This calendar is different from the one we use. This has been used as part of Chinese tradition in order to predict the gender of a child even before birth. The great thing about this calendar is that it has been shared to the rest of the globe and many have benefited from its accuracy.
There are cases wherein expecting parents would complain that it did not work for them. Most - if not all - of these failed predictions are not caused by the margin of error of the system. It failed because the required input was not accurate.
Expecting or planning couples have consulted this calendar for them to know what their future child's gender will be. While it is enticing to know that this system exists and that many have successfully used it, you have to keep in mind that there are numerous factors that can affect its results.
Another factor to consider is the month of conception. This is absolutely different from the date of birth. In conventional medicine, this can be determined by counting 9 months and 1 week back from the date of birth. If the child is yet to be born, this is counted from the date the mother had her last menstrual period. This is a crucial factor and cannot be confused. So if you want to be safe and sure as you consult this calendar, you may want to ask your gynecologist about determining your conception date.
Let's put it this way, you cannot be able to make a cup of coffee if you used orange juice instead of plain water. This means that if you factor in one wrong ingredient, the entire process falls apart. There are two key factors that are required to make a successful prediction using this calendar. These are the mother's age at the time of conception and the month of conception. However, the traditional calendar requires the mother to input her age according to the lunar calendar. This is different to our recognized age as the Chinese acknowledges the beginning of the year according to their own system and not every first of January.