This is determined by disposable personal income( personal income minus direct taxes and other deductions ). Some people suggest the use of discretionary income in place of disposable income. Discretionary income can be estimated by subtracting three items from disposable income viz.... inputed income in kind major fixed outlay payments such as mortgage debt payments insurance premium payments and rent and essential expenditure such as food and clothing and transport expenses based upon consumption in a normally year. Discretionary income can be quite an important determinant in case of consumer non durables which are luxuries.