🎂 Birthday Info Calculator
Accepts Gregorian (YYYY-MM-DD) or ROC year format (e.g. 79-05-20)
What This Tool Does
Enter one birth date and get the full picture: the Gregorian and ROC (Taiwan calendar) dates, exact age in years/months/days, both Western and East Asian age counts, the Chinese zodiac animal, the Western star sign, and the complete lunar-calendar date with Heavenly Stems and Earthly Branches. Everything is computed in your browser — your birth date never leaves your device.
East Asian Age Reckoning, Explained
In the traditional East Asian system you are born at age one (counting the time in the womb, by one telling), and everyone gains a year together at Lunar New Year — not on their birthday. A baby born a week before Lunar New Year turns "two" within days of birth. This system is still alive in temple rituals, fortune-telling, and casual conversation across Taiwan, and it's why someone's stated age can run one or two years ahead of their passport age.
The gap is closing officially, though: South Korea, the last country using it for legal purposes, switched its legal standard to international age in June 2023. When a form in Taiwan asks for 實歲 it means international age; 虛歲 is the traditional count this tool shows alongside it.
Why Your Chinese Zodiac Might Not Be What You Think
The zodiac year begins at Lunar New Year, which floats between late January and late February — not on January 1. So a "1990 baby" born on January 20, 1990 is actually a Snake (1989's animal), because the Year of the Horse only began on January 27 that year. If you were born in January or early February, always check against the actual Lunar New Year date; this tool does that for you automatically.
A further subtlety: Chinese astrology (BaZi) uses the solar-term calendar and draws the line at lichun (start of spring, ~February 4) instead. Different sites may therefore disagree for early-February birthdays — neither is "wrong," they follow different conventions. This tool uses the mainstream Lunar New Year boundary.
The 60-Year Cycle Behind "庚午" and Friends
The lunar result includes Stems-and-Branches (ganzhi) labels: ten Heavenly Stems combine with twelve Earthly Branches into a repeating cycle of 60 — applied to years, months, and days alike. It's the world's oldest continuously used calendar cycle, and it's why a 60th birthday is a landmark celebration across East Asia: you've completed one full cycle and returned to the ganzhi of your birth year.
Frequently Asked Questions
What is the ROC date the tool shows?
Taiwan's official calendar counts years from 1912, the founding of the Republic of China: ROC year = Gregorian year − 1911. It appears on Taiwanese IDs, licenses, and government forms. You can also type an ROC-format date (e.g. 79-05-20 for 1990-05-20) straight into the input.
How does the lunar calendar stay aligned with the seasons?
Lunar months follow the moon (~29.5 days), giving a ~354-day year. To stop drift, a leap month is inserted roughly every 2–3 years — some lunar years have 13 months. People born in a leap month usually celebrate in the regular month of the same name.
Is the Western star sign affected by any of this?
No — Western zodiac signs are purely solar, fixed to Gregorian date ranges (Aries starts March 21, and so on). Only the Chinese zodiac depends on the lunar year.
What about February 29 birthdays?
Leap-day babies are fully supported. In non-leap years the age rollover is counted at February 28, matching common legal practice.