Disposable income is total personal income minus personal current taxes.[1] In national accounts definitions, personal income, minus personal current taxes equals disposable personal income.[2] Subtracting personal outlays (which includes the major category of personal (or, private) consumption expenditure) yields personal (or, private) savings.
Restated, consumption expenditure plus savings equals disposable income[3] after accounting for transfers such as payments to children in school or elderly parents’ living arrangements.[4]
The marginal propensity to consume (MPC) is the fraction of a change in disposable income that is consumed. For example, if disposable income rises by $100, and $65 of that $100 is consumed, the MPC is 65%. Restated, the marginal propensity to save is 35%.
Discretionary income is money remaining after all bills are paid off. It is income after subtracting taxes and normal expenses (such as rent or mortgage, utilities, insurance, medical, transportation, property maintenance, child support, inflation, food and sundries, etc.) to maintain a certain standard of living.[5] It is the amount of an individual's income available for spending after the essentials (such as food, clothing, and shelter) have been taken care of:
Despite the definitions above, disposable income is often incorrectly used to denote discretionary income. The meaning should therefore be interpreted from context. Commonly, disposable income is the amount of "play money" left to spend or save. The Consumer Leverage Ratio is the expression of the ratio of Total Household Debt to Disposable Income.
When applying for a loan (mortgage, consumer loan), lenders may take into consideration a high-income applicant's discretionary income in order to assess the loan repayment capacity of the applicant. Discretionary income provides the lender with more information on the applicant's capacity to repay than the debt-to-income ratio in the case where the applicant has a lot of debt, but also a lot of income, such that the percent of available income may be smaller than normal standards would allow, but the actual amount of money is still large.[6]