How Are GDP and GNI Measured?
Measuring economic activity
What you will learn
- GDP measures production within a country; GNI adjusts it for residents' net income from abroad.
- Reconcile expenditure, income and output approaches
Essential definitions
- GDP
- The monetary value of final goods and services produced within an economy during a period.
- GNI
- GDP plus net primary income received from abroad.
- Value added
- The value of output minus the value of intermediate inputs purchased from other producers.
Count production once
Gross domestic product, GDP, is the value of final goods and services produced inside an economy during a period. Final means bought for use rather than further production. Flour bought by a bakery is an intermediate input; flour bought by a household is a final purchase.
Suppose grain sells for 2, flour for 3 and the finished bread for 5 currency units. Adding all sales gives 10 and counts the grain repeatedly. Instead, add value added: 2 by the farmer, 1 by the mill and 2 by the baker. The total is 5, equal to the final bread price. A second-hand sale adds no new bread or house to production, although a newly supplied dealer's service counts.
Three ways to measure the same activity
The output approach adds value added. The income approach adds incomes earned in production, with adjustments to make valuation consistent. The expenditure approach adds spending on final domestic output. These totals should agree in principle; measurement errors create discrepancies. Do not add the three estimates together.
The expenditure formula is GDP = C + I + G + X − M. C is household consumption, I investment in new capital and inventories, G government purchases, X exports and M imports. Measure each in the same currency and period. Subtract imports because imported purchases may already be included in C, I or G but were produced abroad. Transfers and purchases of existing financial assets are not purchases of new output.
From domestic production to residents' income
Gross national income, GNI, follows residents' income rather than the location of production. Net primary income from abroad is residents' income earned abroad minus income paid to non-residents. GNI = GDP + net primary income from abroad.
A foreign-owned bakery's local output belongs in domestic GDP. Profit paid to its overseas owner is an outward income payment, lowering GNI relative to GDP. Residents' income from assets abroad works in the opposite direction. The calculation below uses annual billions throughout. Neither total reveals how income is shared; later lessons make that limitation explicit.
Hypothetical national accounts
- C = 400, I = 90, G = 120, X = 80 and M = 100 billion currency units.
- GDP = 400 + 90 + 120 + 80 − 100 = 590 billion.
- Primary income received from abroad = 25; paid abroad = 40. Net primary income = −15 billion.
GNI = 590 − 15 = 575 billion currency units.
Circular flow: income, spending and leakages
S goes to the financial sector, T to government and M to overseas producers. I buys capital goods, G buys domestic output, and X is overseas spending on domestic exports. Equilibrium requires total S + T + M = I + G + X, not equality of each pair. Planned injections above leakages tend to expand activity; the reverse tends to contract it, subject to capacity and price adjustment. Real flows for the three outside sectors are omitted for clarity.
Firms buy factors from households and sell final output back to them. Income finances expenditure. Saving, taxes and imports divert spending; investment, government purchases and exports inject spending into domestic firms.
How to draw it and model assumptions
- Place households and firms opposite each other.
- Use opposite arrows for real resources/output and money payments.
- Connect financial, government and overseas sectors. Label S, T, M leakages and I, G, X injections.
Flows are measured over the same period. In the simple equilibrium, planned S + T + M equals planned I + G + X. Transfers redistribute income and are not government purchases of new output.
Apply and evaluate
- Informal activity and imperfect records create measurement difficulties.
- GDP is useful for domestic productive activity; GNI can better describe income available to residents, but neither is a distribution measure.
Common misconceptions
- Government transfers are not government purchases in GDP.
- A purchase of an existing financial asset is not current capital formation.
Knowledge check
Why subtract imports in the expenditure approach?
Real-world application
A GDP estimate has a publication vintage
12 February 2021: The UK Office for National Statistics initially reported a 9.9% annual GDP fall for 2020. This is the estimate in that release, not a claim about the latest revised series.
Use this historical release to distinguish real output from its statistical estimate. Later revisions can change the measured size of a recession without changing what households experienced at the time. For a cross-country comparison, use consistent years, definitions and data vintages.
ONS, GDP monthly estimate, UK: December 2020 ↗Historical evidence checked 9 October 2026. The model interpretation is an original teaching application.
What to remember
GDP measures production within a country; GNI adjusts it for residents' net income from abroad. Output, income and expenditure are three views of the same activity.
Completion is your own reflection on learning, not a test score. Syllabus references: 3.1.02, 3.1.03, 3.1.04.
Lessons in this section
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