The Marshall–Lerner condition is a key concept in international economics and trade that every forex trader should understand. This condition examines the relationship between a country’s exports, imports, and exchange rates to determine if currency devaluation can improve a nation’s balance of trade.

In this comprehensive guide, we will delve into the intricacies of the Marshall–Lerner condition, its implications for currency markets, and how traders can apply this model to their forex strategies.

What is the Marshall–Lerner Condition?

The Marshall–Lerner condition states that for a currency devaluation to cause an improvement in a country’s balance of trade, the sum of demand elasticities for exports and imports must exceed one. This means that a percentage change in a country’s currency value must lead to a larger percentage change in the demand for that country’s exports and imports.

In mathematical terms, the Marshall–Lerner condition is:

Exports Demand Elasticity + Imports Demand Elasticity > 1

If this inequality holds true, then currency depreciation will improve the trade balance by increasing exports and decreasing imports. This is known as meeting the Marshall–Lerner condition.

The condition is named after British economists Alfred Marshall and Abba Lerner, who analyzed the relationship between exchange rates and trade balances in the early 20th century.

The Intuition Behind Marshall–Lerner

The intuition behind the Marshall–Lerner condition is straightforward – currency devaluation will only aid the trade balance if price elasticities of exports and imports are sufficiently high.

Price elasticity measures the sensitivity of demand or supply to changes in price. For exports, it shows the percentage change in foreign demand when export prices change by 1%. For imports, it reflects the percentage change in domestic demand when import prices change by 1%.

  • Inelastic demand means changes in price have a smaller effect on quantity demanded.
  • Elastic demand means changes in price have a larger effect on quantity demanded.

For currency devaluation to improve trade balances:

  • Export demand must be elastic – lower export prices should substantially increase foreign demand.
  • Import demand must be elastic – higher import prices should substantially decrease domestic demand.

If these elasticities are low (inelastic demand), trade volumes will not change much despite the currency devaluation. So the Marshall–Lerner condition requires export/import demand to be sufficiently elastic.

Why Does the Marshall–Lerner Condition Matter?

The Marshall–Lerner condition has crucial implications for forex trading and international economics. Here are some key reasons why it matters:

Evaluating Currency Devaluations

The condition provides a test for whether a country’s devaluation of its currency will achieve the desired effect of improving exports and reducing imports. Traders can assess whether the Marshall–Lerner condition holds to gauge the potential effectiveness of a currency devaluation.

Understanding Trade Impacts

It demonstrates the importance of trade elasticities in determining a currency’s impact on trade flows. Traders must analyze export/import demand elasticities to understand how exchange rate swings affect cross-border trade.

Forecasting Price Changes

The condition shows that currency depreciation may not necessarily lead to lower export prices and higher import prices, due to inelasticities. Traders can factor elasticities into pricing forecasts.

Modeling Currency Fair Value

Since trade flows influence currency supply and demand, the Marshall–Lerner condition can improve models for determining a currency’s fair value. Factoring elasticities can produce more accurate valuations.

Sizing Currency Misalignments

Elasticity estimates help traders size currency misalignments. Currencies may be overvalued or undervalued based on the trade effects predicted by the Marshall–Lerner condition.

Informing Monetary Policy

Central banks consider trade competitiveness when setting monetary policy. The condition guides policymakers on whether devaluation may improve trade balances and boost the economy.

Analyzing Competitiveness

Export competitiveness depends on price elasticity of foreign demand. The Marshall–Lerner condition quantifies competitiveness impacts based on trade elasticities.

As shown above, the Marshall–Lerner condition has far-reaching analytical applications for traders and economists. Next, we will explore the condition in more depth.

Key Components of the Marshall–Lerner Condition

To fully grasp the Marshall–Lerner condition, traders must understand these key concepts and components:

Price Elasticity of Demand

As discussed earlier, price elasticity of demand (PED) measures the sensitivity of quantity demanded to changes in price. It is calculated as:

PED = % Change in Quantity Demanded / % Change in Price

For example, if a 10% drop in the price of UK textile exports leads to a 20% increase in foreign demand, the PED for UK textile exports is 20%/10% = 2.

The higher the PED, the more elastic the demand. If PED is above 1, demand is elastic. If it is below 1, demand is inelastic.

Currency Devaluation

This refers to a deliberate downward adjustment in a currency’s exchange rate value by the central bank via market interventions. For example, the Bank of Japan weakening the yen from 115 to 125 per US dollar.

Currency devaluations aim to stimulate exports and discourage imports to correct trade deficits. But the Marshall–Lerner condition must be met for these outcomes.

J-Curve Effect

This refers to the short-term trend of a country’s trade balance worsening initially after currency devaluation before improving, creating a J-shaped curve.

In the near-term, the volume impact of currency devaluation is small due to low elasticities. With time, trade volumes adjust more meaningfully per the Marshall–Lerner condition.

Partial vs Total Elasticity

Partial elasticity considers demand changes due to price changes of one product only, holding other factors equal. Total elasticity incorporates demand shifts across all export/import products.

Since many products are traded, the Marshall–Lerner condition is generally applied using total elasticities of a country’s overall export/import demand.

Time Horizon

The Marshall–Lerner condition may not hold in the short run due to rigidities but plausibly holds in the long run as trade volumes become more price flexible. The time horizon affects whether devaluation improves trade balances.

How to Calculate the Marshall–Lerner Condition

Traders can follow these steps to calculate and analyze the Marshall–Lerner condition for a currency:

Step 1: Estimate Export/Import Demand Elasticities

Use historical trade data to estimate export and import demand elasticities. Analyze volume changes against currency price changes. Individual product data can assess partial elasticities.

Step 2: Sum the Elasticities

Add the total export demand and total import demand elasticities. This will give the combined trade elasticity.

Step 3: Evaluate the Condition

If the combined elasticity exceeds 1, the Marshall–Lerner condition holds and devaluation should improve trade balance. If it is below 1, the condition does not hold.

Step 4: Assess the Time Frame

Determine if the short or long run. The condition may not hold in the short run due to rigidities.

Step 5: Account for Other Factors

Consider other macroeconomic factors that could influence trade flows like trade policies and growth. Isolate the currency impact through regression analysis.

Step 6: Forecast Trade Impacts

Use the elasticities to forecast expected changes in exports and imports from a currency devaluation. This helps traders position for anticipated price movements.

By following these steps, traders can judiciously apply the Marshall–Lerner condition in their currency analysis.

Limitations of the Marshall–Lerner Condition

While the Marshall–Lerner condition is a useful framework, traders should be aware of these limitations:

  • Assumes other factors like tariffs and GDP are fixed – does not account for shifting macro conditions.
  • Focuses only on quantity changes, although currency swings also affect profit margins.
  • Uses overall trade elasticities, although elasticities differ across industries and product categories.
  • Estimating elasticities with precision is challenging.
  • Does not specify the size of currency change needed to influence trade flows.
  • Difficult to analyze hyperinflationary economies.
  • Cannot predict exchange rate movements, only the resulting trade impacts.

Despite these constraints, the condition remains a valuable tool for traders in assessing currency trends. Traders can compensate for limitations by using elasticity ranges in analysis and combining the condition with other forex trading models.

Real World Examples of the Marshall–Lerner Condition

The Marshall–Lerner condition has played out in various instances of currency devaluations worldwide. Here are some key examples:

Japan – Early 2010s

Facing trade deficits, Japan deliberately weakened the yen from 80 to over 120 against the USD. Export volumes surged given highly elastic foreign demand, meeting the Marshall–Lerner condition.

UK – 2008 to 2009

The pound’s sharp decline versus the euro failed to improve the UK’s trade balance, as eurozone demand was inelastic. This violated the Marshall–Lerner condition.

China – 2015 to 2016

China guided the yuan lower against the USD, hoping to boost exports. But with inelastic foreign demand, the move worsened China’s trade surplus contrary to the condition.

Singapore – Mid 1980s

Singapore gradually depreciated against its trade partners. Strong elasticities allowed this to reduce deficits as the Marshall–Lerner condition held.

Mexico – Late 1990s

A sharp peso devaluation led to higher export volumes to the U.S. This validated Mexico meeting the Marshall–Lerner condition, despite short-term trade deterioration.

These examples demonstrate the relevance of the Marshall–Lerner condition in assessing real-world currency devaluations across various countries.

Applying the Marshall–Lerner Condition in Forex Trading

For forex traders, properly applying the Marshall-Lerner condition requires following these best practices:

  • Use the condition to evaluate the potential effectiveness of a trade-related currency intervention. If the condition does not hold, devaluation may not have the desired impacts.
  • Carefully estimate export and import demand elasticities for major traded goods and trading partners. The more accurate the elasticity inputs, the better the analysis.
  • Assess elasticities over both short and long-term horizons. The effectiveness of devaluation policies often changes over time.
  • Account for other macroeconomic factors influencing trade beyond just the exchange rate in isolation. Use a holistic assessment of trade trends.
  • Combine the condition with other currency valuation models like purchasing power parity (PPP) and interest rate parity. Use it as one input in a multifaceted analysis.
  • Avoid over-reliance on the condition. While useful, it cannot predict currency movements and has limitations like any model.

Using the Marshall–Lerner condition judiciously allows forex traders to make more informed bets on the complex interplay between exchange rates and international trade flows.


The Marshall–Lerner condition illuminates the significant role of trade elasticities in linking a currency’s value to trade balances. When combined with sound judgment, this condition gives traders a leg up in analyzing the forex impacts of trade flows and exchange rates.

By fully grasping the intuition, calculations, real-world examples, and applications of the Marshall–Lerner condition, forex traders position themselves for success. Just remember – no economic model offers a silver bullet. Use the Marshall–Lerner condition as one input among many when developing your unique trading strategies.