sui 歲, the traditional lunar age

The traditional lunar age calculation operates with "void years" (xusui 虛歲). This method uses calendric years to indicate the age of a person. When born, a person is one "year" (sui 歲) old, not because he or she has spent 9 months in the womb of the mother (as popular belief goes), but because the current year is the first calendric year the person experiences. With the shift to the next calendric year (according to the Chinese calendar), the person in question is two "years" (sui) old, even if he or she was born only a week or a day before the Chinese New Year. The consequence is that the difference between the lunar age and the real age (shisui 實歲, measured in absolute time) can be as much as one, sometimes even two "years". A person in a traditional text, having the age of 20 sui, is thus 19 or 18 years (absolute) old.