What a half birthday is
Your half birthday is six months after your birthday: May 14 becomes November 14. It's a good excuse for a small celebration, and in schools it's a popular way to celebrate kids whose real birthday falls during the summer break.
End-of-month birthdays
Six calendar months after August 31 is the last day of February, so the half birthday is February 28, or February 29 in a leap year. For a February 29 birthday, the half birthday is August 29.
Six months or 182 days?
Half of a 365-day year is 182.5 days, so some people count 182 or 183 days instead of six calendar months. Depending on the months in between, that lands up to two days earlier or one day later. The result shows both, so you can pick the one you prefer.