You see what year you were born, and then what day is the corresponding Gregorian calendar in that year. Finally, which constellation is the date range of the following constellation, you are that constellation.
Capricorn (12/22-119)
AquariusNo. (1/20-2/ 18)
Pisces (2/ 19-3/20)
Aries (3/2 1-4/20)
Taurus (4/2 1-5/20)
Gemini (5/2 1-6/2 1)
Cancer (June 22-July 22)
Leo (July 23-August 22)
Virgo (August 23-September 22)
Libra (9/23- 10/22)
Scorpio (10/23-11/21)
Sagittarius (11/22-12/21)