Step 1: Gross Domestic Product

What GDP actually measures

Picture a town with one wheat farm, one flour mill and one bakery. Wheat goes to the mill, flour goes to the bakery, and bread goes to you. How much did the town produce? If you added every sale, you would count the wheat three times, because it is hidden inside the flour and then the bread. The honest answer is the value of the bread.

That is the idea behind Gross Domestic Product. Macroeconomics looks at the whole economy, and its first question is: how big is it, and is it growing? GDP is the answer.

Examiners test every word:

1. Market value. You cannot add 3 cars to 500 haircuts, but you can add their money values.
2. Final goods. Only goods sold to the final user count. Intermediate goods (inputs such as the flour, or the steel in a car) are left out to avoid double counting.
3. Produced. Only current production counts. Selling an old house adds nothing, although the estate agent’s fee does.
4. Within a country’s borders. A Japanese-owned car factory in the UK adds to UK GDP; a British citizen working in Dubai does not.
5. In a given time period. GDP is a flow, like your income, not a stock, like your savings.

Three ways to measure the same total

In the simplest economy, households sell the factors of production (labour, land, capital and enterprise) to firms, and firms sell goods and services back to households. Money flows one way round this circular flow of income; goods and factors flow the other.

Every pound a firm receives is paid out as wages, rent or interest, or kept as profit, which is the owners’ income. So the value of what is produced equals the income earned making it, which equals the spending on it. That gives three equivalent methods:

• Output approach: add up the value added by every firm.
• Income approach: add up wages, rent, interest and profit (then add indirect taxes and subtract subsidies to move from factor cost to market prices).
• Expenditure approach: add up all spending on final goods and services. This is the one you must be able to calculate.

The expenditure approach: C + I + G + (X − M)

This equation is the backbone of macroeconomics. It splits spending on a country’s output into four parts.

\( (X – M) \) is net exports. If it is positive the country has a trade surplus; if negative, a trade deficit, which subtracts from GDP.

Nominal GDP, real GDP and the GDP deflator

Suppose a café sells 1,000 coffees this year and 1,000 last year, but the price has doubled. Its sales in money have doubled, yet it has not made a single extra coffee. A whole country has the same problem, so economists separate two measures:

• Nominal GDP is GDP at current prices. It rises when output rises, when prices rise, or both.
• Real GDP is GDP at constant base-year prices. It rises only when physical output rises.

Economic growth is the percentage change in real GDP. GDP per capita is real GDP divided by population.

GDP, GNI and comparing countries

GDP is about where production happens. Gross National Income (GNI), formerly called GNP, is about who earns the income, wherever they earn it.

The gap can be large. Ireland’s GDP is inflated by the profits of multinationals based there for tax reasons; its GNI is roughly 30% lower. In 2015 its recorded growth was revised to 26.3% while employment rose only 2.6%, an episode Paul Krugman called “leprechaun economics”. The Philippines is the opposite: GNI is above GDP because Filipinos working abroad send money home.

To compare living standards between countries, divide by population to get GDP per capita, then adjust for purchasing power parity (PPP), which allows for differences in the cost of living. A dollar buys far more in Mumbai than in Manhattan.

What GDP misses

GDP was never designed to measure welfare; its creator, Simon Kuznets, warned about exactly this. It leaves out or mismeasures:

• Unpaid work such as childcare and housework involves no market sale.
• The informal economy (cash-in-hand jobs, subsistence farming) goes largely unrecorded.
• The environment. Timber from a felled rainforest counts as output, with nothing deducted for the lost forest.
• Distribution. GDP per capita is an average, and averages hide inequality.
• Quality and new goods, such as better smartphones, are undercounted.
• Wider wellbeing: leisure, health and freedom do not appear. A country could raise GDP by abolishing weekends.

None of this makes GDP useless. It is measured consistently and tracks life expectancy and literacy closely. Use it alongside other measures, such as the UN Human Development Index, which combines income with life expectancy and education.

Practise: 6 questions

Try each one on paper first, then check the worked answer.

Check yourself

The short version

• GDP counts only final goods and services produced within a country in a period.
• Output, income and expenditure give the same total. \( \text{GDP} = C + I + G + (X – M) \), excluding transfers and share purchases.
• Real GDP = nominal GDP ÷ deflator × 100. Growth is the percentage change in real GDP; GDP per capita is real GDP ÷ population.
• GNI = GDP + net factor income from abroad. Use PPP when comparing countries.
• GDP misses unpaid work, the informal economy, environmental damage, inequality and quality changes. It measures market output, not welfare.

This guide covers the core of Chapter 19 of Economics Made Simple. For the full chapter, including the circular-flow diagram, the Ireland case study and 15 exam-style questions with a complete answer key, get the book.