The application of jizya varied in the course of Islamic history. Together with kharāj, a term that was sometimes used interchangeably with jizya, taxes levied on non-Muslim subjects were among the main sources of revenues collected by some Islamic polities, such as the Ottoman Empire and Indian Muslim Sultanates. Jizya rate was usually a fixed annual amount depending on the financial capability of the payer. Sources comparing taxes levied on Muslims and jizya differ as to their relative burden depending on time, place, specific taxes under consideration, and other factors.