In accounting, fixed capital is any kind of real, physical asset that is used repeatedly in the production of a product. In economics, fixed capital is a type of capital good that as a real, physical asset is used as a means of production which is durable or isn't fully consumed in a single time period. It contrasts with circulating capital such as raw materials, operating expenses etc.

The concept was first theoretically analyzed in some depth by the economist Adam Smith in The Wealth of Nations (1776) and by David Ricardo in On the Principles of Political Economy and Taxation (1821). Ricardo studied the use of machines in place of labor and concluded that workers' fear of technology replacing them might be justified.

Thus fixed capital is that portion of the total capital outlay that is invested in fixed assets (such as land improvements, buildings, vehicles, plant, and equipment), that stay in the business almost permanently—or at the very least, for more than one accounting period. Fixed assets can be purchased by a business, in which case the business owns them. They can also be leased, hired or rented, if that is cheaper or more convenient, or if owning the fixed asset is practically impossible (for legal or technical reasons).

Refining the classical distinction between fixed and circulating capital in Das Kapital, Karl Marx emphasizes that the distinction is really purely relative, i.e. it refers only to the comparative rotation speeds (turnover time) of different types of physical capital assets. Fixed capital also "circulates", except that the circulation time is much longer, because a fixed asset may be held for 5, 10 or 20 years before it has yielded its value and is discarded for its salvage value. A fixed asset may also be resold and re-used, which often happens with vehicles and planes.

In national accounts, fixed capital is conventionally defined as the stock of tangible, durable fixed assets owned or used by resident enterprises for more than one year. This includes plant, machinery, vehicles and equipment, installations and physical infrastructures, the value of land improvements, and buildings.

The European system of national and regional accounts (ESA95) explicitly includes produced intangible assets (e.g. mineral exploitation, computer software, copyright protected entertainment, literary and artistics originals) within the definition of fixed assets.

Land itself is not included in the statistical concept of fixed capital, even though it is a fixed asset. The main reason is that land is not regarded as a product (a reproducible good). But the value of land improvements is included in the statistical concept of fixed capital, is regarded as the creation of value-added through production.