Exchange rates

Intuition [Beginner]

An exchange rate is the price of one country's currency in terms of another's. If the exchange rate between the US dollar and the Japanese yen is 150, it means one dollar buys 150 yen (or equivalently, one yen costs about $0.0067).

Exchange rates matter because they determine how much foreign goods cost and how much domestic goods cost for foreigners. If the dollar strengthens against the yen (the rate goes from 150 to 170), American tourists find Japan cheaper, Japanese tourists find America more expensive, US exporters find it harder to sell to Japan, and Japanese exporters find it easier to sell to the US.

There are three main exchange rate systems:

1. Floating: The exchange rate is determined by supply and demand in the foreign exchange market. The central bank does not intervene (or rarely does). Most major currencies (dollar, euro, yen, pound) float against each other.
2. Fixed (pegged): The government or central bank sets a specific exchange rate and defends it by buying and selling currency. China historically pegged the yuan to the dollar; some countries peg to the euro.
3. Managed float: The exchange rate mostly floats, but the central bank intervenes occasionally to smooth out volatility or prevent extreme movements. Many developing countries use this system.

Exchange rates change for many reasons: differences in interest rates between countries, differences in inflation rates, trade flows, investment flows, speculation, and central bank intervention. Like any price, the exchange rate is determined by supply and demand -- but the foreign exchange market is the largest and most liquid market in the world, with over $7 trillion traded daily.

Visual [Beginner]

Exchange Rate Systems

  FLOATING                   FIXED                      MANAGED FLOAT
  +------------------+       +------------------+       +------------------+
  | Market decides   |       | Central bank     |       | Market mostly    |
  | the rate         |       | sets the rate    |       | decides, central |
  |                  |       | and defends it   |       | bank intervenes  |
  | Rate moves       |       |                  |       | occasionally     |
  | continuously     |       | Rate stays at    |       |                  |
  |                  |       | target unless    |       | Smooths extreme  |
  | Examples: USD,   |       | defense fails    |       | moves            |
  | EUR, JPY, GBP    |       |                  |       |                  |
  +------------------+       | Examples: Saudi  |       | Examples: Many   |
                             | riyal, Danish    |       | emerging market  |
                             | krone            |       | currencies       |
                             +------------------+       +------------------+


  What happens when a currency APPRECIATES (gets stronger)?

  Imports become cheaper      Exports become more expensive
  Consumers benefit           Domestic producers suffer
  Inflation tends to fall     Trade deficit may widen
  Foreign travel cheaper      Tourism from abroad falls

  What happens when a currency DEPRECIATES (gets weaker)?

  Imports become more expensive    Exports become cheaper
  Consumers face higher prices     Domestic producers benefit
  Inflation tends to rise          Trade deficit may narrow
  Foreign travel more expensive    Tourism from abroad rises

Worked Example [Beginner]

A US company wants to buy machinery from Germany that costs 100,000 euros.

Scenario 1: Exchange rate is $1.05 per euro. Cost in dollars = $100,000\times 1.05=\$105,000$

Scenario 2: The dollar depreciates. Exchange rate moves to $1.20 per euro. Cost in dollars = $100,000\times 1.20=\$120,000$

The same machinery now costs $15,000 more. The US buyer has three options: absorb the cost (reducing profit), pass it to customers (raising prices), or find a domestic supplier.

Now consider the German exporter. In Scenario 1, they receive 100,000 euros. In Scenario 2, they still receive 100,000 euros. But US demand for their machinery may fall because it is now more expensive for American buyers.

Scenario 3: The dollar appreciates. Exchange rate moves to $0.90 per euro. Cost in dollars = $100,000\times 0.90=\$90,000$

Now German machinery is cheaper for Americans. US demand rises. But the German exporter still receives 100,000 euros; they do not directly benefit from the exchange rate change. The mechanism works through quantity demanded, not price received.

Check your understanding [Beginner]

Formal Definition [Intermediate+]

Exchange rate notation

The nominal exchange rate $e$ is the domestic-currency price of foreign currency. An increase in $e$ is a depreciation of the domestic currency; a decrease is an appreciation.

The real exchange rate adjusts for price level differences:

$$ϵ=\frac{e\times P^{\ast }}{P}$$

where $P$ is the domestic price level and $P^{\ast }$ is the foreign price level. The real exchange rate measures the relative price of foreign goods in terms of domestic goods. If $ϵ$ rises, foreign goods are relatively more expensive and the domestic economy is more competitive.

Purchasing power parity (PPP)

Absolute PPP states that the exchange rate should equalize the price of identical goods across countries:

$$e=\frac{P}{P^{\ast }}$$

If a basket of goods costs $100 in the US and 10,000 yen in Japan, then $e=100/10,000=0.01$ dollars per yen (or 100 yen per dollar).

Relative PPP states that exchange rate changes reflect inflation differentials:

$$\frac{\Delta e}{e}=\pi -{\pi }^{\ast }$$

where $\pi$ is domestic inflation and ${\pi }^{\ast }$ is foreign inflation. If US inflation is 5% and Japanese inflation is 1%, the dollar should depreciate by approximately 4% against the yen.

PPP holds well in the long run (decades) but poorly in the short run. The most famous illustration is the Big Mac Index, published by The Economist, which compares the price of a Big Mac across countries to assess whether currencies are over- or undervalued relative to PPP.

Interest rate parity

Covered interest rate parity (CIP):

$$1+i=\frac{F}{S}(1+i^{\ast })$$

where $i$ is the domestic interest rate, $i^{\ast }$ is the foreign interest rate, $S$ is the spot exchange rate, and $F$ is the forward exchange rate. CIP is enforced by arbitrage and holds closely in practice.

Uncovered interest rate parity (UIP):

$$1+i=\frac{E[S_{t+1}]}{S_t}(1+i^{\ast })$$

UIP says that the expected return from investing domestically should equal the expected return from converting to foreign currency, investing abroad, and converting back at the expected future rate. UIP does not hold well empirically -- high-interest-rate currencies tend to appreciate, not depreciate as UIP predicts (the "forward premium puzzle").

The Mundell-Fleming model

An extension of IS-LM to an open economy. Key results:

• Floating exchange rate: Monetary policy is effective (expansion shifts LM right, depreciating the currency and boosting net exports). Fiscal policy is less effective (expansion shifts IS right, appreciating the currency and crowding out net exports).
• Fixed exchange rate: Monetary policy is ineffective (the central bank must defend the peg, neutralizing monetary changes). Fiscal policy is effective (expansion shifts IS right, and the central bank accommodates by expanding the money supply to maintain the peg).

The impossible trinity (trilemma)

A country cannot simultaneously have all three of:

1. A fixed exchange rate
2. Free capital mobility
3. Independent monetary policy

It can choose any two. This constraint shapes the choice of exchange rate regime.

Key Concepts [Intermediate+]

• Nominal exchange rate: The price of one currency in terms of another.
• Real exchange rate: The nominal rate adjusted for price level differences between countries. Measures competitiveness.
• Appreciation: A currency becomes more valuable (buys more foreign currency). Makes imports cheaper and exports more expensive.
• Depreciation: A currency becomes less valuable (buys less foreign currency). Makes imports more expensive and exports cheaper.
• Floating exchange rate: Determined by market forces without central bank intervention.
• Fixed exchange rate: Set by the central bank and maintained through intervention.
• Purchasing power parity (PPP): The theory that exchange rates adjust to equalize the purchasing power of currencies across countries.
• Interest rate parity: The relationship between interest rate differentials and forward exchange rates.
• Impossible trinity: A country cannot have a fixed exchange rate, free capital flows, and independent monetary policy simultaneously.
• Currency crisis: A sharp, sudden depreciation or devaluation, often caused by a speculative attack when markets doubt the central bank's ability or commitment to defend a fixed rate.

Academic Perspectives [Master]

Neoclassical / mainstream view

Mainstream international economics views exchange rates as prices determined by supply and demand in the foreign exchange market. Under flexible exchange rates, the market clears without central bank intervention. The equilibrium rate reflects fundamentals: relative price levels (PPP), relative interest rates (interest rate parity), relative productivity growth, trade balances, and capital flows.

The mainstream view generally favors floating exchange rates for large economies, because they allow independent monetary policy and automatic adjustment to shocks. Fixed rates are seen as appropriate for small open economies, countries with weak monetary institutions (importing credibility by pegging to a strong currency), or regions with deep economic integration (the eurozone).

Keynesian view

Keynesians emphasize that exchange rates can deviate from fundamentals for extended periods due to speculation, herd behavior, and self-fulfilling expectations. These misalignments can cause real economic damage: an overvalued currency hurts exporters and destroys manufacturing capacity; an undervalued currency fuels inflation and asset bubbles.

Keynesians are more sympathetic to managed exchange rates and capital controls than the mainstream. If floating rates produce excessive volatility or persistent misalignment, policy intervention may be warranted. John Maynard Keynes was an advocate of the Bretton Woods system of fixed but adjustable exchange rates, which he helped design.

Austrian view

Austrian economists are generally skeptical of government manipulation of exchange rates. Under a gold standard or commodity money system, exchange rates would be largely determined by the relative gold content of currencies, providing stability without central bank intervention. The current system of floating fiat currencies, in the Austrian view, allows governments to inflate their money supply and depreciate their currency to reduce the real burden of debt -- a hidden tax on savers and creditors.

Austrians view currency crises as the inevitable result of unsustainable monetary expansion under fixed exchange rate regimes. The crisis is not the problem; it is the market correcting the previous distortion.

Marxian perspective

Marxian economists analyze exchange rates in terms of power relations between core and periphery countries. The dominance of the US dollar as the world's reserve currency gives the United States an "exorbitant privilege" (a term coined by French finance minister Valery Giscard d'Estaing): it can borrow in its own currency and run persistent trade deficits, while developing countries must borrow in dollars and face currency crises when their currencies depreciate against the dollar.

Currency crises in developing countries (Mexico 1994, East Asia 1997, Argentina 2001) are analyzed as episodes where speculative capital flows, denominated in foreign currency, overwhelm weak domestic financial systems. The resulting depreciations increase the real burden of foreign-denominated debt, deepening the crisis. The structure of the international monetary system systematically disadvantages countries at the periphery.

Institutional perspective

Institutional economists study the governance of the international monetary system. The IMF's role in managing exchange rate crises, the conditions attached to its loans (structural adjustment programs), and the distribution of voting power in international financial institutions all reflect institutional power dynamics.

The choice of exchange rate regime is not purely a technical decision. It reflects domestic political coalitions: exporters prefer a weaker currency, importers and consumers prefer a stronger one, and the financial sector prefers stability and predictability. The exchange rate regime that emerges reflects which coalition has more political influence.

Behavioral perspectives

Behavioral finance has documented that exchange rate markets exhibit patterns inconsistent with rational expectations: momentum (currencies that have appreciated tend to continue appreciating), overreaction to news, and herding behavior among traders. These findings challenge the efficient market hypothesis as applied to foreign exchange.

Survey data on exchange rate expectations show that professional forecasters are poor at predicting exchange rate movements. Most models (including PPP and interest rate parity) outperform random walk predictions only at long horizons (3-5 years or more). In the short run, exchange rates are difficult to distinguish from a random walk.

Historical Context [Master]

• Gold standard (1870s-1914): Exchange rates were fixed within narrow bands determined by the gold content of each currency. The system provided remarkable stability but required countries to subordinate domestic policy to the gold constraint. It collapsed with World War I.
• Interwar period (1918-1939): Attempts to restore the gold standard failed. Competitive devaluations and protectionism contributed to the Great Depression. The experience discredited fixed rates for a generation.
• Bretton Woods (1944-1971): A system of fixed exchange rates pegged to the US dollar, which was convertible to gold at $35/oz. Countries could adjust their pegs in cases of "fundamental disequilibrium." The system provided stability during postwar reconstruction but collapsed when Nixon suspended gold convertibility in 1971.
• Floating era (1973-present): Major currencies have floated since the collapse of Bretton Woods. The period has seen large swings in exchange rates, including the Plaza Accord (1985, coordinated depreciation of the dollar) and the Louvre Accord (1987, attempt to stabilize rates).
• European Monetary Union (1999): Eleven European countries adopted the euro, irrevocably fixing their exchange rates. The euro eliminated intra-European exchange rate fluctuations but eliminated national monetary policy. The eurozone crisis (2010-2015) highlighted the costs of a one-size-fits-all monetary policy.
• Asian financial crisis (1997-1998): Speculative attacks forced Thailand, Indonesia, South Korea, and other countries to abandon their dollar pegs. Currencies lost 30-80% of their value. The crisis demonstrated the vulnerability of fixed exchange rates to capital flight in a world of mobile capital.
• Argentine crisis (2001-2002): Argentina's currency board (1 peso = 1 dollar) became unsustainable. The country defaulted on its debt and devalued the peso, which lost 75% of its value. A classic example of the impossible trinity.
• Swiss franc unpegging (2015): The Swiss National Bank unexpectedly abandoned its cap on the franc against the euro, causing the franc to appreciate 30% in minutes. The event illustrated the difficulty of maintaining fixed rates against market pressure.

Bibliography [Master]

• Dornbusch, R. (1976). Expectations and exchange rate dynamics. Journal of Political Economy, 84(6), 1161-1176.
• Eichengreen, B. (1996). Globalizing Capital: A History of the International Monetary System. Princeton University Press.
• Kenen, P. B. (1994). Exchange Rates and the Monetary System. Edward Elgar.
• Krugman, P. R. (1979). A model of balance-of-payments crises. Journal of Money, Credit and Banking, 11(3), 311-325.
• McKinnon, R. I. (1993). The rules of the game: International money in historical perspective. Journal of Economic Literature, 31(1), 1-44.
• Obstfeld, M., & Rogoff, K. (1996). Foundations of International Macroeconomics. MIT Press.
• Sarno, L., & Taylor, M. P. (2002). The Economics of Exchange Rates. Cambridge University Press.