Disposable income is the amount of an individual's total income left after taxes, plus any transfer payments (grants) received from the government or elsewhere, which is available for spending and saving. It is distinguished from discretionary income which is disposable income minus fixed consumption costs (such as rent/mortgage, food, car payments, insurance, etc.)
The latter is income that you spend on things that you want, not the money you spend on what you need.
See also
External link
A simple disposable income calculator