Stocks and flows

Capital stock means the quantity or value of capital assets available at a particular moment, such as the value of machines on 31 March. It is not measured over a period. Therefore, capital stock is measured at a point of time, whereas investment and production are measured during a period.

Capital formation is the addition to the stock of capital during a specified period. It includes investment in machinery, buildings, and other productive assets over a month, year, or another interval. Since it records a change occurring through time, capital formation is a flow variable, not a stock.

Depreciation is the loss in value or productive capacity of a capital asset during a period because of wear, use, or obsolescence. It is calculated for a month, year, or other interval. Thus depreciation is a flow variable, while the remaining value of the asset at a date is a stock.

The value of a machine on a particular day is measured at a specific point in time, not over a period. Therefore, it is a stock variable. Stocks include the value of assets, wealth, capital, or inventories existing at a given date, whereas flows are measured per day, month, or year.

Daily production is measured over a period of time, namely one day. Therefore, it is a flow variable. A flow records the quantity produced, earned, spent, or received during a specified period, whereas a stock records a quantity at a particular point in time. Thus, factory production per day is a flow.

Finished goods kept in a warehouse represent the quantity available at a specified moment. They are accumulated inventory existing at that time, regardless of when the goods were produced. Therefore, warehouse inventory at a given time is a stock; production and sales over a period are flows.

A monthly rent payment is measured over the whole month rather than at one particular instant. It represents an amount paid during a stated period, so it is a flow variable. Payments, income, expenditure, saving, and production are generally flows when expressed per month, per year, or for any other time interval.

A house is an asset whose value is measured at a specific point in time, such as 31 March or 1 January. Therefore, it is a stock variable. A stock records the level or quantity existing at a particular moment, whereas a flow records an amount accumulated during a period, such as monthly income or annual expenditure.

The expenditure on buying a house is recorded during a year, so it is measured over a time interval and is a flow. The house itself, or its value on a particular date, is a stock. This distinction is important: acquisition expenditure is a flow even though the asset acquired becomes part of the owner’s stock of wealth.

The governing concept is the stock-flow distinction in macroeconomics. A stock variable is measured at a particular point in time, like a snapshot, and records the amount existing at that date. A bank balance on a particular date shows the money held in the account at that exact moment, so option C is correct. Annual income, monthly consumption, and daily sales are flow variables because each is measured over a duration—one year, one month, or one day. The length of the period does not change the classification; what matters is whether the value is observed at one date or accumulated during an interval. Thus the bank balance is the only stock in the list.

Annual income is earned and measured throughout the period of one year. Since its value depends on the specified time interval, it is a flow variable. Total money, population, and wealth generally describe quantities existing at a point in time and are treated as stock variables in this comparison.

The phrase ‘per month’ specifies a time period over which the quantity is measured. A variable expressed per month is therefore generally a flow, such as monthly income, expenditure, saving, or production. A stock is instead measured at a point in time, for example wealth or a bank balance on a particular date.

A stock variable is measured at a particular point in time. The phrase “at the end of a year” identifies a specific date or moment, so it generally refers to a stock, such as wealth, inventory, or bank balance. A flow, in contrast, is measured over an interval, such as income earned throughout the year.

Income and consumption are both normally measured over a period, such as a month or a year, so both are flow variables. Population, wealth, bank balance, capital stock, and warehouse inventory are generally measured at a point in time and are stocks. Hence option B contains the only pair of flows.

Wealth and bank balance are measured as amounts existing at a particular point in time. They represent accumulated resources or balances, not activities completed during a period. Income, production, sales, investment, and consumption are generally measured over a period and are therefore flow variables.

Wealth is accumulated value measured at a point in time, so it is a stock. Annual income is earned over the period of one year, so it is a flow. Option A therefore follows the required order. The other options either reverse the order or place a flow before a stock.

Monthly saving is a flow because it is measured during one month. A bank balance is a stock because it is measured at a particular date or moment. The other pairs reverse the required order or contain two variables of the same relevant type, so option B is the only pair in which the first is a flow and the second is a stock.

Profit earned during a year is calculated over the interval from the beginning to the end of that year. It represents income generated during a period, not an accumulated balance held at one instant. Therefore annual profit is a flow variable, while retained wealth or cash balance on a date is a stock.

The total value of a company’s share capital on a particular day represents the capital existing at one specific point in time. Hence, it is a stock variable. The word “on a particular day” is important because stocks are measured at a date, whereas flows such as income, sales, or expenditure are measured over a period.

Tax collection during a financial year is measured over a period, not at one particular moment. Therefore, it is a flow variable. The total amount collected is accumulated throughout the year. In contrast, a stock, such as government cash balance or public debt, is measured at a specific date.

Cash balance at the end of a day is the amount remaining at one specified point in time. It is a stock because it records the financial position on that date, even though payments and receipts during the day are flows. The word “balance” is an important clue to the stock classification.

A cash payment made during a day is measured over the time interval of that day, so it is a flow variable. The payment records an economic transaction occurring during the period. In contrast, the company’s cash balance or cash held at the end of that day is a stock because it is measured at a particular point in time.

Total wealth today is measured at a particular point in time, making it a simple example of a stock variable. A stock shows an existing amount of assets or wealth at a date. Annual income, monthly expenditure, and daily sales are flows because each is measured over a stated period rather than at one instant.

Income of one year is measured over the complete interval of a year, so it is a flow variable. A flow records an amount earned, spent, produced, or transferred during a period. Population, bank balance, and wealth on a date are quantities existing at a point in time and are therefore stocks.

The value of crops sold during a year is calculated by adding sales made throughout that year. Since it is measured over a time interval, it is a flow variable. The crop stock or the value of unsold crops held by the farmer on a particular date would be a stock, but sales during the year are flows.