Exchange Rates Explained: Appreciation, Depreciation, and the Forex Market

Exchange rates are the price of one currency measured in another, and they are set in the foreign exchange market (the forex market) by the supply of and demand for each currency. When demand for a currency rises or its supply falls, the currency appreciates (gains value); when demand falls or supply rises, it depreciates (loses value). This guide walks through the forex supply-and-demand graph, what shifts each curve, the difference between floating and fixed systems, and how currency moves feed back into exports, imports, and aggregate demand, which is exactly what AP Macro Unit 6 tests.

What an exchange rate actually measures

An exchange rate is simply the price of one country's money expressed in another country's money. If 1 US dollar trades for 0.90 euros, then the dollar-to-euro exchange rate is 0.90. Every exchange rate can be quoted two ways: dollars per euro or euros per dollar, and the two are reciprocals of each other. This matters on the exam because when the dollar gets stronger against the euro, the euro is automatically getting weaker against the dollar. One currency cannot appreciate without the other depreciating.

Two vocabulary words carry most of the unit. Appreciation means a currency has become more valuable, so it buys more of a foreign currency than before. Depreciation means a currency has become less valuable and buys less foreign currency. Under a market-driven system these changes happen continuously as buyers and sellers trade, so the forex market is best understood as an ordinary supply-and-demand market where the good being priced happens to be money itself.

The foreign exchange market: supply and demand for a currency

To draw the market for the US dollar, put the quantity of dollars on the horizontal axis and the exchange rate, meaning the price of a dollar measured in a foreign currency such as euros per dollar, on the vertical axis. The two curves are the demand for dollars and the supply of dollars, and where they cross sets the equilibrium exchange rate and the equilibrium quantity of dollars traded.

Demand for dollars comes from foreigners who need dollars to buy things priced in dollars. That includes buyers of US exports, tourists visiting the US, and investors purchasing US financial assets like Treasury bonds or stocks. The demand curve slopes downward: when the dollar is cheap (a low exchange rate), US goods and assets look like bargains, so foreigners want more dollars.

Supply of dollars comes from Americans who sell dollars to obtain foreign currency, because they want to buy imports, travel abroad, or invest in foreign assets. The supply curve slopes upward: when the dollar is strong (a high exchange rate), foreign goods and assets are cheap for Americans, so people supply more dollars to go get them. You can practice pushing these curves around in the interactive exchange rates sandbox, which is the fastest way to build intuition for which shift causes which result.

Reading the forex graph: appreciation and depreciation

On this graph, up means strong and down means weak. When the equilibrium exchange rate moves up the vertical axis, each dollar buys more foreign currency, so the dollar has appreciated. When equilibrium moves down, the dollar has depreciated. Two moves push the price up: an increase in demand for dollars (the demand curve shifts right) or a decrease in the supply of dollars (the supply curve shifts left). Two moves push the price down: a decrease in demand (demand shifts left) or an increase in supply (supply shifts right).

A clean exam habit is to graph one shift at a time, label the new equilibrium, and read the arrow. If demand for dollars increases, the demand curve shifts right, the intersection climbs, and the dollar appreciates while the quantity of dollars traded rises. If supply of dollars increases, the supply curve shifts right, the intersection falls, and the dollar depreciates while quantity again rises. Getting the curve labels and shift directions right is worth more points than any verbal explanation, so it is worth rehearsing on the graph walkthroughs until the moves are automatic.

What causes appreciation and depreciation

Five forces do almost all the work in AP Macro, and each one shifts demand, supply, or both. Notice that many of them act on both curves at once, which reinforces the direction of the currency move.

• Interest rates. If US interest rates rise relative to other countries, foreign investors want US bonds, so demand for dollars rises. At the same time Americans keep their money at home, so the supply of dollars falls. Both effects push the dollar up, so higher relative US interest rates cause the dollar to appreciate. This is the single most tested determinant because it links directly to monetary policy.
• Inflation. If US inflation is higher than abroad, US goods become expensive, foreigners buy fewer exports (demand for dollars falls), and Americans buy more foreign goods (supply of dollars rises). Higher relative US inflation causes the dollar to depreciate.
• Income (real GDP). On the AP model, faster US income growth raises imports, increases the supply of dollars, and depreciates the dollar (the trade-flow channel the exam tests). When foreign income grows, foreigners buy more US exports, demand for dollars rises, and the dollar appreciates.
• Tastes and preferences. If foreign consumers develop a stronger taste for US goods, demand for dollars rises and the dollar appreciates. If Americans crave foreign products, supply of dollars rises and the dollar depreciates.
• Speculation and expectations. If investors expect the dollar to be worth more soon, they buy dollars now to profit later, which raises demand today and appreciates the dollar immediately. Expectations can move currencies before any real-economy change occurs.

Determinants at a glance

Floating versus fixed exchange rates

A floating exchange rate is set entirely by market supply and demand, with no government target. Most major currencies, including the dollar, euro, and yen, float, so their values drift up and down continuously as the determinants above shift the curves. A fixed (pegged) exchange rate is a rate a government commits to hold at a chosen level, usually against a major currency. To keep a peg, the central bank must intervene: if the market would push the currency below the peg, the bank buys its own currency using foreign-currency reserves to prop demand up; if the market would push it above the peg, the bank sells its own currency to add supply. A managed float sits in between, mostly market-driven but with occasional intervention. If you want the head-to-head tradeoffs, compare floating vs. fixed exchange rates directly.

The tradeoff is stability versus flexibility. A fixed rate gives traders and investors predictability, but defending it can drain reserves and ties the central bank's hands, because it must prioritize the peg over domestic goals like fighting unemployment. A floating rate lets monetary policy focus on the domestic economy and self-corrects trade imbalances over time, but it exposes businesses to day-to-day currency swings.

How exchange rates affect exports and imports

Currency value flows straight into trade, and this is where forex connects to the rest of macro. When the dollar appreciates, US goods cost more in foreign currency, so exports fall, while foreign goods cost less in dollars, so imports rise. Net exports (exports minus imports) therefore decrease. Because net exports are a component of aggregate demand, dollar appreciation shifts US aggregate demand to the left, which is contractionary.

When the dollar depreciates, the story reverses: US exports get cheaper abroad and rise, imports get more expensive and fall, net exports increase, and aggregate demand shifts right, which is expansionary. A memory hook that avoids the classic mistake: a strong currency is bad for exporters, and a weak currency is bad for importers and travelers. The counterintuitive part for students is that a strong dollar is not automatically good for the economy, since it widens the trade deficit by making the country's own products less competitive abroad.

Tying it together and where to practice

The whole unit reduces to one chain. A determinant shifts the demand or supply of a currency, which appreciates or depreciates that currency, which changes exports and imports in the opposite intuitive direction for exports, which changes net exports and therefore aggregate demand. If you can narrate that chain and draw the matching forex graph with correctly labeled curves and shift arrows, you can answer almost any Unit 6 free-response or multiple-choice question.

The most reliable way to lock it in is repetition with immediate feedback. Reshift the curves yourself in the forex sandbox, review the broader unit in the AP Macro course hub, and rehearse drawing the graph under exam conditions with the graph walkthroughs. Once the graph moves feel automatic, the vocabulary and trade effects follow from it rather than needing to be memorized separately.