Monetary Approach to Exchange Rates: Understanding Long-term Trends

Exchange rates are one of the most important prices in any open economy, influencing everything from inflation to trade balances. While many factors drive currency values in the short run, the monetary approach to exchange rate determination offers a powerful framework for understanding long-term currency trends. This approach connects exchange rates directly to monetary fundamentals like money supply and demand, providing insights into why currencies eventually move toward their fundamental values.

What is the monetary approach to exchange rates? 🔗

The monetary approach views exchange rates primarily as the relative price of two national monies. Rather than focusing on trade flows or short-term capital movements, this theory argues that currency values are fundamentally determined by the supply and demand for money in each economy. When monetary conditions change in one country relative to another, exchange rates adjust to restore equilibrium.

This approach is considered “monetary” because it places money markets at the center of exchange rate determination. It emerged in the 1970s following the collapse of the Bretton Woods fixed exchange rate system, when economists needed new frameworks to understand floating exchange rates.

Core assumptions of the monetary approach 🔗

• Perfect capital mobility: Financial assets can move freely between countries, allowing interest rate parity to hold.
• Purchasing power parity (PPP): Over the long run, exchange rates adjust to equalize the purchasing power of different currencies.
• Stable money demand functions: The relationship between money demand, income, prices, and interest rates remains relatively predictable.
• Flexible prices: Prices can adjust to clear markets, especially in the long run.

The fundamental equation of the monetary approach 🔗

The monetary approach can be expressed through a relatively straightforward equation that connects exchange rates to money supply and demand in two countries. If we take the exchange rate between the domestic currency and a foreign currency (e.g., rupees per dollar), the basic relationship is:

Exchange Rate = (Domestic Money Supply / Foreign Money Supply) × (Foreign Money Demand / Domestic Money Demand)

This formula shows that when the domestic money supply increases relative to foreign money supply, the domestic currency tends to depreciate. Conversely, when domestic money demand increases relative to foreign money demand, the domestic currency tends to appreciate.

Money demand and its determinants 🔗

To understand this approach fully, we need to recognize what drives money demand. In most monetary models, money demand depends on:

• Price level: Higher prices mean people need more money for transactions.
• Real income/output: As economic activity increases, the demand for money for transactions rises.
• Interest rates: Higher interest rates reduce money demand as people shift to interest-bearing assets.

When we incorporate these factors into our exchange rate model, we can see how changes in output, prices, and interest rates affect currency values through their impact on money demand.

How monetary factors influence exchange rates 🔗

Effects of changes in money supply 🔗

One of the most direct implications of the monetary approach is that increases in a country’s money supply, other things being equal, lead to proportional depreciation of its currency. For example, if India’s money supply grows 10% faster than the US money supply, the rupee would be expected to depreciate by approximately 10% against the dollar in the long run.

This occurs through a process often called “monetary neutrality.” When a central bank increases the money supply:

1. Initially, there’s excess money in the economy
2. People spend this excess money, pushing up prices
3. As domestic prices rise, domestic goods become less competitive
4. The currency depreciates to restore equilibrium

We’ve seen this relationship play out historically in countries experiencing high inflation. For instance, countries like Zimbabwe or Venezuela that dramatically expanded their money supplies saw rapid currency depreciation as a result.

Effects of changes in output/income 🔗

Economic growth also impacts exchange rates through the monetary channel. When a country’s real output increases:

• Money demand rises as people need more currency for increased transactions
• With a fixed money supply, this increased demand tends to strengthen the currency

For example, if India experiences stronger productivity growth than the United States, the increased demand for rupees (to facilitate the higher level of economic transactions) would put upward pressure on the rupee relative to the dollar, assuming money supplies grow at similar rates.

Effects of interest rate changes 🔗

In the monetary approach, interest rates affect exchange rates differently than in some other models. While higher interest rates often attract capital flows that strengthen a currency in the short run, the monetary approach focuses on how interest rates affect money demand:

• Higher interest rates reduce the demand for money (people prefer interest-bearing assets)
• Lower money demand, with constant money supply, can lead to currency depreciation

This counterintuitive result highlights the difference between short-term and long-term effects. In the short run, higher interest rates may strengthen a currency through capital inflows, but in the long run, if they’re caused by higher inflation expectations, they may signal future currency weakness.

Purchasing power parity and the monetary approach 🔗

Purchasing power parity (PPP) is a critical component of the monetary approach. It suggests that in the long run, exchange rates adjust to equalize the price of goods across countries. The two versions of PPP are:

Absolute PPP 🔗

Absolute PPP states that the exchange rate between currencies should equal the ratio of price levels in the two countries. For example, if a basket of goods costs 8,000 rupees in India and $100 in the US, the PPP exchange rate would be 80 rupees per dollar.

While absolute PPP rarely holds perfectly due to transportation costs, trade barriers, and non-tradable goods, it provides a theoretical anchor for long-run exchange rates.

Relative PPP 🔗

Relative PPP focuses on changes rather than levels. It suggests that the percentage change in the exchange rate should equal the difference in inflation rates between countries. For example, if India has 6% inflation while the US has 2%, relative PPP predicts the rupee should depreciate by approximately 4% against the dollar.

Relative PPP tends to hold better over longer timeframes, making it particularly relevant to the monetary approach’s long-run focus.

Mathematical representation of the monetary approach 🔗

For those interested in the formal representation, the monetary approach can be expressed using the following equations:

First, we have the domestic money market equilibrium:

M^d = M^s

M^d = P × L(Y, i)

Where:

• M^d is money demand
• M^s is money supply
• P is the price level
• L(Y, i) represents the demand for real money balances as a function of real income (Y) and interest rate (i)

The same relationship applies in the foreign country. Combining these with the PPP condition (E = P/P*, where E is the exchange rate and P* is the foreign price level), we get:

E = (M/M*) × [L*(Y*, i*)/L(Y, i)]

This equation shows that the exchange rate depends on relative money supplies and relative money demands between the two countries.

Empirical evidence and limitations 🔗

Support for the monetary approach 🔗

Evidence for the monetary approach is strongest when examining:

• High inflation episodes: Currency values in hyperinflationary economies clearly reflect monetary conditions.
• Very long time periods: Over decades, exchange rates tend to follow the patterns predicted by monetary fundamentals.
• Cross-country comparisons: Countries with consistently higher money growth typically experience currency depreciation.

For example, studies have shown that over periods of 5+ years, changes in relative money supplies explain a significant portion of exchange rate movements between major currencies.

Challenges to the monetary approach 🔗

Despite its theoretical elegance, the monetary approach faces several challenges:

• Short-run volatility: Exchange rates fluctuate much more than monetary fundamentals in the short run.
• The disconnect puzzle: Researchers have found a weak contemporaneous relationship between exchange rates and macroeconomic fundamentals.
• Identification of money demand: It’s challenging to precisely measure and model money demand, especially as financial innovations change how people use money.
• PPP deviations: Purchasing power parity often fails to hold in the short and medium term.

These limitations have led economists to view the monetary approach as more useful for understanding long-run trends than short-term fluctuations.

Policy implications of the monetary approach 🔗

The monetary approach offers several important insights for policymakers:

Monetary policy autonomy 🔗

Under floating exchange rates, countries retain monetary policy independence, but at the cost of exchange rate fluctuations. The monetary approach explains why attempts to simultaneously control both money supply and exchange rates are generally unsuccessful in the long run.

Inflation targeting and exchange rates 🔗

Countries that maintain lower inflation than their trading partners can expect long-term currency appreciation, according to the monetary approach. This helps explain why currencies of countries with credible inflation-targeting regimes often strengthen over time.

Foreign exchange interventions 🔗

The monetary approach suggests that sterilized foreign exchange interventions (where central banks buy or sell foreign currency without changing the domestic money supply) may have limited long-term effects on exchange rates. Only interventions that affect relative money supplies would have lasting impacts.

Real-world application: Case study of inflation and exchange rates 🔗

Consider the case of Turkey in recent years. Between 2018 and 2023, Turkey experienced significantly higher inflation than the United States and other major economies. This inflation coincided with rapid expansion of Turkey’s money supply.

As the monetary approach would predict, the Turkish lira depreciated substantially against the dollar during this period. While many factors influenced this depreciation, the divergence in monetary conditions between Turkey and the US was a fundamental driver of the long-term trend.

This example illustrates how the monetary approach can help us understand major currency trends, even if it doesn’t explain all the short-term fluctuations.

Conclusion: The enduring relevance of the monetary approach 🔗

Despite its limitations, the monetary approach to exchange rate determination provides an invaluable framework for understanding long-term currency movements. By focusing on monetary fundamentals, it helps explain why currencies of countries with high money growth and inflation tend to depreciate over time.

While other factors like productivity differentials, risk premiums, and market sentiment drive exchange rates in the short run, the monetary approach reminds us that currencies cannot permanently deviate from their fundamental values determined by monetary conditions.

For students of macroeconomics, policymakers, and investors alike, the monetary approach offers essential insights into one of the most important prices in any open economy-the exchange rate.

What do you think? How might central bank digital currencies change the relationship between money supply and exchange rates in the future? Can you think of countries where the monetary approach seems to explain exchange rate movements particularly well?