Tags: exchange rate, floating exchange rate, fixed exchange rate, managed float, devaluation, revaluation, depreciation, appreciation, J-curve, Marshall-Lerner condition, real effective exchange rate, A2 economics
Difficulty: Intermediate | Prerequisites: AS Economics Chapters 8–10 (floating exchange rate basics, trade fundamentals), plus the BoP study notes from this chapter.
Exchange rates determine the price at which one currency trades for another, and they affect everything from the cost of imports to the competitiveness of exports, the rate of inflation, and the flow of international investment. This section of Chapter 15 builds on the floating exchange rate material from AS and extends it to cover fixed and managed float systems, the mechanics of central bank intervention, and the short-run versus long-run consequences of currency movements. You need to understand how exchange rate changes ripple through the current account, aggregate demand, GDP, and inflation, and why the J-curve and the Marshall-Lerner condition matter for evaluating devaluation as a policy tool.
Exchange rates can be floating (set by markets), fixed (set by government), or managed float (market-determined within limits). Currency depreciation makes exports cheaper and imports dearer, but only improves the current account in the long run once demand adjusts (the J-curve). The Marshall-Lerner condition states that devaluation improves the current account only if the combined price elasticities of demand for exports and imports exceed one.
Nominal exchange rate (NER)
The price of one currency in terms of another. For example, 1 USD = 7 Chinese yuan.
Trade-weighted exchange rate
An index measure of a currency's value against a basket of other currencies, where each currency is weighted by its importance in that country's trade. Think of it as a weighted average of how strong or weak your currency is against all your main trading partners.
Real effective exchange rate (REER)
Nominal exchange rate multiplied by (domestic CPI / foreign CPI). This adjusts for inflation differences and measures how many domestic goods can be exchanged for foreign goods. In simple terms, it tells you the actual purchasing power of your currency abroad, not just the headline rate.
Floating exchange rate
A system where the currency's value is determined entirely by market forces of demand and supply, with no government intervention.
Fixed exchange rate
A system where the government or central bank sets and maintains a specific exchange rate, known as the official exchange rate (OER).
Managed float (dirty float)
A hybrid system combining elements of floating and fixed rates. The currency floats within upper and lower limits set by the central bank, which intervenes only when the rate moves beyond those bounds.
Appreciation
A rise in the value of a currency under a floating exchange rate system, driven by market forces.
Depreciation
A fall in the value of a currency under a floating exchange rate system, driven by market forces.
Revaluation
A deliberate increase in the value of a currency by the government under a fixed exchange rate system. Think of it as the government making its currency more expensive on purpose.
Devaluation
A deliberate decrease in the value of a currency by the government under a fixed exchange rate system. The government makes its currency cheaper to boost export competitiveness.
J-curve
The pattern showing that after a depreciation, the current account initially worsens (because demand is inelastic in the short run) before improving in the long run (once demand becomes elastic). The shape of the time path looks like the letter J.
Inverse J-curve
The opposite pattern after an appreciation: the current account initially improves (inelastic demand in the short run) before worsening in the long run.
Marshall-Lerner condition
The current account will improve following a depreciation only if PED of exports + PED of imports > 1. This condition is typically met in the long run but not in the short run.
The straightforward price of one currency in terms of another. If 1 USD = 7 yuan, that is the nominal exchange rate.
An index that measures a currency's value against a basket of currencies. Each currency in the basket is assigned a weight based on its share of the country's trade. A rise in the trade-weighted index means the currency has strengthened on average against its trading partners.
Formula:
\text{REER} = \text{NER} \times \frac{\text{Domestic CPI}}{\text{Foreign CPI}}This adjusts the nominal rate for relative price levels, giving a more accurate picture of international competitiveness.
Worked example: The NER of the Chinese yuan to the US dollar is 7 yuan per dollar. US CPI (domestic) is 100, China CPI (foreign) is 150. So REER = 7 x (100/150) = 4.7. This means on average 1 US good can be exchanged for 4.7 Chinese goods.
The exchange rate is set entirely by market forces of demand and supply. The central bank does not intervene. Covered in detail at AS level.
Advantages:
The exchange rate automatically adjusts, moving the current account towards equilibrium and eliminating persistent deficits or surpluses.
No need for the central bank to hold foreign exchange reserves, freeing those resources for other uses.
The government can pursue other objectives more freely (e.g. setting interest rates to target inflation rather than to defend the exchange rate).
Disadvantages:
Currency instability may discourage international trade and investment.
Speculation can cause volatile movements in the exchange rate, contributing to current account swings.
Depreciating pressure on the currency can cause imported inflation.
The government or central bank sets and maintains a fixed rate (the official exchange rate, OER). The central bank has two main tools to hold the rate:
1. Buying and selling foreign exchange reserves:
If there is appreciating pressure (demand for the currency rises or supply falls), the central bank sells local currency and buys foreign reserves, increasing the supply of local currency back to the fixed rate.
If there is depreciating pressure (demand falls or supply rises), the central bank buys local currency using its foreign reserves, increasing demand for the local currency back to the OER.
2. Adjusting interest rates:
To counter appreciating pressure, the central bank can lower interest rates (reducing demand for the currency from foreign investors).
To counter depreciating pressure, the central bank can raise interest rates (attracting foreign capital and increasing demand for the currency).
Advantages:
Greater certainty and stability for trade and investment, reducing exchange rate risk.
Less speculative activity, and a more stable debt burden, particularly if there is depreciating pressure.
Reduces imported inflation that would result from a depreciating currency (especially important for developing countries).
Keeps external debt burden in check.
Disadvantages:
The central bank must hold large reserves to intervene, which carries an opportunity cost.
The rate may not be set at the right level: too high discourages exports, too low increases import prices and causes inflation.
Policies to defend the fixed rate (e.g. raising interest rates) may conflict with domestic objectives such as growth and employment.
Revaluation is when the government deliberately increases the value of the currency under a fixed system. It is done by selling foreign reserves (increasing demand for local currency) or raising interest rates. The purpose is to make imports cheaper or reduce external debt burden. Countries like Pakistan, experiencing depreciating pressure, sometimes artificially overvalue their currency for these reasons. Consequences mirror those of appreciation.
Devaluation is when the government deliberately decreases the value of the currency. It is done by buying foreign reserves (increasing supply of local currency) or lowering interest rates. The purpose is to make exports cheaper, boost export revenue, improve GDP and employment, and strengthen local industry competitiveness. Countries like China, experiencing appreciating pressure, have historically undervalued their currency. Consequences mirror those of depreciation.
A combination of floating and fixed approaches, often used by developing countries. The central bank sets an upper and lower limit for the exchange rate. Within those limits, the currency floats freely. If the rate breaches either limit, the central bank intervenes using the same two tools as in a fixed system (reserves and interest rates). In some cases, only a lower limit is set when a country faces persistent depreciating pressure.
When the exchange rate falls (ER↓), export prices fall (P_X↓) and import prices rise (P_M↑). This makes exports more attractive to foreign buyers and imports less attractive to domestic consumers.
Short run (demand is inelastic):
Export prices fall significantly, but demand rises only slightly (inelastic), so export revenue decreases.
Import prices rise significantly, but demand falls only slightly, so import expenditure increases.
The current account deficit worsens.
Aggregate demand falls (because net exports worsen).
GDP, incomes, and employment fall.
Demand-pull inflation falls, but cost-push inflation rises (imported raw materials cost more).
Long run (demand becomes elastic):
Export prices fall by less, but demand rises by a lot (elastic), so export revenue increases.
Import prices rise by less, but demand falls by a lot, so import expenditure decreases.
The current account improves.
Aggregate demand rises.
GDP, incomes, and employment rise.
Demand-pull inflation rises, cost-push inflation remains high.
Conclusion: exchange rate depreciation is harmful in the short run but beneficial in the long run.
The J-curve illustrates the time path of the current account after a depreciation. Immediately after the depreciation, the current account worsens (moving further into deficit) because demand is inelastic in the short run. Over time, as consumers and firms adjust to the new prices, demand becomes elastic, and the current account begins to improve, eventually moving into surplus. The shape of this path resembles the letter J.
Short run (demand is inelastic):
Export prices rise significantly, but demand falls only slightly, so export revenue increases.
Import prices fall significantly, but demand rises only slightly, so import expenditure decreases.
The current account improves.
Aggregate demand rises.
GDP, incomes, and employment rise.
Demand-pull inflation rises, cost-push inflation falls.
Long run (demand becomes elastic):
Export prices rise by less, but demand falls by a lot, so export revenue decreases.
Import prices fall by less, but demand rises by a lot, so import expenditure increases.
The current account worsens.
Aggregate demand falls.
GDP, incomes, and employment fall.
Demand-pull inflation falls, cost-push inflation remains low.
Conclusion: exchange rate appreciation is beneficial in the short run but harmful in the long run.
The mirror image of the J-curve. After an appreciation, the current account initially improves (inelastic demand, short run) before worsening in the long run as demand becomes elastic.
Devaluation or depreciation will improve the current account only if:
\text{PED}_X + \text{PED}_M > 1If the combined price elasticity of demand for exports and imports exceeds 1, the volume effect outweighs the price effect, and the current account improves. This condition is almost always met in the long run, but rarely in the short run, which is why the J-curve pattern occurs.
The quantities of exports and imports (Q_X, Q_M) measure volume. Export revenue (X_R) and import expenditure (M_E) measure value. The current account depends on value, not volume. This is why the elasticity of demand matters so much: even if the volume of exports rises after a depreciation, revenue may fall if the price drop outweighs the quantity gain.
Students confuse depreciation (market-driven, floating system) with devaluation (government-driven, fixed system). The terms are not interchangeable. Appreciation and revaluation are the corresponding upward pairs.
Students often think that depreciation immediately improves the current account. It does not. The J-curve shows that the current account initially worsens before improving.
A common error is forgetting that the current account depends on the value (revenue and expenditure), not the volume (quantities) of trade. A rise in export volume does not guarantee a rise in export revenue if prices have fallen.
Students sometimes assume that the Marshall-Lerner condition is always met. It is typically met in the long run but not in the short run, which is exactly why the J-curve pattern exists.
⚠️ The J-curve and the Marshall-Lerner condition are among the most frequently tested topics in A2 economics. Be ready to draw the J-curve diagram and explain its shape using short-run inelastic and long-run elastic demand.
⚠️ Comparison questions on exchange rate systems (floating vs fixed vs managed float) are common. Know the pros and cons of each and be able to evaluate which system suits different types of economies.
⚠️ Examiners reward students who distinguish between short-run and long-run consequences of exchange rate changes. Always structure your analysis around this distinction.
⚠️ The REER formula may appear in calculation questions. Practise the arithmetic and understand what the result means in terms of real purchasing power.
True or false: Depreciation and devaluation mean the same thing. (False: depreciation is market-driven under a floating system; devaluation is government-driven under a fixed system.)
Fill in the blank: The Marshall-Lerner condition states that PED_X + PED_M must be greater than ______ for devaluation to improve the current account. (1.)
True or false: After a depreciation, the current account immediately improves. (False: the J-curve shows it initially worsens.)
Fill in the blank: In a managed float system, the central bank sets ______ and ______ limits for the exchange rate. (Upper and lower.)
True or false: The real effective exchange rate adjusts for differences in price levels between countries. (True.)
Q: Explain the difference between a floating and a fixed exchange rate system.
A: In a floating system, the exchange rate is determined by market demand and supply with no government intervention. In a fixed system, the government or central bank sets an official rate and intervenes to maintain it, using foreign exchange reserves and interest rate adjustments. A floating system adjusts automatically but can be volatile; a fixed system provides stability but requires reserves and may conflict with other policy objectives.
Q: Using the J-curve, explain why a depreciation initially worsens the current account before improving it.
A: Immediately after depreciation, export prices fall and import prices rise. However, in the short run, demand for both exports and imports is price-inelastic because consumers and firms have existing contracts and habits. Export revenue falls (price drops, volume barely rises) and import expenditure rises (price rises, volume barely falls), so the current account worsens. Over time, demand adjusts and becomes elastic: export volumes rise substantially and import volumes fall substantially. Revenue effects reverse and the current account improves. The time path of this adjustment traces the shape of the letter J.
Q: Evaluate the use of devaluation as a policy to correct a current account deficit.
A: Devaluation makes exports cheaper and imports more expensive, which should improve the current account. However, this only works if the Marshall-Lerner condition is satisfied (PED_X + PED_M > 1), which is usually the case in the long run but not in the short run. In the short run, the J-curve effect means the deficit initially worsens. There must be no retaliation from trading partners, inflation must be kept low to preserve the price advantage, and domestic industries must have spare capacity to increase output. It is a useful tool but not a quick fix.
Q: Compare the advantages and disadvantages of a fixed exchange rate system.
A: Advantages include greater certainty for trade and investment, reduced speculation, lower imported inflation (especially for developing countries facing depreciation pressure), and a stable external debt burden. Disadvantages include the opportunity cost of holding reserves, the risk of setting the rate at an inappropriate level (too high harms exports, too low causes inflation), and the conflict between defending the rate and pursuing domestic objectives like growth and employment.
This material connects directly to the BoP study notes (same chapter), since exchange rate policy is one of the main tools for correcting a current account deficit. The floating ER foundations come from AS Chapters 8–10. The aggregate demand model from earlier in the course is essential for understanding how exchange rate changes feed through to GDP, employment, and inflation. The Marshall-Lerner condition and J-curve also link to price elasticity of demand (a microeconomic concept applied in a macroeconomic context).
Exchange rate, nominal exchange rate, NER, trade-weighted exchange rate, real effective exchange rate, REER, floating exchange rate, fixed exchange rate, managed float, dirty float, appreciation, depreciation, revaluation, devaluation, J-curve, inverse J-curve, Marshall-Lerner condition, PED exports, PED imports, central bank intervention, foreign exchange reserves, official exchange rate, OER, currency devaluation China, currency overvaluation Pakistan, A2 economics, macroeconomics, CIE economics, Cambridge economics, international trade