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The science of Biorhythms was attributed to the famous psychiatrist Sigmund Freud and his associates Dr Wilhelm Fliess and psychologist Dr Hermann Swoboda. They hypothesised that Biorhythms might determine the highs and lows of our life based on our birth date. The Biorhythms comprises three cycles: a 23-day physical cycle, a 28-day emotional cycle and a 33-day intellectual cycle.

Cycle Calculation

Two parameters are required to calculate the three cycles: your birth date and the date to start calculations. Each cycle is calculated as a sine wave using the following equations:

  • Physical = sin (2Πt / 23)
  • Emotional = sin (2Πt / 28)
  • Intellectual = sin (2Πt /33)

Where Π = Pi and t = is the number of days since birth

The three calculated sine waves are then plotted on a graph - see the "Biorhythms" diagram below.

Interpretation of the cycles

The diagram below represents the three sine waves for the cycles based on the birth date for 30 days, where the one on the X-axis (midline) is the given start date.


When the sine wave of a cycle is above the midline (x-axis) of the graph, we may experience a "High" in that cycle, e.g. for the intellectual cycle, your thought processes may be sharper, concentration easier, and you may have lots of ideas. When the sine wave of a cycle is below the midline of the graph, we may experience a "Low" in that cycle, e.g. for the Physical cycle, and we may feel weak and listless. Viewing the three cycles for the 7 (on the midline), we have Emotion and Intellectual are both High and Physical is Low in the diagram above.

On the diagram above, the 9 (on the midline) looks like a critical period physically as the Physical sine wave crosses the midline. When a sine wave crosses the midline, this is a crucial time in the corresponding rhythm, e.g. for the Emotional cycle, and you may feel irritable and sad and have emotional outbreaks. If two sine waves cross the midline simultaneously, this is a very critical time.

Biorhythms - Fact or Fiction?

A study by Quigley (1981)[1] involved the alleged relationship between biorhythms and sport. The study looked at all world record-breaking male athletes in track and field events from 1913 to 1977, and for specific circumstances, there was evidence to support biorhythms. In a study by Hines (1998)[2], which involved examining some 134 biorhythm studies, the study concluded that the biorhythms theory is not valid.

Try it Yourself

To find out what the next seven days may have installed for you, enter your date of birth and then select the Calculate Button.

  Year Month Day
Date of Birth  

Free Calculator

  • Biorhythms Calculator - a free Microsoft Excel spreadsheet that you can download and use on your computer. The spreadsheet will plot your biorhythms for the next 30 days.


  1. QUIGLEY, B. (1981) Biorhythms Cause Australian - N.Z. Tensions, The Skeptic, 1 (1), p. 2
  2. HINES, T. (1998) Comprehensive Review of Biorhythm Theory, Psychological Reports, 83, p. 19-64.

Page Reference

If you quote information from this page in your work, then the reference for this page is:

  • MACKENZIE, B. (2013) Biorhythms [WWW] Available from: [Accessed