Direct answer
A worked example of GDP shows how you turn a set of economic quantities into one number. One common approach calculates GDP using the spending identity: GDP = C + I + G + (X − M), where C is household consumption, I is investment (often interpreted as spending on new capital or inventory changes), G is government spending, X is exports, and M is imports. This example uses a hypothetical economy and states every assumption so the arithmetic can be verified.
Mechanism: what GDP calculation is doing
GDP (Gross Domestic Product) is a measure of economic activity within a country’s borders over a period of time. In the spending approach, it does not ask whether goods are “needed” or whether the economy is “healthy”; it totals spending components that correspond to domestic production.
Key definitions for the worked example (simplified):
- Household consumption (C): spending by households on goods and services.
- Investment (I): spending that adds to the capital stock or covers inventory changes (for simplicity here, we treat it as “spending on new capital and inventories”).
- Government spending (G): spending by the government on goods and services.
- Net exports (X − M): exports minus imports.
Worked example (fully numerical with stated assumptions)
Assumptions for this scenario:
- Time period: one year (or an equivalent period).
- All amounts are measured in the same currency and at the same price basis (so they can be added).
- The economy contains no statistical adjustments beyond those four components.
- We treat all “investment” as already belonging in the I category (no reclassification between C and I).
Hypothetical inputs:
- C (household consumption) = 500
- I (investment) = 120
- G (government spending) = 80
- X (exports) = 90
- M (imports) = 110
Step-by-step calculation:
- Compute net exports: X − M = 90 − 110 = −20.
- Add the spending components: GDP = C + I + G + (X − M).
- Substitute values: GDP = 500 + 120 + 80 + (−20).
- Sum: GDP = 680.
Interpretation strictly within the identity:
- The result 680 means total domestic spending components, as defined, sum to 680 under the assumptions.
- The negative net exports term (−20) indicates that imports exceed exports in this scenario, pulling down GDP via the identity.
Limitations and failure modes (what can go wrong)
Material limitations mean you can compute the identity correctly and still get a number that is incomplete or misleading.
- Measurement boundaries: GDP counts market transactions, but some valuable activity may be outside those measurements (for example, unpaid household work or informal production). The spending identity still holds within what is measured.
- Classification and double counting risks: If a transaction is misclassified (for instance, treated as consumption instead of investment), GDP can be distorted even though the arithmetic is correct.
- Price and timing issues: If components are measured using inconsistent price bases or occur in different periods, adding them can be invalid. The worked example avoided this by assumption.
- No guarantee of future outcomes: A GDP level or growth rate can be computed without implying that the economy will improve or worsen.
Verification: how to independently check the example
To verify independently, focus on arithmetic and definitions:
- Check the identity used: GDP = C + I + G + (X − M).
- Recalculate X − M first.
- Add C + I + G + (X − M) using the same assumptions.
- Confirm that each component is defined consistently (especially investment and the treatment of imports/exports).
A next question you may ask is how GDP changes when definitions shift—such as using real versus nominal measures or choosing different price bases—because the identity can be applied, but the inputs must match.