Haram. It can be categorized under riba.
There are two kinds of Riba: Riba al-Nasi'ah, and Riba al-Fadl.
Riba al-Nasi'ah
The term nasi'ah means to postpone, defer, or wait and refers to the time that is allowed for the borrower to repay the loan in return for the addition or the premium. Hence Riba al-Nasi'ah refers to the interest on the loan. It is in this sense that the term Riba has been used in the Qur'an in the verse "God has forbidden interest" (2: 275). This is also the Riba which the prophet, peace be on him, referred to when he said: "There is no Riba except in nasi'ah."