'Zhōu suì' literally means 'full cycle of years' — 周 (zhōu) signifies a complete cycle or round, and 岁 (suì) means 'year' or 'age'. Together, they denote a person's exact, completed age in full years, calculated from birth to the current date — equivalent to 'years old' in Western counting. This is the standard age measurement used in official documents, medical records, school enrollment, and legal contexts in China.

Unlike traditional Chinese age reckoning (虚岁, xūsuì), where a person is considered one year old at birth and gains a year each Spring Festival, 周岁 reflects precise chronological age: a baby born on May 10 turns one 周岁 exactly on May 10 of the following year. It’s widely used in formal and everyday situations when accuracy matters — for example, determining eligibility for vaccinations, kindergarten entry, or driver’s license applications.