Editing Stock and flow (section)

{{Short description|Types of quantities in financial fields}}
[[File:Stocks and Flows.svg|thumb|280px|Stock vs. flow]]
[[File:StockFlow.gif|thumb|246px|Dynamic stock and flow diagram]][[Economics]], business, [[accounting]], and related fields often distinguish between quantities that are '''stocks''' and those that are '''flows'''. These differ in their [[units of measurement]]. A ''stock'' is measured at one specific time, and represents a quantity existing at that point in time (say, December 31, 2004), which may have [[capital accumulation|accumulated]] in the past. A ''flow'' variable is measured over an interval of time. Therefore, a flow would be measured ''per unit of time'' (say a year). Flow is roughly analogous to [[Rate (mathematics)|rate]] or [[speed]] in this sense.

For example, U.S. nominal [[gross domestic product]] refers to a total number of dollars spent over a time period, such as a year. Therefore, it is a flow variable, and has units of dollars/year. In contrast, the U.S. nominal [[Capital (economics)|capital stock]] is the total value, in dollars, of equipment, buildings, and other real productive assets in the U.S. economy, and has units of dollars. The diagram provides an intuitive illustration of how the ''stock'' of [[Capital (economics)|capital]] currently available is increased by the ''flow'' of new [[investment (macroeconomics)|investment]] and depleted by the ''flow'' of [[depreciation]].