The Chinese Pregnancy Calendar helps a would-be mother to determine the gender of her baby based on her date of birth and date of conception. The logic of this calendar helps you to plan your pregnancy based on your preference to have a boy or a girl. The origin of the Chinese calendar can be traced back to the 14th century B.C. Although it is said to be the Chinese Lunar Calendar, it is actually a lunisolar calendar which is based on the rotational properties of both the Sun as well as the Moon. As this calendar is based upon the true and accurate orbital positions of the Sun and the Moon, the accuracy and precision of this very calendar depends upon the astronomical theories and the formulae used.