Chinese calendar year does not start on January 1st like that of Gregorian calendar. They have their own calculation based on Lunar cycles and mostly it starts from mid of January - like month of 'Thai' for Tamils. Sometimes, the year starts from middle February.
Chinese gender prediction is based on data available for about 300 years. The data was collected between 1644 - 1911 by imperial palace of Qing Dynasty and this Chinese Baby Gender Chart or Birth Chart was created.
In combination with I Ching, Eight Diagrams and other knowledge, the Chart can predict the baby gender.
Across the globe, comparing to Shettles Method (with basic scientific sense) or Mayan Gender Prediction calculator, Chinese gender prediction far-reaching influence, and also believed by many people.
Please note that, though people believe Chinese gender prediction chart that it shows a high level of accuracy, it is not a scientific method to predict baby gender. There is a chance of 50:50 error.
This calculator helps to calculate Mother's age according to Chinese Lunar calendar using the date of birth derived from Gregorian calendar. Same way, it calculates the Lunar Chinese month for the corresponding Gregorian month.