Chinese Age Calculator: Traditional Sui and Completed Age

How to read it

Two people can give different ages for the same person without either having made an arithmetic mistake. The usual completed-age convention counts full years lived: it starts at zero and changes on the birthday. The traditional Chinese sui convention counts the birth period as the first year and advances the count for everyone when Lunar New Year begins.

The Lunar New Year date moves from year to year, so a reliable calculator cannot simply add one to the Gregorian year difference. This tool converts the birth date and reference date through the Chinese calendar and compares their related lunar years. A person born shortly before Lunar New Year can therefore be one sui at birth and two sui only days later while still being zero completed years old.

Historical Chinese population registers commonly recorded sui rather than exact completed age. Modern legal, medical, school, employment, and identity records normally require completed age or an exact date of birth. When a form asks for legal age, do not substitute the traditional count unless the form explicitly defines it that way.

This calculator is a calendar reference only. It does not estimate conception, pregnancy, fetal age, personality, health, compatibility, luck, or future events. Dates stay in the browser. For a lunar birthday, zodiac year, or full twelve-palace chart, use the separate tools because those answer different questions and may use different documented year boundaries.