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The '''depreciation of capital''' refers to the decline over time in the value of physical capital goods, such as machinery, equipment, buildings, and infrastructure, as a result of wear and tear, obsolescence, or accidental damage. In national accounts and economics, depreciation, also called consumption of fixed capital, measures the amount of capital that must be replaced to maintain the productive capacity of the capital stock. It is distinct from the depreciation of a currency, which refers to a fall in the exchange rate.

== Nature and causes ==

Capital goods lose value for several reasons. '''Physical deterioration''' occurs through use and exposure to the elements. '''Obsolescence''' arises when technological progress or changes in demand make existing capital less productive or uneconomic, even if it remains physically functional. '''Accidental damage''' and '''depletion''' of natural resources also reduce capital value. The rate at which capital depreciates varies widely by asset type: computer equipment may lose much of its value within a few years, while buildings and infrastructure depreciate over decades.

Depreciation is an economic cost, not merely an accounting convention. It reflects the resources that must be devoted to replacing worn-out capital rather than to expanding the capital stock. In the national accounts, '''net investment''' equals gross investment minus depreciation; net investment is the addition to the capital stock that expands productive capacity.

== Measurement ==

Measuring depreciation is difficult because the decline in value often cannot be observed directly. Economists and statisticians use several methods. '''Straight-line depreciation''' allocates the cost evenly over an assumed useful life. '''Declining-balance''' methods front-load depreciation. '''Perpetual inventory method''' builds up estimates of the capital stock from historical investment flows, assuming asset-specific service lives and depreciation patterns. The choice of method affects measured capital stock, net investment, and net domestic product.

Statistical agencies publish estimates of consumption of fixed capital as part of national accounts, and international standards such as the System of National Accounts provide guidelines. Differences in assumed asset lives and depreciation profiles can cause cross-country comparability issues.

== Economic significance ==

Depreciation matters for growth and productivity. To maintain a given capital stock, an economy must invest at least enough to replace depreciated capital. High depreciation rates, characteristic of economies with large stocks of short-lived equipment, imply higher required investment to sustain growth. The net capital stock, rather than the gross stock, is the relevant measure of productive capacity.

In growth accounting, output growth is decomposed into contributions from labour, capital, and total factor productivity. Because only net investment adds to the capital stock, depreciation reduces the contribution of investment to growth. Depreciation also affects the measurement of saving: gross saving minus depreciation yields net saving, a better indicator of the resources available for adding to the stock of wealth.

For firms, depreciation affects profit measurement and tax liabilities, since tax codes typically allow depreciation allowances that reduce taxable income. The design of these allowances influences investment incentives, and accelerated depreciation is sometimes used as a stimulus tool.

== Policy relevance ==

Depreciation influences investment and growth policy. Economies that underinvest in replacement will see their capital stock age and productivity suffer. Public infrastructure, which is often long-lived but subject to deferred maintenance, can accumulate a "depreciation backlog" that constrains growth if not addressed. Conversely, economies undergoing rapid technological change face high obsolescence of capital, which can raise depreciation and require higher gross investment to maintain competitiveness.

Environmental and resource economics extend the concept to natural capital, where depletion of forests, fisheries, and mineral deposits represents a form of depreciation that conventional accounts may not capture, motivating "green" or comprehensive wealth accounting.

== Depreciation, investment and growth ==

Depreciation shapes the relationship between investment and growth. Because only net investment adds to the capital stock, an economy must invest enough to cover depreciation before it can expand capacity. Countries with high depreciation rates, often those with capital-intensive or rapidly obsolescing industries, require higher gross investment to achieve a given growth rate. This is one reason why investment rates and growth rates do not map one-to-one across countries.

The composition of investment matters as well. Investment in short-lived assets such as software and machinery depreciates quickly, while investment in structures and infrastructure depreciates slowly. A shift in the composition of investment toward intangible assets, which has occurred in many advanced economies, can raise the effective depreciation rate and complicate the measurement of capital.

== Maintenance and the capital stock ==

Maintenance expenditure is a form of investment that offsets depreciation. Deferred maintenance allows measured net investment to appear higher in the short run but reduces the productive capacity of the capital stock over time. Public infrastructure is particularly vulnerable to deferred maintenance, and the resulting deterioration can impose costs on users and slow growth. Some analysts treat the maintenance backlog as a hidden liability, analogous to unfunded pension obligations.

Statistical treatment of maintenance varies, and the boundary between maintenance and new investment is not always clear. Repairs that restore an asset to its previous condition are maintenance; upgrades that improve it are investment. This distinction affects the measurement of depreciation and of net capital formation.

== Accounting and tax ==

In accounting, depreciation allocates the cost of an asset over its useful life, affecting reported profits and balance-sheet values. In tax systems, depreciation allowances reduce taxable income and influence investment incentives. Accelerated depreciation, which permits larger deductions in early years, raises the after-tax return to investment and is often used as a policy tool to stimulate capital spending.

The design of depreciation allowances interacts with inflation and with the cost of capital. When inflation is high, historical cost depreciation understates the replacement cost of capital, raising the effective tax burden on investment. Indexation or accelerated allowances can offset this effect.

== See also ==

* [[Capital Goods]]
* [[Gross Fixed Capital Formation]]
* [[Investment]]
* [[Capital Stock]]
* [[Economic Growth]]

== References ==


<ref name="r1">United Nations, ''System of National Accounts''.</ref>
<ref name="r2">OECD, ''Measuring Capital'' manual.</ref>
<ref name="r3">National accounts publications of statistical agencies.</ref>
<ref name="r4">World Bank research on capital accumulation and growth.</ref>

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