Biorhythm Calculator

Draws your physical, emotional and intellectual biorhythms from your date of birth, with today's values and curves for 30 days either side. You can also overlay a second person's rhythms and see how closely they match.

How to use

1. Enter your "Date of birth" to see today's physical, emotional and intellectual values in percent, each marked as a high phase, low phase or critical day.
2. Change the "Date to view", or use "Previous day", "Next day", "Week before" and "Week after". Tapping the chart also moves to that date.
3. Tick "Compare with someone" and enter "Their date of birth" to draw both sets of curves and see the "Rhythm match".

How it works

• Counting the birth date as day 0, each value is sin(2π × days ÷ period). The periods are 23 days (physical), 28 days (emotional) and 33 days (intellectual).
• The day nearest to the point where a curve crosses zero is marked as a critical day.
• Biorhythms are calculated for fun; there is no confirmed scientific basis for them.

Questions and answers

What is a critical day in biorhythms?

A day when a rhythm crosses between plus and minus. It comes every half period: every 11.5 days for physical, 14 days for emotional and 16.5 days for intellectual, so physical critical days alternate 11 and 12 days apart and intellectual ones 16 and 17 days apart. Emotional critical days always fall on the weekday you were born.

What do 100% and -100% mean?

They are the highest and lowest points of a curve. Above 0 is shown as a high phase and below 0 as a low phase, and the card also says whether the rhythm is "Rising" or "Falling".

How is biorhythm compatibility calculated?

For a gap of Δ days between two birthdays, the match is (1 + cos(2πΔ ÷ period)) ÷ 2. If the gap is a multiple of 28 days, the emotional match is 100%. The value is the same on every date.

Are biorhythms scientifically accurate?

No scientific basis for them has been confirmed. Treat the results as entertainment only.