Biorhythms Guide is a dialog-based application which calculates (using Kotelnic''s method) the dates of the so called days of tiredness. Kotelnic''s method uses the refined values of physical emotional and intellectual biorhythm period lengths (for example the length of emotional biorhythm period constitutes 28.4261246 days ). The method also takes into consideration biorhythms with the periods equal to 1/2 of the fundamental biorhythms periods. This "short" biorhythms are just responsible for days of tiredness. Biorhythms Guide allows you to predict the dates of vital power decrease and prevent or at least minimize undesirable consequences. The program calculates also the dates of new moon and full moon and expose their pictures if this date is in a vicinity of a day of tiredness. Biorhythms Guide allows you to compare vital power of two persons. The software features a simple user-friendly interface and short yet detailed help which includes the overview of the biorhythms fundamental basis.