This invention is a new and distinct grapevine variety denominated ‘IFG Twenty-eight’. The new grapevine is characterized by producing naturally medium large, round to slightly elliptic, seedless berries having a small seed trace that is normally not noticeable. Berries are medium firm in texture and ripen in mid-season. Fruits normally ripen in early August, about with or just slightly earlier than the Thompson Seedless variety near Delano, Calif.