# Income

Income is the consumption and saving opportunity gained by an entity within a specified timeframe, which is generally expressed in monetary terms.[1][2][3]

For households and individuals, "income is the sum of all the wages, salaries, profits, interest payments, rents, and other forms of earnings received in a given period of time."[4] (also known as gross income). Net income is defined as the gross income minus taxes and other deductions (e.g., mandatory pension contributions), and is usually the basis to calculate how much income tax is owed.

In the field of public economics, the concept may comprise the accumulation of both monetary and non-monetary consumption ability, with the former (monetary) being used as a proxy for total income.

For a firm, gross income can be defined as sum of all revenue minus the cost of goods sold. Net income nets out expenses: net income equals revenue minus cost of goods sold, expenses, depreciation, interest, and taxes.[3]

## Economic definitions

In economics, "factor income" is the return accruing for a person, or a nation, derived from the "factors of production": rental income, wages generated by labor, the interest created by capital, and profits from entrepreneurial ventures.[5]

In consumer theory 'income' is another name for the "budget constraint," an amount ${\displaystyle Y}$ to be spent on different goods x and y in quantities ${\displaystyle x}$ and ${\displaystyle y}$ at prices ${\displaystyle P_{x}}$ and ${\displaystyle P_{y}}$. The basic equation for this is

${\displaystyle Y=P_{x}\cdot x+P_{y}\cdot y}$

This equation implies two things. First buying one more unit of good x implies buying ${\displaystyle {\frac {P_{x}}{P_{y}}}}$ less units of good y. So, ${\displaystyle {\frac {P_{x}}{P_{y}}}}$ is the relative price of a unit of x as to the number of units given up in y. Second, if the price of x falls for a fixed ${\displaystyle Y}$ and fixed ${\displaystyle P_{y},}$ then its relative price falls. The usual hypothesis, the law of demand, is that the quantity demanded of x would increase at the lower price. The analysis can be generalized to more than two goods.

The theoretical generalization to more than one period is a multi-period wealth and income constraint. For example, the same person can gain more productive skills or acquire more productive income-earning assets to earn a higher income. In the multi-period case, something might also happen to the economy beyond the control of the individual to reduce (or increase) the flow of income. Changing measured income and its relation to consumption over time might be modeled accordingly, such as in the permanent income hypothesis.

### Full and Haig-Simons income

"Full income" refers to the accumulation of both the monetary and the non-monetary consumption-ability of any given entity, such as a person or a household. According to what the economist Nicholas Barr describes as the "classical definition of income" (the 1938 Haig-Simons definition): "income may be defined as the... sum of (1) the market value of rights exercised in consumption and (2) the change in the value of the store of property rights..." Since the consumption potential of non-monetary goods, such as leisure, cannot be measured, monetary income may be thought of as a proxy for full income.[3] As such, however, it is criticized[by whom?] for being unreliable, i.e. failing to accurately reflect affluence (and thus the consumption opportunities) of any given agent. It omits the utility a person may derive from non-monetary income and, on a macroeconomic level, fails to accurately chart social welfare. According to Barr, "in practice money income as a proportion of total income varies widely and unsystematically. Non-observability of full-income prevent a complete characterization of the individual opportunity set, forcing us to use the unreliable yardstick of money income.