In the twelfth and final season, Penny announces that she doesn't want to have any children which Leonard somewhat reluctantly supports her decision. Later Penny's old boyfriend Zack Johnson and his new wife want Leonard to be a surrogate father to their kid since Zack is infertile. Penny reluctantly agrees to let Leonard do it until Leonard finally changes his mind not wanting a child in the world that he can't raise. At the end of the season; however, Penny accidentally gets pregnant with Leonard's child, and changes her mind about wanting children.