Enforcement Rules of the Household Registration Act Article 18
The age shown on the submitted certificate for correcting the birth date of household registration should be counted according to chronological age of country calendar. As to the certificate only with age, should use the certificate issuing date or ROC year minus the age to presume its birth year. However, the person born before the country establishing year should use the age on the certificate minus the year issued certificate or year established plus one to count his age.
中文原文 戶籍法施行細則第18條
更正出生年月日證件所載歲數，以國曆足歲計算。
證件僅載有歲數者，以其發證或建立之民國紀元減去所載歲數，推定其出生年次。
但民國前出生者，以證件所載歲數，減去發證或建立時之年份，再加一計算。
證件僅載有歲數者，以其發證或建立之民國紀元減去所載歲數，推定其出生年次。
但民國前出生者，以證件所載歲數，減去發證或建立時之年份，再加一計算。