Supply and demand analysis is a useful tool for studying the short-run determination of the exchange rate. U.S. households and firms supply dollars to the foreign exchange market to acquire foreign currencies, which they need to purchase foreign goods, services, and assets. Foreigners demand dollars in the foreign exchange market to purchase U.S. goods, services, and assets. The market equilibrium exchange rate equates the quantities of dollars supplied and demanded in the foreign exchange market.
An increased preference for foreign goods, an increase in U.S. real GDP, an increase in the real interest rate on foreign assets, or a decrease in the real interest rate on U.S. assets will increase the supply of dollars on the foreign exchange market, lowering the value of the dollar. An increased preference for U.S. goods by foreigners, an increase in real GDP abroad, an increase in the real interest rate on U.S. assets, or a decrease in the real interest rate on foreign assets will increase the demand for dollars, raising the value of the dollar.
A tight monetary policy raises the real interest rate, increasing the demand for dollars, reducing the supply of dollars, and strengthening the dollar. A stronger dollar reinforces the effects of tight monetary policy on aggregate spending by reducing net exports, a component of aggregate demand. Conversely, an easy monetary policy lowers the real interest rate, weakening the dollar.