A half birthday marks the date exactly six months from an individual’s birth date. For example, someone born on March 10th would celebrate this occasion on September 10th. It’s a derivative celebration, rooted in the original anniversary of one’s birth.
The observance of a half birthday can offer an opportunity for additional celebration spread throughout the year, particularly for those whose actual birthdays fall during holidays or other busy periods. It can serve as a smaller, less formal occasion to acknowledge someone’s age or existence. There isn’t substantial documented historical context, suggesting it is a modern, informal tradition.