In this paper, the author refers the problems on the determination of the interest owed in accordance with the article 78 of the United Nations on Contracts for the International sale of Goods. In this paper there appear and develop the different solutions suggested by the doctrine, and adopted as arbitral and international courts. The work is based on the consultation of specializing doctrine, foreign jurisprudence and arbitral international awards. The diverse solutions stem from the variable form as there is interpreted the article 7 of the Convention, which indicates the way of filling gaps inside the same one.