How is a currency's value determined, and how does a change in it affect trade and the economy?
Explain how exchange rates are determined and analyse how a change in the exchange rate affects the balance of payments and the economy
A focused answer to the H2 Economics learning outcome on exchange rates. How the demand for and supply of a currency set its value, the effects of appreciation and depreciation on the balance of payments, inflation and growth, and the Marshall-Lerner condition.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
SEAB wants you to explain how exchange rates are determined and analyse how a change in the exchange rate affects the balance of payments and the economy. The central insight is that a currency's value is a price set by supply and demand, and that a change in it has opposing effects - on competitiveness and growth versus inflation - whose net result depends on elasticities and time.
The answer
How a floating exchange rate is determined
In a floating system, the exchange rate is the price of one currency in terms of another, set by demand for and supply of the currency in the foreign-exchange market:
- Demand for the currency comes from foreigners who need it to buy the country's exports and to invest in the country.
- Supply of the currency comes from residents who need foreign currency to buy imports and to invest abroad.
The rate settles where demand equals supply. Anything that raises demand (stronger exports, higher inflows) appreciates the currency; anything that raises supply (more imports, outflows) depreciates it.
Exchange-rate systems range from freely floating (market-determined) through managed float (the central bank influences it, as Singapore does) to a fixed peg.
Appreciation and depreciation
- Appreciation (a stronger currency): exports become dearer to foreigners, imports cheaper at home. This tends to worsen the current account but lowers imported inflation.
- Depreciation (a weaker currency): exports become cheaper to foreigners, imports dearer at home. This tends to improve the current account and raise AD, output and employment, but raises imported inflation.
The Marshall-Lerner condition and the J-curve
A depreciation does not automatically improve the current account; two qualifications matter:
So the short-run and long-run effects of a depreciation differ, and the outcome depends on how responsive export and import demand are.
Effects on the wider economy
Beyond the current account, a depreciation raises AD (via net exports), supporting output and employment, but adds to inflation through dearer imports. An appreciation does the reverse. This is why the exchange rate is such a powerful macroeconomic lever for an open economy and why it is used as Singapore's main monetary instrument.
Examples in context
Example 1. Singapore's managed exchange rate. Because Singapore manages its dollar against a trade-weighted basket, it deliberately uses the appreciation-inflation and depreciation-competitiveness trade-off: appreciating to curb imported inflation and easing the appreciation to support exports in a downturn. Its policy is a direct application of how exchange-rate changes affect inflation, the current account and growth.
Example 2. A depreciation and the J-curve in a trade-dependent economy. When a country's currency falls sharply, its trade balance often worsens for several months (the J-curve) before improving as exporters win new orders and importers switch away from dearer foreign goods. The episode shows why policymakers judge a depreciation over time and against the Marshall-Lerner condition rather than expecting an instant improvement.
Try this
Q1. Explain what causes a currency to appreciate in a floating system. [2 marks]
- Cue. A rise in demand for the currency (from stronger exports or capital inflows) relative to its supply bids up its price, appreciating it.
Q2. Explain the main trade-off of a depreciation. [3 marks]
- Cue. It makes exports cheaper and imports dearer, improving competitiveness and net exports and raising AD and output, but dearer imports raise the price level, causing imported inflation, so competitiveness is gained at the cost of higher inflation.
Q3. State the Marshall-Lerner condition. [2 marks]
- Cue. A depreciation improves the current account only if the sum of the price elasticities of demand for exports and imports is greater than one.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original10 marksExplain how the exchange rate of a freely floating currency is determined, and analyse the effects of a depreciation on the economy.Show worked answer →
A 10 mark question rewards the demand-supply determination and the effects of a depreciation.
Determination. In a floating system, the exchange rate is set by the demand for and supply of the currency in the foreign-exchange market. Demand comes from foreigners buying exports and investing in the country; supply comes from residents buying imports and investing abroad. The rate settles where demand equals supply, and shifts in either move it.
Depreciation effects. A weaker currency makes exports cheaper to foreigners and imports dearer at home. Exports tend to rise and imports to fall, improving the current account (subject to the Marshall-Lerner condition) and raising AD, output and employment. But dearer imports raise the price level: imported inflation. So a depreciation boosts competitiveness and growth at the cost of higher inflation.
Markers reward the demand-supply determination, the cheaper-exports-dearer-imports mechanism, the current-account and AD effects, and the imported-inflation cost.
Original9 marksExplain the Marshall-Lerner condition and the J-curve effect, and why they matter for a depreciation.Show worked answer →
A 9 mark question rewards both concepts and their link to elasticities and time.
- Marshall-Lerner condition
- A depreciation improves the current account only if the sum of the price elasticities of demand for exports and imports is greater than one. If demand is too inelastic, the higher volume of exports and lower volume of imports do not offset the worse prices, and the current account can worsen.
- J-curve
- In the short run, demand for exports and imports is inelastic (contracts and habits take time to adjust), so a depreciation may first worsen the current account before improving it as volumes respond. Plotted over time, the current account traces a J shape.
- Why it matters
- A depreciation is not guaranteed to improve the current account: it depends on elasticities (Marshall-Lerner) and takes time (J-curve), so the short-run and long-run effects differ.
Markers reward the elasticity-sum condition, the short-run inelasticity behind the J-curve, and the conclusion that the effect depends on elasticities and time.
Related dot points
- Explain comparative advantage and use it to show how specialisation and trade raise total output
A focused answer to the H2 Economics learning outcome on comparative advantage. The difference from absolute advantage, how opportunity cost determines who should specialise, and how trade within the terms-of-trade range raises total output.
- Evaluate the case for free trade, and explain trade creation and trade diversion under trade agreements
A focused answer to the H2 Economics learning outcome on free trade. The benefits of free trade from specialisation, competition and scale, the meaning of trade creation and trade diversion in trade blocs, and the case against unrestricted trade.
- Analyse the methods and effects of protectionism using a tariff diagram, and evaluate the arguments for and against it
A focused answer to the H2 Economics learning outcome on protectionism. The methods (tariffs, quotas, subsidies), the welfare effects of a tariff shown on a diagram, and a balanced evaluation of the arguments for and against protection.
- Explain the causes of globalisation and evaluate its economic effects on growth, inequality and development
A focused answer to the H2 Economics learning outcome on globalisation. The drivers of growing world integration, the benefits for growth and consumers, the costs including inequality and vulnerability, and a balanced evaluation.
- Explain the managed exchange rate as Singapore's main monetary tool, its transmission and its trade-offs
A focused answer to the H2 Economics learning outcome on exchange-rate-centred monetary policy. Why a small open economy manages the exchange rate, how a stronger or weaker currency affects inflation and net exports, and the trade-offs involved.