythm theory was popularized in the 1970s—many watched their "critical days".

— Pop culture

🔬

Controlled studies found no correlation between biorhythm predictions and real performance.

— Skeptic's Dictionary

📐

Each cycle is a sine wave: value = sin(2π × days/cycle) × 100.

— Math

📋 Key Takeaways

• Physical cycle: 23 days — energy, strength, coordination
• Emotional cycle: 28 days — mood, creativity, intuition
• Intellectual cycle: 33 days — logic, focus, learning
• Each cycle is a sine wave from -100% to +100%
• Biorhythms are a pseudoscience — no scientific evidence supports them. Use for fun only!

💡 Did You Know?

📅Biorhythm theory was popularized in the 1970s — many watched their "critical days"Source: Pop culture

🔬Controlled studies found no correlation between biorhythm predictions and real performanceSource: Skeptic's Dictionary

📐The 28-day emotional cycle matches the average menstrual cycle — possibly why it was chosenSource: History

🌊Each cycle is a pure sine wave — mathematically elegant but biologically unsupportedSource: Math

⚠️"Critical days" occur when a cycle crosses zero — said to be riskier (unproven)Source: Theory

🎯Wilhelm Fliess (1897) proposed 23 and 28; Alfred Teltscher added 33 in the 1920sSource: Origins

📖 How It Works

Biorhythm theory assumes three sine-wave cycles start at birth. For each cycle, the value = sin(2π × daysAlive / cycleLength) × 100. Positive = "high" day; negative = "low" day.

Formula

value = sin(2π × daysSinceBirth / cycle) × 100

Physical: 23 days. Emotional: 28 days. Intellectual: 33 days.

🎯 Expert Tips

💡 Use for Fun Only

Enjoy the patterns, but don't make life decisions based on biorhythms. No scientific backing.

💡 Compare Dates

Change the target date to see how values shift. All three cycles have different periods.

💡 Critical Days

When a cycle crosses zero, theorists call it a "critical day." Unproven — treat as folklore.

💡 Share Results

Use Copy or Share to post your biorhythm snapshot. Great conversation starter.

⚖️ Cycle Comparison Table

Cycle	Days	Associated With	Origin
Physical	23	Energy, strength, coordination	Fliess 1897
Emotional	28	Mood, creativity, intuition	Fliess 1897
Intellectual	33	Logic, focus, learning	Teltscher 1920s

❓ Frequently Asked Questions

What are biorhythms?

Biorhythms are a theory that three cycles (physical, emotional, intellectual) affect our daily lives. Each follows a sine wave from birth.

Are biorhythms scientific?

No. Studies have found no correlation between biorhythm predictions and real outcomes. It is considered pseudoscience.

Why 23, 28, and 33 days?

These numbers were chosen by early biorhythm theorists. The 28-day emotional cycle coincides with the average menstrual cycle length.

What do positive vs negative values mean?

Positive values are said to indicate "high" days; negative "low" days. Critical days occur when a cycle crosses zero.

Can I use this for scheduling?

We do not recommend it. There is no evidence biorhythms predict performance. Use for entertainment only.

How often do all three align?

The least common multiple of 23, 28, 33 is 21,252 days (~58 years). All three peak together very rarely.

What is a critical day?

When a cycle crosses zero (transition from + to - or vice versa). Theorists claim these are riskier days — unproven.

📊 Biorhythm Stats

Physical Cycle (days)

Emotional Cycle (days)

Intellectual Cycle (days)

-100 to +100

Value Range %

📚 Sources

Wilhelm Fliess ↗

Origin of 23/28 day cycles

Alfred Teltscher ↗

33-day intellectual cycle

Skeptic's Dictionary ↗

Critical analysis of biorhythms

⚠️ Disclaimer: Biorhythms are pseudoscience with no scientific evidence. This calculator is for entertainment only. Do not use for scheduling, medical, or life decisions.

👈 START HERE

⬅️Jump in and explore the concept!

Your Biorhythm Cycles

✨ The Fun Behind This

Why It's Fun

How It Works

Key Insights

Biorhythm Calculator — Physical, Emotional, Intellectual

📈 Quick Examples — Click to Load

Inputs

Biorhythm Cycle Values

📐 Calculation Breakdown

🎲 Fun Facts

📋 Key Takeaways

💡 Did You Know?

📖 How It Works

Formula

🎯 Expert Tips

💡 Use for Fun Only

💡 Compare Dates

💡 Critical Days

💡 Share Results

⚖️ Cycle Comparison Table

❓ Frequently Asked Questions

What are biorhythms?

Are biorhythms scientific?

Why 23, 28, and 33 days?

What do positive vs negative values mean?

Can I use this for scheduling?

How often do all three align?

What is a critical day?

📊 Biorhythm Stats

📚 Sources

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Your Biorhythm Cycles

✨ The Fun Behind This

Why It's Fun

How It Works

Key Insights

Biorhythm Calculator — Physical, Emotional, Intellectual

📈 Quick Examples — Click to Load

Inputs

Biorhythm Cycle Values

📐 Calculation Breakdown

🎲 Fun Facts

📋 Key Takeaways

💡 Did You Know?

📖 How It Works

Formula

🎯 Expert Tips

💡 Use for Fun Only

💡 Compare Dates

💡 Critical Days

💡 Share Results

⚖️ Cycle Comparison Table

❓ Frequently Asked Questions

What are biorhythms?

Are biorhythms scientific?

Why 23, 28, and 33 days?

What do positive vs negative values mean?

Can I use this for scheduling?

How often do all three align?

What is a critical day?

📊 Biorhythm Stats

📚 Sources

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We Value Your Privacy