Age Calculation Guide
Difference Between Full Age and East Asian Age
In daily life, people may answer age differently because multiple age-counting systems are used. This tool distinguishes full age and East Asian age.
Full age is the international legal standard. The rule is simple: age starts at 0 on the day of birth and increases by 1 on each birthday. Official documents such as passports and IDs use full age.
East Asian age is a traditional system used in East Asia. The common rule is: age starts at 1 at birth, then increases by 1 after each Lunar New Year. Because of that, East Asian age is usually 1-2 years higher than full age.
This tool uses the Lunar New Year boundary by default for East Asian age, which is the most common practical method.
Why Lunar Birthdays Need Conversion
The lunar calendar and Gregorian calendar are different time systems. Lunar dates shift against Gregorian dates each year and may include leap months.
If you only know your lunar birthday, conversion to Gregorian date is required before full-age and constellation calculations can be accurate. This tool includes complete lunar data from 1900 to 2100 and handles leap months automatically.
Zodiac Year Boundary Discussion
The Chinese zodiac uses a 12-animal cycle: Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog, Pig. There are two common boundary views:
- Lunar New Year boundary: mainstream rule. A new zodiac year starts on the first day of lunar new year. This is the default in this tool.
- Start of Spring boundary: some schools use the solar term “Start of Spring” as the boundary.
For people born around Lunar New Year, zodiac may differ from Gregorian year. This tool converts to lunar year first, then determines zodiac.
Constellation Date Ranges
Constellation is determined by Gregorian month/day:
| Constellation | English | Date Range |
|---|---|---|
| ♈ Aries | Aries | Mar 21 - Apr 19 |
| ♉ Taurus | Taurus | Apr 20 - May 20 |
| ♊ Gemini | Gemini | May 21 - Jun 21 |
| ♋ Cancer | Cancer | Jun 22 - Jul 22 |
| ♌ Leo | Leo | Jul 23 - Aug 22 |
| ♍ Virgo | Virgo | Aug 23 - Sep 22 |
| ♎ Libra | Libra | Sep 23 - Oct 23 |
| ♏ Scorpio | Scorpio | Oct 24 - Nov 22 |
| ♐ Sagittarius | Sagittarius | Nov 23 - Dec 21 |
| ♑ Capricorn | Capricorn | Dec 22 - Jan 19 |
| ♒ Aquarius | Aquarius | Jan 20 - Feb 18 |
| ♓ Pisces | Pisces | Feb 19 - Mar 20 |
Leap Year and Feb 29
Leap-year rule: years divisible by 4 are leap years, except years divisible by 100 unless also divisible by 400.
For birthdays on Feb 29, this tool calculates the next birthday as Mar 1 in non-leap years.
About This Tool
This age calculator supports both Gregorian and lunar input. It calculates full age, East Asian age, precise age (year-month-day), zodiac, constellation, days/hours lived, days until next birthday, and life progress.
All calculations run in your browser. No personal data is uploaded. Shared links include birth-date parameters, so share with care.