One of the most common surprises for people learning about the Chinese zodiac is discovering that their birth year sign is not what they assumed. This happens because the Chinese zodiac year does not begin on January 1. It begins on Lunar New Year, which is the second new moon after the winter solstice — a date that drifts each year through late January and February.
If you were born in January or in the first half of February, your zodiac sign is determined by whether your birthday falls before or after that year's Lunar New Year. Someone born on January 28, 1990, for example, was born during the year of the Snake (1989's lunar year continued until January 27, 1990). Someone born on February 28, 1990 was born in the year of the Horse, because Lunar New Year 1990 fell on January 27. Looking up your exact lunar birth date is the only reliable way to know your sign for certain.
The lunar calendar matters for more than just sign assignment. Many of the most auspicious days in Chinese astrology — the new moon (a day for setting intentions), the full moon (a day for completion and release), the lunar new year (a fresh start for everyone), and the mid-autumn festival (a day for family and reflection) — track lunar phases rather than solar ones. Reading your daily fortune in alignment with the actual lunar cycle, rather than the Gregorian calendar, often produces more precise and useful guidance. If you have only ever read your sign through the Western calendar, you have been reading half the picture.