Business Economics · Balance of payments and exchange rates

Exchange Rates and the Macroeconomy: Marshall-Lerner and the J-Curve

Updated 11 October 2026 · Fact-checked

A fall in the exchange rate (depreciation) makes exports cheaper and imports dearer. The trade balance improves only if the Marshall-Lerner condition holds: the sum of the price elasticities of demand for exports and imports exceeds 1. In the short run the J-curve means the balance often worsens first. Depreciation also raises import prices and inflation.

Understand Exchange Rates and the Macroeconomy

The exchange rate is the price of one currency in terms of another. If ₹1 buys fewer dollars than before, the rupee has depreciated. If it buys more, the rupee has appreciated. Here we treat a floating rate, where market forces move the rate. A government can also choose to devalue or revalue a fixed rate, with similar effects.

Start with price effects. When the rupee depreciates, Indian goods cost less in foreign currency, so foreigners want more of them. Foreign goods cost more in rupees, so Indians want fewer of them. Exports should rise and imports should fall. This is the expenditure-switching effect.

But the trade balance is measured in money, not volume. After depreciation, each unit of imports costs more rupees. Each unit of exports earns fewer dollars. The balance improves only if volumes respond strongly enough. This is what the Marshall-Lerner condition tests: the sum of the price elasticities of demand for exports and imports (in absolute value) must be greater than 1. It is usually stated for a starting point where trade is roughly balanced.

The J-curve shows timing. In the short run, contracts are already signed and buyers cannot switch quickly, so demand is inelastic. Import bills rise in rupee terms while volumes barely change, so the current account worsens. Over months, volumes adjust, elasticities rise and the balance improves. Plotted over time, the balance dips then rises, like the letter J.

The wider macro effects matter for exams. Depreciation raises import prices, which pushes up cost-push inflation, especially if the country imports oil or inputs. Higher net exports raise aggregate demand, which can boost output and growth if there is spare capacity, and can add demand-pull inflation if not. Firms with foreign-currency debt face higher repayment costs. Appreciation does the reverse: it lowers inflation but hurts export competitiveness.

Key rules to remember

Marshall-Lerner condition: |PEDx| + |PEDm| > 1; PEDx is price elasticity of demand for exports, PEDm for imports. If the sum is above 1, depreciation improves the trade balance. If it equals 1, no change. If below 1, it worsens. Standard form assumes trade starts near balance and supply is elastic.
Exchange rate change: % change in rate = (new rate − old rate) ÷ old rate × 100; Be clear on quotation. If the rate is ₹ per $, a rise means rupee depreciation.
Elasticity: PED = % change in quantity demanded ÷ % change in price; Use absolute values when applying Marshall-Lerner.
Net exports: Net exports = X − M; Trade balance in value terms. Net exports is a component of aggregate demand: AD = C + I + G + (X − M).
Foreign-currency price of exports: Foreign price = rupee price ÷ exchange rate (₹ per unit of foreign currency); A higher ₹ per $ rate lowers the dollar price of an Indian export, if rupee price stays fixed.

How to solve Exchange Rates and the Macroeconomy questions

Use this order for any question on exchange rates and the macroeconomy. It keeps your argument logical and covers what examiners look for.

1Identify the direction: is the currency depreciating or appreciating? Check the quotation (₹ per $ or $ per ₹).
2State the immediate price effects: export prices in foreign currency, import prices in domestic currency.
3Apply elasticity: find or estimate the sum of the export and import price elasticities and compare with 1 (Marshall-Lerner).
4Add timing: say whether the question is short run or long run. In the short run, discuss the J-curve. In the long run, elasticities are higher.
5Trace the effect on aggregate demand and growth: net exports change, so AD changes. Mention spare capacity.
6Trace the effect on inflation: import prices, input costs, and demand-pull pressure.
7Note other effects if relevant: foreign-currency debt, competitiveness, supply elasticity, policy responses.
8Conclude with a judgement: the net effect depends on elasticities, time period, and the economy's structure.

Quickest way: Three-check shortcut for depreciation questions

When to use it: Use for MCQs and for planning a short written answer.

Check direction and quotation first. Wrong direction loses the whole question.
Sum the two elasticities. Above 1: balance improves. Below 1: worsens. Exactly 1: no change.
If the question says 'short run' or 'immediately', expect the balance to worsen (J-curve). If 'long run', expect improvement if the condition holds.
For inflation, depreciation is inflationary, mainly through import prices. Appreciation is disinflationary.

Common mistakes in Exchange Rates and the Macroeconomy

Saying depreciation always improves the trade balance.
Students remember that exports become cheaper and stop there.
Fix: Always test the Marshall-Lerner condition. Improvement needs the elasticity sum to exceed 1, and it is often delayed.
Using only one elasticity, such as export elasticity alone.
The condition is remembered as 'elasticity above 1'.
Fix: Add the export and import elasticities (absolute values) and compare the sum with 1.
Confusing depreciation with devaluation.
The words sound alike.
Fix: Depreciation is a market-driven fall under a floating rate. Devaluation is a deliberate official cut under a fixed or pegged rate.
Getting the direction wrong when the rate is quoted as ₹ per $.
A higher number feels like a stronger currency.
Fix: If ₹ per $ rises, you need more rupees per dollar, so the rupee has weakened.
Drawing the J-curve with the dip after the improvement, or explaining it with the wrong cause.
Students memorise the shape but not the reason.
Fix: The dip comes first because short-run demand is inelastic and import costs rise at once. Volumes adjust later.
Ignoring inflation and growth effects.
The topic is treated as only a trade question.
Fix: Add a line on imported inflation and on the AD effect of higher net exports.

Worked examples

Example 1

The price elasticity of demand for a country's exports is 0.8 and for its imports is 0.5 (absolute values). The currency depreciates. Starting from a balanced trade position, explain the likely effect on the trade balance.

Show the solution

Sum the elasticities: 0.8 + 0.5 = 1.3.
Compare with 1: 1.3 > 1, so the Marshall-Lerner condition holds.
Volume responses are strong enough to outweigh the higher price of each unit of imports and the lower foreign-currency price of exports.
Add timing: in the short run the J-curve may cause a temporary worsening because elasticities are lower.

Answer: The trade balance improves in the long run because the elasticity sum of 1.3 exceeds 1. It may worsen briefly first (J-curve).

Example 2

An economy depreciates its currency. Explain two effects on inflation and one effect on growth.

Show the solution

Inflation effect 1: imported goods and raw materials cost more in domestic currency, so consumer prices and firms' costs rise (cost-push inflation).
Inflation effect 2: if export demand rises and the economy is near full capacity, higher aggregate demand adds demand-pull pressure.
Growth effect: cheaper exports and dearer imports raise net exports (X − M), which increases aggregate demand and output, provided the Marshall-Lerner condition holds and there is spare capacity.
Note a limit: if the economy relies on imported inputs, higher costs can reduce output and offset the gain.

Answer: Depreciation raises inflation through dearer imports and possibly stronger demand. It can raise growth through higher net exports, but the gain depends on elasticities, spare capacity and import dependence.

Exam tips

Write the Marshall-Lerner condition in full: the sum of the price elasticities of demand for exports and imports exceeds 1.
In MCQs, watch for the words 'short run' and 'immediately'. They usually point to the J-curve.
In written answers, give both sides and end with a judgement based on elasticities, time and spare capacity.
Sketch the J-curve with labelled axes: time on the horizontal axis, trade balance on the vertical axis, and the dip marked.
Link the exchange rate to AD = C + I + G + (X − M) to show the growth channel clearly.

Practice questions from Balance of payments and exchange rates

Exchange Rates and the Macroeconomy: frequently asked questions

What is the Marshall-Lerner condition in simple terms?

It says depreciation improves the trade balance only if the sum of the price elasticities of demand for exports and imports is greater than 1. It checks whether volume changes are large enough to outweigh price changes.

Why does the J-curve happen?

In the short run, contracts are fixed and buyers cannot switch quickly, so volumes barely change while import prices rise. The balance worsens first. As volumes adjust over time, the balance improves.

How does depreciation affect inflation?

It raises the domestic price of imports and imported inputs, which pushes up costs and consumer prices. Stronger export demand can add further pressure if the economy is near capacity.

Does a weaker currency always help growth?

No. It helps if export demand responds well and there is spare capacity. It can hurt if firms depend on imported inputs or hold foreign-currency debt.