Thirlwall’s Law (Currency Trading)

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Written By
Dan Buckley
Dan Buckley is an US-based trader, consultant, and part-time writer with a background in macroeconomics and mathematical finance. He trades and writes about a variety of asset classes, including equities, fixed income, commodities, currencies, and interest rates. As a writer, his goal is to explain trading and finance concepts in levels of detail that could appeal to a range of audiences, from novice traders to those with more experienced backgrounds.

Thirlwall’s Law, named after the British economist Anthony Thirlwall, is a principle in macroeconomics that explores the relationship between economic growth and the balance of payments in an economy.

It posits that the long-term growth rate of an economy is directly related to the growth rate of exports divided by the income elasticity of demand for imports.

In simple terms, if a country’s exports grow and the demand for its imports doesn’t grow too fast, the country can have stable economic growth.

The law helps to understand how much a country can grow without facing issues in its balance of payments (the record of all economic transactions between the residents of the country and the world).

We’ll explain the implications for currency trading.


Key Takeaways – Thirlwall’s Law

  • Thirlwall’s Law suggests countries might devalue their currency to boost exports, leading to higher economic growth.
  • A change in exchange rates can influence the demand for imports. A depreciation in domestic currency can make imports pricier, potentially reducing import demand and improving the trade balance, offering trading opportunities.
  • Consistent economic growth, as indicated by Thirlwall’s Law, might attract more foreign investment, leading to currency appreciation.

Mathematical Representation of Thirlwall’s Law

The law can be mathematically represented as:


G = (X/M) * (PM / PX)



  • G is the sustainable growth rate of the economy
  • X is the growth rate of exports
  • M is the income elasticity of demand for imports
  • PM  is the price of imports
  • PX is the price of exports

Conceptual Explanation of Thirlwall’s Law

Balance of Payments Constraint

Thirlwall’s Law is grounded in the idea that an economy’s growth is constrained by its balance of payments.

A country cannot sustain a growth rate that consistently leads to a trade deficit, as it would eventually face issues with debt and foreign exchange reserves.

Income Elasticity of Demand for Imports

This refers to the responsiveness of the demand for imports to a change in national income.

If the income elasticity of demand for imports is high, it means that as the economy grows, it will import a lot, potentially leading to a trade deficit.

Growth Rate of Exports

The growth rate of exports is an important factor determining the sustainable growth rate of an economy.

A higher growth rate of exports allows for a higher sustainable growth rate, as it brings in foreign exchange which can be used to finance imports.


Implications and Criticisms of Thirlwall’s Law

Policy Implications

Thirlwall’s Law suggests that if a country wants to grow faster without facing a balance of payments crisis, it needs to either:

  • increase the growth rate of exports, or
  • reduce the income elasticity of demand for imports

Doing the latter could possibly be done through industrial policies that promote domestic production.


Critics argue that the law is too simplistic and does not consider other factors that can influence the balance of payments and economic growth, such as capital flows, exchange rate policies, and technological advancements.


Applications of Thirlwall’s Law

Development Economics

Thirlwall’s Law is often used in development economics to explain the growth trajectories of different countries, especially those with developing economies.

Trade Policy

The law can influence trade policies, encouraging countries to focus on boosting exports and substituting imports with domestic production to sustain higher growth rates.


Thirlwall’s Law and Currency Trading

Let’s look into how this law interacts with exchange rate dynamics.

As noted, Thirlwall’s Law posits that a country’s sustainable economic growth rate is closely tied to the rate of growth of its exports, moderated by the income elasticity of demand for its imports.

In essence, it’s a theory that links economic growth with trade dynamics.

Now, how does this tie into exchange rates?


Exchange Rate Dynamics: The Connection with Thirlwall’s Law

Here’s the breakdown:

Competitive Devaluation

A country might engage in competitive devaluation to boost its export growth rate.

According to Thirlwall’s Law, a higher export growth rate can lead to a higher sustainable growth rate for the economy.

As a currency trader, spotting the signs of a potential devaluation can be a golden opportunity to make profitable trades.

Import Demand Sensitivity

Thirlwall’s Law highlights the role of the income elasticity of demand for imports.

A change in exchange rates can influence this elasticity, thereby affecting the trade balance.

For instance, a depreciation in the domestic currency can make imports more expensive, potentially reducing the demand for imports and improving the trade balance, at least in the short term.

Capital Flows and Investment

Changes in exchange rates can influence capital flows and foreign investment.

A country experiencing steady economic growth (as predicted by Thirlwall’s Law) might attract more foreign investment, leading to an appreciation of its currency.

As a trader, keeping an eye on economic growth trends can help you anticipate potential movements in exchange rates.

Trading Strategy Consideration from Thirlwall’s Law

Given the insights from Thirlwall’s Law, here are some strategies you might consider:

Long-Term Positioning

Identify currencies of countries with strong export growth and favorable trade balances for long-term positions.

Hedging Against Volatility

Understanding the implications of Thirlwall’s Law can help you hedge your portfolio against potential volatility arising from shifts in trade dynamics and exchange rate policies.

Many pay attention to the nominal value of their portfolio. They pay much less attention to their currency risks.

Correlation Analysis

Conduct a correlation analysis between economic growth rates, trade balances, and currency values to better understand identify potential trading opportunities.



Thirlwall’s Law offers a unique perspective on the relationship between economic growth and the balance of payments, emphasizing the role of trade dynamics in determining sustainable growth rates.

While it might not be a mainstream concept, it provides insights, especially in the context of developing economies and their growth strategies.