The authentic Chinese Gender Chart does not change from year to year and is based on the lunar month calendar, which China used before adopting the Gregorian calendar in the 20th century. A lunar month is the amount of time it takes for the moon to complete a 29 ½-day cycle. The Gregorian calendar is about 11 days shorter because it is based on the sun’s cycle, instead. When a baby is born, it is already a year old according to the lunar calendar.

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