The authors agree that this surname has its base in the medieval name of auspicious character Bonaiutus or Bonaita, composed of bon / buon ("good") and aita / aiuto ("help"), attributed to newborns in the hope that they would be a good help to the family. E. De Felice documents these forms in Tuscany from the 11th century and notes that the surname spreads from that region to Emilia and Lombardy, also appearing sporadically in southern Italy.

E. Rossoni specifies the geographical distribution: he identifies a cluster in Tuscany, concentrated in Florence and its nearby area (Prato, Pontassieve, Sesto Fiorentino, Calenzano), with presence also in the Bologna area; and another in eastern Lombardy, in the Lecco areas (Calolziocorte, Carenno, Torre de' Busi) and Bergamo (San Giovanni Bianco, San Pellegrino Terme, Cisano Bergamasco, Caprino Bergamasco).

As for variants, De Felice highlights that Bonaiuto is fairly common in the Naples area. Rossoni distinguishes in greater detail: Buonaiuto is extremely rare and peculiar to Florence; Bonaiuto is typical of Sarno, in the Salerno area, with an important cluster also in Naples and its province; and another homonymous form is characteristic of Sicily, especially of the Syracuse area, with additional clusters in Nicosia (province of Enna) and Pachino.