In economics or macroeconomics

In economics or macroeconomics



economic theory or in macroeconomics, investment is the amount purchased per unit time of goods which are not consumed but are to be used for future production (i.e. capital). Examples include railroad or factory construction. Investment in human capital includes costs of additional schooling or on-the-job training. Inventory investment is the accumulation of goods inventories; it can be positive or negative, and it can be intended or unintended. In measures of national income and output, "gross investment" (represented by the variable I) is also a component of gross domestic product (GDP), given in the formula GDP = C + I + G + NX, where C is consumption, G is government spending, and NX is net exports, given by the difference between the exports and imports, X − M. Thus investment is everything that remains of total expenditure after consumption, government spending, and net exports are subtracted (i.e. I = GDP − C − G − NX).
Non-residential fixed investment (such as new factories) and residential investment (new houses) combine with inventory investment to make up I. "Net investment" deducts depreciation from gross investment. Net fixed investment is the value of the net increase in the capital stock per year.
Fixed investment, as expenditure over a period of time ("per year"), is not capital. The time dimension of investment makes it a flow. By contrast, capital is a stock— that is, accumulated net investment to a point in time (such as December 31).
Investment is often modeled as a function of Income and Interest rates, given by the relation I = f(Y, r). An increase in income encourages higher investment, whereas a higher interest rate may discourage investment as it becomes more costly to borrow money. Even if a firm chooses to use its own funds in an investment, the interest rate represents an opportunity cost of investing those funds rather than lending out that amount of money for interest.