Exchange rates are determined by supply and demand in the foreign exchange market, where roughly $7.5 trillion changes hands each day.1Bank for International Settlements. OTC Foreign Exchange Turnover in April 2022 What drives that supply and demand is a mix of interest rates, inflation, economic output, trade balances, central bank policy, and investor psychology. How much any one of those factors actually moves a currency depends first on the exchange rate system the country operates under, because that decides how much room the market has to set the price at all.
The Exchange Rate System Sets the Rules
Before any economic factor can push a currency up or down, you have to know how much the country lets it move.
Under a free-floating system, supply and demand alone set the price. The United States, the eurozone, Japan, and most other large economies let their currencies trade this way.2Federal Reserve Bank of Minneapolis. Exchange Regimes: One Hand, the Other Hand, Both Hands Nobody guarantees a level, so prices swing when sentiment shifts. That volatility is the tradeoff for letting the currency adjust naturally to economic conditions.
Under a fixed or pegged system, a government or central bank locks its currency’s value to another currency or a basket weighted by trade and capital flows.3International Monetary Fund. Classification of Exchange Rate Arrangements and Monetary Policy Frameworks Holding the peg requires enough foreign reserves to buy or sell the home currency whenever the market pushes the rate off target. The payoff is predictability for cross-border business. The cost is that domestic monetary policy has to serve the peg first.
Most countries actually sit between the two extremes. In a managed float, the currency trades openly but the central bank steps in to smooth sharp moves or nudge the rate in a preferred direction.4NBER. Systematic Managed Floating China’s management of the renminbi and India’s periodic action on the rupee are well-known examples. The country gets some monetary independence and some exchange rate stability, but not the full benefit of either.
Interest Rates and Capital Flows
Interest rates are the single most-watched short-term driver. When a central bank raises its benchmark rate, assets in that currency offer higher yields, and foreign investors need to buy the currency to reach those returns.5Board of Governors of the Federal Reserve System. Monetary Policy and Exchange Rates During the Global Tightening That demand pushes the currency up. Rate cuts do the reverse.
The dynamic feeds a strategy called the carry trade: investors borrow in a low-rate currency, convert to a high-rate currency, and pocket the difference. When those trades stack up across billions of dollars, they amplify the rate effect. High-yielders get bid up further; low-yielders get sold off. That is why any headline hinting at a future rate change can move a currency more in an hour than a month of trade data.
Inflation and Purchasing Power
Inflation works as a slow drag. As domestic prices rise, each unit of the currency buys less, and investors look for alternatives. Countries with persistently high inflation tend to see their currencies weaken against countries with stable prices, because the real return on holding the currency erodes.6U.S. Bureau of Labor Statistics. How Currency Appreciation Can Impact Prices: The Rise of the U.S. Dollar
Interest rates and inflation pull against each other. A central bank might raise rates to attract capital, but if inflation is rising just as fast, the real yield (nominal rate minus inflation) hasn’t improved. Traders watch real rates for this reason.
Economists also use purchasing power parity, or PPP, to estimate where a rate “should” be based on the relative price of goods. If a basket costs $100 in the United States and ¥640 in Japan, PPP suggests roughly 6.4 yen per dollar.7Bank of Canada. Purchasing-Power Parity: Definition, Measurement, and Interpretation Market rates deviate from PPP constantly because productivity, capital flows, and trade barriers all get in the way. A currency trading below its PPP rate isn’t automatically undervalued; goods and services may simply be cheaper in that country. Still, large deviations can hint at eventual correction.
Economic Growth and Government Debt
Strong output attracts foreign investment. When GDP growth is solid and unemployment is low, investors expect higher corporate profits and better returns, and demand for the local currency rises. Weak growth sends capital elsewhere and the currency softens.
Debt matters too, though the relationship isn’t as clean as people assume. High debt-to-GDP ratios can erode confidence in a country’s long-term fiscal health, raising fears of eventual inflation or default. When confidence slips, borrowing costs rise and the currency weakens.8International Monetary Fund. Global Debt Remains Above 235% of World GDP But countries like Japan and the United States have carried enormous debt loads for decades without their currencies collapsing, largely because investors still trust their institutions and their ability to service that debt. Context weighs more than the raw number.
Balance of Trade
A country’s trade balance creates a structural current of supply and demand. When a country runs a trade surplus, foreign buyers need the exporter’s currency to pay for the goods, which supports the currency’s value. A persistent deficit works the other way: domestic consumers sell their own currency to buy foreign goods, adding supply to global markets and pushing the rate down.
The effect is real but slower than the interest rate channel, and there is a wrinkle. When a currency depreciates, you might expect the trade deficit to shrink immediately because exports just got cheaper for foreign buyers. In practice, the deficit often widens first, because existing import contracts are still priced at the old rate and export volumes take time to respond. Economists call this the J-curve effect, and the adjustment typically runs one to two years before improvement shows up in the data.
The United States is a partial exception to the usual story. Despite a trade deficit exceeding $900 billion in 2024, the dollar remains strong in part because so many global transactions are denominated in dollars regardless of whether the U.S. is involved.9Federal Reserve Bank of St. Louis. The U.S. Dollar’s Role as a Reserve Currency That structural demand offsets pressure a deficit of that size would normally create.
Central Bank Intervention
Central banks don’t only set interest rates. They have a full toolkit for managing a currency’s value, and they use it constantly, especially in managed-float systems.
The most direct tool is buying or selling foreign reserves. If a currency is falling too fast, the central bank sells its reserves of foreign currencies and buys its own, cutting supply and supporting the price. If the currency is climbing uncomfortably, the bank does the reverse.10Bank for International Settlements. Foreign Exchange Intervention and Financial Stability Effectiveness depends on whether markets believe the bank has enough reserves to keep going.
Quantitative easing works less directly. The central bank creates digital reserves to buy large quantities of government bonds, which pushes down long-term interest rates and tends to weaken the currency by making it less attractive to yield-seeking investors.11Bank of England. Quantitative Easing Tightening does the opposite. Raising benchmark rates or selling assets back into the market lifts rates, tightens liquidity, and strengthens the currency.12Federal Reserve. The Fed Explained – Monetary Policy The challenge is calibrating these tools so the exchange rate effect doesn’t undermine the domestic goals the policy is meant to serve.
Speculation, Sentiment, and Safe-Haven Flows
Most of the $7.5 trillion that trades daily has nothing to do with buying imported cars or paying overseas suppliers. Most of it is financial: banks hedging risk, funds betting on rate moves, and algorithms trading on millisecond price gaps.1Bank for International Settlements. OTC Foreign Exchange Turnover in April 2022 So rates are driven as much by expectations as by current fundamentals.
If enough traders believe a country’s economy is weakening, they sell the currency in anticipation, and the selling causes the decline they predicted. These self-fulfilling moves can push rates away from any model’s fair value for extended periods. It’s also why a single sentence from a Federal Reserve chair hinting at future cuts can move the dollar more in 30 minutes than a month of economic data.
Political stability sits in the same category and often overrides economic data. During wars, financial crises, or periods of severe uncertainty, investors rush toward currencies they consider safe stores of value. The U.S. dollar, the Swiss franc, and in some crises the Japanese yen have played that role. The effect can seem counterintuitive: the United States might be running huge deficits and facing domestic turmoil, yet the dollar still strengthens in a global crisis because investors are fleeing something worse. A country with solid fundamentals but an unstable government can see its currency plunge overnight on news of a coup or a contested election.
Why the Dollar Warps Every Other Rate
Any answer about exchange rate determination is incomplete without the dollar’s unusual position. As of the third quarter of 2025, U.S. dollar-denominated assets made up roughly 57% of global foreign exchange reserves.9Federal Reserve Bank of St. Louis. The U.S. Dollar’s Role as a Reserve Currency Oil, most commodities, and much of international trade are priced in dollars. Countries hold dollars not out of enthusiasm for U.S. fiscal policy but because they need them to participate in global commerce.
That structural demand acts as a floor under the dollar that other currencies don’t have. It also means changes in the dollar ripple outward to every other rate. When the Federal Reserve raises rates and the dollar strengthens, emerging-market countries that borrowed in dollars face bigger debt payments in their own currencies, which can trigger capital outflows and further depreciation. That feedback loop has sparked crises in Latin America, Southeast Asia, and elsewhere. Exchange rates aren’t a collection of independent pairs; they’re a network, and the dollar sits at the center of it.