The Foreign Exchange Market

AP Macroeconomics· AP Macroeconomics CED — Open Economy: International Trade and Finance· 14 min read

1. 1. What Is The Foreign Exchange Market?★☆☆☆☆⏱ 2 min

The foreign exchange market (shortened to forex or FX market) is the decentralized global market where national currencies are bought and sold, enabling international trade, investment, and cross-border financial transactions. For AP Macroeconomics, we model this market as a standard competitive supply and demand market for a specific currency, where the "price" of that currency is its exchange rate relative to another currency. The full open economy unit makes up 12-16% of total AP exam score, with the foreign exchange market comprising approximately 4-6% of the total exam.

📘 Definition

Nominal Exchange Rate

e

The amount of domestic currency required to buy one unit of foreign currency, per standard AP Macroeconomics notation.

Example:

$e = 1.08$ USD/EUR means 1 euro costs 1.08 US dollars.

2. 2. Currency Appreciation and Depreciation★★☆☆☆⏱ 3 min

Currency appreciation occurs when a currency becomes more valuable relative to another currency, meaning it can buy more of the foreign currency. Currency depreciation occurs when a currency becomes less valuable, meaning it buys less of the foreign currency. For AP calculations, we measure the magnitude of appreciation or depreciation using percentage change, using the formula below:

\% \Delta e = \frac{e_{\text{new}} - e_{\text{old}}}{e_{\text{old}}} \times 100\%

A positive percentage change means the foreign currency has appreciated, because it now costs more domestic currency to buy one unit of foreign currency. By definition, if foreign currency appreciates, domestic currency must depreciate, and vice versa. This inverse relationship is the most important thing to remember when working with exchange rate changes.

📐 Worked Example

Suppose from the perspective of a US-based observer, 1 British pound (GBP, foreign currency) initially costs 1.25 USD. One year later, 1 GBP costs 1.40 USD. (a) Calculate the percentage change in the GBP exchange rate, and (b) state whether USD appreciated or depreciated relative to GBP.

1
We use standard notation: $e$ = USD per GBP, so $e_{old} = 1.25$ and $e_{new} = 1.40$ .
2
Substitute into the percentage change formula:
3
$\frac{1.40 - 1.25}{1.25} \times 100\% = \frac{0.15}{1.25} \times 100\% = 12\%$
4
A positive 12% change in $e$ means GBP now costs 12% more USD than it did a year ago, so GBP has appreciated by 12% relative to USD.
5
Since GBP appreciated, USD can buy fewer GBP than before, so USD has depreciated relative to GBP.

Exam tip:

Always label your exchange rate with 'X per Y' before starting any calculation. If you leave it unlabeled, you will almost always mix up which currency appreciated, which is the most common wrong answer on AP MCQs.

3. 3. Supply and Demand in the Flexible Exchange Rate Market★★☆☆☆⏱ 3 min

A flexible (or floating) exchange rate system is one where the exchange rate is determined entirely by market forces, with no intentional central bank intervention to fix the rate at a specific level. This is the default model for the AP exam unless the question explicitly states the country has a fixed exchange rate.

For any given currency, demand for the currency comes from foreigners who want to buy the country’s exports, goods, services, or financial assets: they must buy the domestic currency to complete these transactions. Demand is downward sloping because a cheaper domestic currency means foreigners can buy more domestic currency for the same amount of their own currency, increasing quantity demanded.

Supply of the domestic currency comes from domestic residents who want to buy foreign goods, services, or assets: they must sell their domestic currency to get foreign currency. Supply is upward sloping because a more valuable domestic currency means domestic residents get more foreign currency per unit of domestic currency, increasing quantity supplied. Equilibrium occurs at the intersection of supply and demand, where quantity of the currency demanded equals quantity supplied.

📐 Worked Example

China increases its demand for US agricultural exports. Assuming a flexible exchange rate, show how this affects the market for US dollars (USD) and what happens to the value of USD relative to Chinese yuan (CNY).

1
Set up a correctly labeled graph: x-axis = Quantity of USD, y-axis = Exchange rate (CNY per USD). Draw downward-sloping initial demand $D_{1}$ and upward-sloping initial supply $S_{1}$ , with equilibrium exchange rate $e_{1}$ at their intersection.
2
Increased Chinese demand for US exports means Chinese consumers and importers need more USD to buy US goods, so demand for USD shifts right to $D_{2}$ .
3
No factor has changed US demand for Chinese goods, so supply of USD remains unchanged at $S_{1}$ .
4
The new intersection of $S_{1}$ and $D_{2}$ occurs at a higher equilibrium exchange rate $e_{2} > e_{1}$ .
5
Since $e_{2}$ is CNY per USD, a higher $e_{2}$ means one USD buys more CNY, so USD has appreciated relative to CNY.

Exam tip:

When drawing the FX market for a specific currency, always put that currency on the x-axis (quantity) and its price (other currency per that currency) on the y-axis. Flipping the axes will always lead to wrong shift conclusions.

4. 4. Key Determinants of Exchange Rate Shifts★★★☆☆⏱ 3 min

All exchange rate changes in a flexible system come from shifts in supply or demand for a currency, and AP exam questions almost always test your ability to connect a given economic change to the correct shift and outcome. The most commonly tested determinants are:

Tastes/Preferences for Goods: Increased foreign demand for domestic exports shifts demand right → domestic currency appreciates; increased domestic demand for foreign imports shifts supply right → domestic currency depreciates.
Relative Price Levels: If domestic inflation is higher than foreign inflation, domestic goods become more expensive, so foreign demand for exports falls (demand shifts left) and domestic demand for imports rises (supply shifts right) → domestic currency depreciates.
Relative Real Interest Rates: Higher domestic real interest rates attract foreign investment, so demand for domestic currency shifts right and supply shifts left → domestic currency appreciates. This is the most frequently tested determinant, often paired with monetary policy questions.
Relative Income Growth: Faster domestic income growth increases demand for imports, so supply of domestic currency shifts right → domestic currency depreciates.
Political/Economic Risk: Higher domestic risk causes investors to pull capital out, so demand shifts left and supply shifts right → domestic currency depreciates.

📐 Worked Example

Sweden undertakes expansionary fiscal policy that raises Swedish real interest rates relative to real interest rates in Norway. All else equal, what happens to the value of the Swedish krona (SEK) relative to the Norwegian krone (NOK)?

1
Higher Swedish real interest rates mean Swedish assets offer higher returns than comparable Norwegian assets, all else equal.
2
Norwegian investors want to buy more Swedish assets to earn higher returns, so they need to buy SEK, increasing demand for SEK.
3
Swedish investors have less incentive to invest in lower-yielding Norwegian assets, so they supply less SEK to buy NOK, decreasing supply of SEK.
4
A right shift in demand and left shift in supply for SEK both increase the equilibrium exchange rate (NOK per SEK), so SEK appreciates relative to NOK.

Exam tip:

If a question mentions a change in real interest rates, the rule of thumb is: higher relative rates → currency appreciates, lower relative rates → currency depreciates. This holds 99% of the time on the AP exam.

5. 5. Purchasing Power Parity★★★☆☆⏱ 3 min

Purchasing Power Parity (PPP) is a long-run theory of exchange rate determination that states exchange rates adjust to equalize the purchasing power of different currencies, meaning identical goods should cost the same in both countries when converted to a common currency. It is built on the law of one price, which states that identical goods should have the same price everywhere after accounting for exchange rates.

e^{PPP} = \frac{P_d}{P_f}

Where $P_{d}$ is the domestic price of an identical good/basket of goods, and $P_{f}$ is the foreign price of the same good/basket. PPP does not hold exactly in the short run due to trade barriers, non-traded goods, and different consumption baskets, but it is a useful benchmark for long-run exchange rate trends.

📐 Worked Example

An identical basket of consumer goods costs 4000 CAD in Canada and 2500 GBP in the United Kingdom. What is the PPP equilibrium CAD per GBP exchange rate? If the actual market exchange rate is 1.5 CAD per GBP, is CAD overvalued or undervalued relative to PPP?

1
We define $e^{P P P}$ as CAD per GBP, so $P_{d} = 4000$ CAD, $P_{f} = 2500$ GBP.
2
Apply the PPP formula:
3
$e^{PPP} = 4000 / 2500 = 1.6 \text{ CAD per GBP}$
4
The actual exchange rate is 1.5 CAD per GBP, which is lower than the PPP rate. This means GBP costs less CAD than the PPP benchmark, so GBP is undervalued.
5
If GBP is undervalued, CAD must be overvalued relative to its PPP equilibrium value: each CAD buys more GBP at the market rate than it would at PPP.

Exam tip:

To check for over/undervaluation: if actual $e$ (domestic per foreign) > $e^{P P P}$ , foreign currency is overvalued and domestic is undervalued, and vice versa.

6. Common Pitfalls

Wrong move:

When $e$ is defined as USD per EUR, you conclude an increase in $e$ means USD appreciated.

Why:

Students mix up which currency the exchange rate is pricing, confusing 'number of USD per EUR' with 'number of EUR per USD'.

Correct move:

Always label $e$ as [price currency] per [priced currency], so $e$ is the price of the priced currency. An increase in $e$ means the priced currency has appreciated.

Wrong move:

When drawing the FX market for USD, you put quantity of foreign currency on the x-axis.

Why:

Students get confused about which currency the market is for, leading to flipped shift conclusions.

Correct move:

The FX market for X always has quantity of X on the x-axis, price of X (Y per X) on the y-axis, where Y is the other currency.

Wrong move:

Higher domestic interest rates cause the domestic currency to depreciate.

Why:

Students confuse the effect of higher nominal interest rates from inflation with the ceteris paribus effect of higher real interest rates.

Correct move:

Always separate nominal vs real: all else equal, higher relative real interest rates attract foreign investment, so domestic currency appreciates.

Wrong move:

An increase in domestic income leads to domestic currency appreciation because higher income means more demand for domestic goods.

Why:

Students forget that higher domestic income increases demand for imports, which changes the supply of domestic currency.

Correct move:

All else equal, higher domestic income relative to foreign income increases domestic demand for imports, leading domestic residents to supply more domestic currency, so domestic currency depreciates.

Wrong move:

You calculate the PPP exchange rate as $P_{f} / P_{d}$ instead of $P_{d} / P_{f}$ .

Why:

Students mix up the definition of $e$ as domestic per foreign.

Correct move:

Remember that $e = P_{d} / P_{f}$ for $e$ = domestic per foreign, which aligns with the logic that if domestic prices double, you need twice as much domestic to buy the same foreign good.

7. Quick Reference Cheatsheet

Category	Formula / Rule	Notes
Nominal Exchange Rate Definition	$e = \frac{Domestic Currency}{Foreign Currency}$	Standard AP notation; $e$ is price of 1 unit of foreign currency
Percentage Change in Exchange Rate	$%Δ e = \frac{e _{n e w} - e _{o l d}}{e _{o l d}} \times 100%$	Positive Δe = foreign currency appreciates, domestic depreciates
PPP Equilibrium Exchange Rate	$e^{P P P} = \frac{P _{d}}{P _{f}}$	$P_{d}$ = domestic price, $P_{f}$ = foreign price, $e^{P P P}$ = domestic per foreign
Relative Real Interest Rate Rule	Higher domestic real rates → domestic currency appreciates	Most frequently tested shift determinant on AP exam
FX Market Graph Rule	X-axis = Quantity of [priced currency], Y-axis = [other currency] per [priced currency]	Flipping axes leads to wrong shift conclusions
Over/Undervaluation Rule	Actual $e$ > $e^{P P P}$ : foreign currency overvalued	Inverse: actual $e$ < $e^{P P P}$ : foreign currency undervalued

When this came up on past exams

AI-estimated based on syllabus patterns — cross-check with official past papers for accuracy. Use only as revision-focus signals.

2023 · MCQ
Exchange rate shift from interest rate change
2022 · FRQ
FX market graph and PPP calculation
2021 · MCQ
Identify appreciation from exchange rate change

What's Next

Mastery of the foreign exchange market is critical for analyzing open economy macroeconomics, a heavily tested section on the AP Macroeconomics exam. Next, you will connect foreign exchange rate changes to broader macroeconomic outcomes like net exports, aggregate demand, and economic growth, building on the supply-demand framework you learned here. Understanding how exchange rate changes impact trade balances also prepares you to analyze policy interventions like currency manipulation and fixed exchange rate systems, which are common topics in long free-response questions. This foundation will help you work through complex problems that combine balance of payments accounts, monetary policy, and exchange rate dynamics.