Born on the Cusp - Zodiac Cusp Dates - askAstrology An individual is "on the cusp" of a sign if he or she was born on the 18 th, 19 th, 20 th, 21 st, 22 nd, or 23 rd of a month. During those dates the Sun will ingress (or transition) from one zodiac sign to another, making the time of birth as important as the day of birth.. Consider a person born on October 23 rd at 2:37 pm in Cary, North Carolina; he or she would have a Libra Sun sign at ...