In AP Macro (Topic 6.3), the supply of a currency is the quantity of that currency offered in the foreign exchange market, arising when people trade it away to make payments in other currencies, and it shows a positive relationship between the exchange rate and quantity supplied.
The supply of a currency is where that currency comes from in the foreign exchange market. Here's the intuition that makes it click: a country's own residents supply their currency. When Americans buy Japanese cars, French vacations, or German bonds, they have to trade dollars away to get yen, euros, or other currencies. Every one of those transactions puts dollars onto the forex market. So the supply of dollars comes from Americans buying foreign stuff, not from foreigners.
Per the CED (6.3.A), the supply of a currency arises from making payments in other currencies, and the supply curve slopes upward. When the dollar appreciates (the exchange rate rises), foreign goods become cheaper for Americans, so Americans buy more imports and supply more dollars to pay for them. That's the positive relationship between the exchange rate and the quantity supplied. Important warning up front: this is NOT the same thing as the money supply from Unit 4. The money supply is the total stock of money in the domestic economy. The supply of a currency is just the amount being offered for trade in the forex market at each exchange rate.
This term lives in Unit 6 (Open Economy: International Trade and Finance), Topic 6.3, and it's half of the foreign exchange market model. Learning objective 6.3.A asks you to define the forex market, demand for currency, and supply of currency, while 6.3.B and 6.3.C require you to graph equilibrium exchange rates and show how shifts in supply or demand move the exchange rate back to equilibrium. If you can't identify what shifts currency supply (changes in imports, capital outflows, relative interest rates), you can't draw the forex graph correctly, and that graph is one of the most reliably tested models in Unit 6. It also connects backward to monetary policy, since expansionary policy lowers interest rates, pushes investors toward foreign assets, increases the supply of the domestic currency, and depreciates it.
Keep studying AP Macroeconomics Unit 6
Demand for a currency (Unit 6)
Supply and demand for a currency are mirror images. Foreigners buying U.S. goods and assets demand dollars, while Americans buying foreign goods and assets supply dollars. Here's the elegant part: the supply of dollars is literally the demand for some other currency. Every forex transaction is both at once.
Exchange Rate (Unit 6)
The exchange rate is the price determined where currency supply meets currency demand. An increase in the supply of dollars (say, Americans importing more) pushes the dollar's value down, which is depreciation. The exchange rate is the y-axis of the graph this term shifts.
Monetary Policy (Unit 4)
This is the big cross-unit chain the exam loves. Expansionary monetary policy lowers domestic interest rates, so investors sell domestic assets to chase higher returns abroad. To buy foreign assets they must supply the domestic currency on the forex market, which depreciates it. One Fed move ripples all the way to the exchange rate.
Money Supply (Unit 4)
These sound identical but live on different graphs. The money supply is the vertical line in the money market showing the total stock of money in the economy. The supply of a currency is the upward-sloping curve in the forex market showing how much currency gets offered for trade at each exchange rate. A bigger money supply can indirectly increase currency supply (via lower interest rates), but they are separate models.
Topic 6.3 shows up heavily in multiple choice and in Unit 6 FRQs that ask you to draw a correctly labeled foreign exchange market graph. Typical MCQ stems mirror what you'll see in practice: which factor directly affects the supply of a currency, what happens to currency supply when a country increases imports (it increases, since residents need foreign currency to pay for them), or what happens to the exchange rate when both demand and supply increase but supply increases more (the currency depreciates). On FRQs, expect to draw the dollar market with the exchange rate on the vertical axis, shift the supply curve in response to a scenario like rising imports or capital outflow, and state whether the currency appreciates or depreciates. The two skills you must nail are (1) knowing that the country's own residents supply its currency and (2) shifting the curve the right direction and reading off the new equilibrium per 6.3.B and 6.3.C.
The money supply (Unit 4) is the total stock of money in the domestic economy, drawn as a vertical line in the money market and controlled by the central bank. The supply of a currency (Unit 6) is the amount of that currency offered for exchange in the forex market, drawn as an upward-sloping curve, and it comes from residents making payments in foreign currencies. If a question mentions exchange rates or the forex market, it wants currency supply. If it mentions interest rates and the money market, it wants money supply.
A country's own residents supply its currency, because they must trade it away to pay for foreign goods, services, and financial assets.
The supply curve for a currency slopes upward, since a higher exchange rate makes imports cheaper, leading residents to buy more from abroad and supply more currency.
Anything that increases imports or capital outflow (like lower domestic interest rates) shifts the supply of the currency right and causes depreciation.
Supply of a currency is not the money supply; one is a forex market curve, the other is the domestic stock of money from Unit 4.
Equilibrium in the forex market happens where quantity demanded equals quantity supplied of the currency, and surpluses or shortages push the exchange rate back toward that point.
If both demand and supply of a currency rise but supply rises more, the currency depreciates.
It's the quantity of a currency offered in the foreign exchange market, which arises when that country's residents make payments in other currencies. Per CED 6.3.A, it shows a positive relationship between the exchange rate and quantity supplied.
No. The money supply is the total stock of money in the domestic economy (Unit 4, money market, vertical curve). The supply of a currency is the amount offered for trade in the forex market (Unit 6, upward-sloping curve). The AP exam tests them on completely different graphs.
The country's own residents. When Americans buy Japanese imports or European bonds, they supply dollars to the forex market to get the foreign currency they need. Foreigners are the ones who demand dollars.
It increases. More imports means residents need more foreign currency to pay for them, so they supply more of their own currency on the forex market, which shifts supply right and depreciates the currency.
When the dollar appreciates, foreign goods get cheaper for Americans, so they import more and need to trade away more dollars to pay for those imports. Higher exchange rate, higher quantity of dollars supplied. That's the positive relationship in CED 6.3.A.