Bertinelli was born in Wilmington, Delaware to Nancy (née Carvin) and Andrew Bertinelli, a General Motors executive. Her father is of Italian descent and her mother is of English descent. She has three brothers: David, Patrick and Drew. She had an elder brother, Mark, who died at 17 months from an accidental poisoning before she was born. Because of her father's career, the family frequently moved. Over various periods, they lived in Claymont, Delaware; Clarkston, Michigan; Shreveport, Louisiana; Oklahoma City and the Los Feliz section of Los Angeles, California, where Bertinelli studied acting at the Tami Lynn School of Artists. She attended Granada Hills High School. She was raised Roman Catholic.