Exchange Rates

The Foreign Exchange Market

On September 26, 2022, the British pound crashed to $1.035 against the U.S. dollar, its lowest level in recorded history. The catalyst was a "mini-budget" announced by Chancellor Kwasi Kwarteng two days earlier, a package of unfunded tax cuts totaling roughly 45 billion pounds that spooked currency traders and bond investors simultaneously. Within hours of the announcement, hedge funds and institutional investors dumped sterling in massive volumes. The Bank of England was forced into emergency gilt purchases to stabilize the bond market. Kwarteng was fired within weeks, and the entire episode demonstrated with brutal clarity how quickly the foreign exchange (forex) market can punish a policy misstep. Over $7.5 trillion changes hands daily on this market, dwarfing every stock exchange on the planet combined.

The exchange rate is simply a price: how much of one currency trades for another. Foreigners demand dollars when they want to purchase American goods, services, or financial assets. A BMW plant in Munich importing American-made microchips needs dollars to pay the supplier. A Japanese pension fund buying U.S. Treasury bonds needs dollars to settle the trade. Every foreign purchase of American exports or American assets creates demand for dollars in the forex market.

Americans supply dollars whenever they buy foreign goods, services, or assets. Purchasing a German car, Korean electronics, or booking a vacation in Mexico sends dollars into the forex market in exchange for euros, won, or pesos. Standard supply-and-demand logic applies. Equilibrium occurs where the quantity of dollars demanded equals the quantity supplied, and that intersection determines the exchange rate. On the graph, the vertical axis shows the dollar's price in foreign currency (euros per dollar) while the horizontal axis tracks the quantity of dollars traded.

Appreciation and Depreciation

Through most of 2022, the dollar surged against nearly every major currency on the planet. The euro fell below parity with the dollar for the first time in twenty years, meaning one dollar could purchase more than one euro. The Japanese yen weakened past 150 per dollar, a level not seen since 1990. The British pound, as noted, hit an all-time low. The dollar's strength was so pronounced that the DXY index, which tracks the dollar against a basket of six major currencies, climbed to its highest reading in two decades. This broad-based strengthening is appreciation: each dollar commands more foreign currency than before.

The math matters for trade. When the rate moves from 1.00 to 1.20 euros per dollar, a $100 American product that cost Europeans 100 euros now costs them 120 euros. U.S. exports get more expensive abroad, and foreign buyers purchase fewer of them. Simultaneously, a 100-euro German product drops from $100 to about $83 for American consumers. Imports get cheaper. Americans buy more.

Depreciation reverses every single effect. When the yen weakened past 150 per dollar in late 2022, Japanese-made cars, electronics, and machinery became a bargain for American buyers while dollar-priced American products became painfully expensive in Tokyo showrooms. A weaker currency boosts exports and raises the cost of imports, pushing net exports higher. This is why countries occasionally engage in competitive devaluation, deliberately weakening their currencies to gain a trade advantage, though the practice invites retaliation and is frowned upon by the IMF and WTO.

What Shifts Demand and Supply

Five forces drive exchange rate movements and appear repeatedly on the AP Macroeconomics exam. Each one operates through the demand curve, the supply curve, or both in the forex market.

Interest rate differentials. The Fed hiked rates aggressively throughout 2022 and 2023, pushing the federal funds rate from near-zero to above 5%, while the European Central Bank lagged months behind with smaller increases. Foreign investors chased the higher yields available on U.S. bonds and other dollar-denominated assets, creating a surge in demand for dollars. The dollar appreciated sharply against the euro, with the exchange rate moving from roughly 0.88 euros per dollar in early 2022 to above 1.03 by September. Interest rate differentials are the single most powerful short-run driver of exchange rate movements.

Relative income growth. If American GDP grows faster than Japan's, American households import more Japanese cars, electronics, and consumer goods. More dollars flow into the forex market as Americans exchange them for yen, shifting the supply of dollars rightward. The dollar depreciates. If Japan's economy booms instead, Japanese consumers import more American products, boosting demand for dollars and appreciating the dollar.

Inflation differentials. Higher U.S. inflation makes American exports pricier relative to foreign alternatives. Foreigners buy fewer American goods, shifting demand for dollars leftward. Meanwhile, Americans pivot to cheaper foreign imports, shifting the supply of dollars rightward. Both forces depreciate the dollar. The stagflation era of the 1970s, when U.S. inflation ran persistently above its trading partners, demonstrated this dynamic clearly as the dollar lost roughly half its value against the German mark between 1971 and 1979.

Speculation and expectations. Currency traders do not wait for published data. If markets expect the Fed to raise rates next month, traders buy dollars today, pushing up demand immediately and causing the appreciation they predicted. Self-fulfilling prophecy is baked into forex markets in a way that few other markets experience.

Tastes and preferences. A global surge in demand for American technology products increases foreign demand for dollars. A shift by American consumers toward European luxury goods increases the supply of dollars in the forex market. Preference shifts move curves, though they tend to operate more slowly than interest rate or speculation channels.

Exchange Rates and the Current Account

A strong dollar punishes American manufacturers, and the mechanism runs straight through net exports (NX = exports minus imports), a direct component of aggregate demand.

When the dollar appreciates, American goods cost more in foreign currency. Exports decline. Foreign goods cost fewer dollars. Imports climb. NX falls. During 2022, when the dollar reached two-decade highs, Caterpillar reported that unfavorable currency effects reduced its revenue by roughly $700 million. Procter & Gamble disclosed a $1.2 billion foreign exchange headwind. Multinational corporations with significant overseas revenue watched their earnings erode as the strong dollar made their foreign sales worth less when converted back to dollars.

Depreciation flips the entire dynamic. Exports become cheaper for foreign buyers, so export volume rises. Imports become more expensive for domestic consumers, so import volume falls. NX increases.

The connection to aggregate demand is direct. AD = C + I + G + NX. Dollar appreciation that lowers NX shifts aggregate demand leftward, a contractionary force. Dollar depreciation that raises NX shifts AD rightward, an expansionary force. The forex market is not some isolated corner of finance. Exchange rate swings feed straight into GDP through the net exports channel, and the AP exam tests this link relentlessly.

Exchange Rates and Capital Flows

The capital account (more precisely, the financial account) and the current account are two sides of one ledger. A country that imports more than it exports, running a current account deficit, must attract enough foreign investment to cover the gap, producing a capital account surplus. The United States has operated this way for decades: persistent trade deficits financed by massive foreign purchases of Treasury bonds, corporate equities, and American real estate.

The chain the AP exam tests more than almost anything else in this unit: interest rate to exchange rate to net exports. The Fed raises rates. Foreign investors chase higher yields and buy U.S. bonds. To make those purchases, they need dollars. Demand for dollars rises in the forex market. The dollar appreciates. A stronger dollar makes American exports expensive and imports cheap. Net exports fall.

That chain reveals a second channel of monetary policy that operates beyond domestic borders. When the Fed tightens, the obvious domestic effect is reduced investment from higher borrowing costs. The less obvious international effect: the dollar strengthens and net exports drop. Both channels are contractionary. They reinforce each other, amplifying the Fed's intended restraint on aggregate demand.

Reverse the chain for expansionary policy. The Fed cuts rates. The return on dollar assets falls. Foreign investors pull capital out or invest less. Demand for dollars weakens. The dollar depreciates. Exports rise, imports fall, and net exports increase. The domestic stimulus from cheaper borrowing gets amplified by the exchange rate channel. Two channels, same expansionary direction.

Worked Example

The Fed raises the federal funds rate from 3% to 5%.

Capital flows. U.S. bonds now yield 5% instead of 3%. A German pension fund managing 50 billion euros in assets notices the 300-basis-point spread between American and European bond yields. Money flows toward the higher return. Foreign investors compete to buy U.S. Treasuries, corporate bonds, and other dollar-denominated assets.

Forex market. To purchase U.S. bonds, foreign investors need dollars. Demand for dollars in the forex market shifts right. The exchange rate climbs from 0.90 to 1.05 euros per dollar.

Trade prices. A $100 American product that cost European buyers 90 euros now costs 105 euros. U.S. exports become significantly more expensive abroad. Meanwhile, European goods get cheaper for Americans. A 100-euro item that cost $111 now costs only about $95. Imports rise, exports fall.

Net exports and AD. Falling net exports reduce aggregate demand, reinforcing the contractionary effect of the rate hike through the domestic investment channel. The exchange rate channel and the investment channel both work in the same direction, tightening the economy.

The AP exam typically gives you one link in this chain and asks you to trace the rest. The sequence to internalize: interest rates up, capital inflows, dollar appreciates, net exports down, AD shifts left.