Why Currency Exchange Rates Change

A currency's value is not set by any single authority. It is the running output of a market where roughly $7.5 trillion changes hands every day, according to the Bank for International Settlements' 2022 Triennial Central Bank Survey, more than the daily volume of every stock and bond market on Earth combined. What moves that price is a small set of well-documented forces: interest rate differentials, trade and capital flows, inflation expectations, and occasional central bank intervention. This article explains the mechanism, not where any currency is headed next.

Currencies are prices, and prices come from supply and demand

An exchange rate is a ratio, not a price in the sense that a loaf of bread has a price. When EUR/USD quotes at 1.08, it means one euro currently trades for 1.08 US dollars. Because it is a ratio between two things, a move can originate on either side: the euro can strengthen, the dollar can weaken, or both can shift at once in ways that partly offset or reinforce each other.

That ratio is set the same way any freely traded asset's price is set: by the balance of buy and sell orders in a market. Foreign exchange, often called forex or FX — the global marketplace where one country's currency is exchanged for another's — is decentralized. There is no single exchange building or opening bell. Instead, it runs continuously across a network of banks, brokers, corporations, central banks, and electronic trading platforms spanning every major time zone, opening in Wellington and Sydney, moving through Tokyo, Singapore, and Hong Kong, then London, then New York, before starting again.

Every transaction in that network, an exporter converting euros back into yen, a pension fund rebalancing into foreign bonds, a tourist buying pesos at an airport kiosk, adds a small data point to the supply-and-demand ledger that produces the quoted rate. No individual trade moves the rate meaningfully. What moves it is when large numbers of participants shift their behavior in the same direction at once, usually because something changed about the relative attractiveness of holding one currency versus another.

That "relative attractiveness" question is really the whole story. Investors, companies, and governments are constantly deciding whether it is more useful to hold dollars, euros, yen, or renminbi at this moment, and that decision rests on a handful of measurable factors: what return each currency earns you, what it will buy you, and how much political and economic risk comes attached to holding it. The rest of this article works through each of those factors individually, because they operate on different time horizons and don't always point the same direction at once.

Interest rate differentials: the dominant short-term driver

Ask most economists what moves exchange rates week to week, and the answer starts with interest rates. When a country's central bank raises its policy rate while another holds steady, the first country's government bonds and bank deposits suddenly offer a better return for the same level of perceived safety. Global capital, always searching for the best risk-adjusted yield, flows toward that currency to capture the higher rate. To do that, investors first have to sell their existing currency and buy the one paying more, and that buying pressure is what pushes the exchange rate.

This relationship has a name in economics: uncovered interest rate parity, the theory that expected currency returns should equalize across countries once interest rate differences are accounted for. In practice, the theory holds only loosely and imperfectly over short horizons, a point researchers have documented extensively since the 1980s (the persistent gap between what the theory predicts and what actually happens is sometimes called the "forward premium puzzle"), but the underlying direction of the effect, higher relative rates attracting capital and supporting a currency, is one of the more consistently observed patterns in currency markets.

A related and closely watched mechanism is the carry trade: a strategy where investors borrow in a currency with a low interest rate and invest the proceeds in assets denominated in a currency with a higher interest rate, pocketing the rate difference (the "carry") as long as the exchange rate does not move against them enough to erase the gain. The Japanese yen has historically been a common funding currency for carry trades because Japan held near-zero interest rates for an extended period; when Japan's rates moved and expectations shifted, unwinding carry positions could itself become a source of sharp yen appreciation, since traders needed to buy back yen to repay what they had borrowed. Carry trades illustrate why interest rate differentials matter so much: they create a direct, ongoing financial incentive to move capital from one currency into another, and that incentive updates continuously as central banks adjust policy or as market expectations about future policy shift.

The global foreign exchange market trades roughly $7.5 trillion per day, according to the Bank for International Settlements' 2022 Triennial Central Bank Survey — larger than the world's equity and bond markets' daily trading volumes combined, and up from $6.6 trillion three years earlier.

How do interest rates affect exchange rates?

Higher interest rates make a currency's government bonds and bank deposits more attractive to global investors seeking yield, which increases demand for that currency relative to others with lower rates and tends to push its value up. This dynamic, formalized as interest rate parity, is one of the most consistently observed short-to-medium-term drivers of exchange-rate movement, though it interacts with expectations, risk appetite, and capital controls in ways that can complicate the simple relationship.

Markets price in the future, not just the present

Currency markets are forward-looking, which means rates often move on anticipated events rather than the events themselves. If traders broadly expect a central bank to cut interest rates at its next meeting, the currency can weaken in the days or weeks leading up to that meeting, well before any announcement, because the market is already incorporating the expected change into today's price. By the time the actual decision is announced, much of the anticipated move may already be reflected in the rate, and the currency can even move in the opposite direction if the actual decision differs from what was priced in, a pattern traders sometimes describe as "buy the rumor, sell the news."

This works the same way a stock price can fall after an earnings report even when the company beat its current-quarter numbers, if management's forward guidance disappoints. The market was never pricing last quarter; it was pricing the trajectory. A single sentence in a central bank press conference that hints at a policy shift, sometimes called "forward guidance," can move a currency more in an afternoon than an actual rate change that had already been fully anticipated weeks in advance.

This forward-looking behavior is why financial journalists frequently attribute currency moves to statements rather than actions: a central bank governor's choice of the word "patient" versus "vigilant" in a press conference can shift billions of dollars in trading positions within minutes, because traders are parsing the statement for clues about the path of future policy, not just the decision already announced that day.

Why does a currency sometimes move before a central bank announcement?

Because currency markets price in expected policy changes ahead of time rather than waiting for them to happen. Traders position based on economic data, speeches, and historical patterns that suggest where policy is heading, so the exchange rate often reflects the anticipated decision well before the central bank makes it official.

Trade balances and capital flows shape the medium-term trend

Beneath the interest-rate-driven noise of daily trading sits a slower, more structural force: the flow of a country's currency required to pay for trade and cross-border investment. A country that imports more goods and services than it exports runs a trade deficit, and to pay foreign suppliers, importers must sell their own currency to buy the supplier's currency, which increases the domestic currency's supply on the open market. All else equal, more supply relative to demand pushes a currency's value down over time.

The reverse holds for a country running a persistent trade surplus. Japan's large and sustained trade surpluses through much of the late twentieth century created a structural tailwind for the yen, as foreign buyers of Japanese goods continuously needed yen to complete those purchases. The United States, by contrast, has run persistent trade deficits for decades, a structural headwind for the dollar in isolation, though the dollar's role as the world's primary reserve currency, the currency central banks and institutions hold as their main store of international value, has offset much of that pressure by keeping foreign demand for dollar-denominated assets elevated regardless of the trade balance.

Capital flows add a second layer on top of trade flows. Foreign direct investment, portfolio investment into stocks and bonds, and cross-border corporate acquisitions all require converting one currency into another, and the scale of these flows now dwarfs pure trade-related currency demand in most developed economies. A large foreign acquisition of a domestic company, for instance, requires the acquirer to sell its own currency and buy the target country's currency to fund the deal, creating temporary but sometimes sizable demand for that currency.

Purchasing power parity: the long-run anchor, with real limits

Over years and decades, a different force dominates: inflation differentials, formalized in economics as purchasing power parity (PPP) — the theory that exchange rates should adjust over time so that identical goods and services cost roughly the same amount once converted into a common currency. If Country A's inflation rate consistently runs several percentage points higher than Country B's, PPP predicts Country A's currency needs to depreciate against Country B's by a similar margin each year, or else Country A's goods become steadily more expensive relative to Country B's in international terms, which would be unsustainable for trade competitiveness.

PPP is a genuinely useful long-run anchor, and it is one of the most extensively studied relationships in international economics, but it comes with well-documented caveats that matter for anyone trying to use it. First, PPP holds poorly, sometimes not at all, over short time horizons: exchange rates can and do deviate from what PPP would predict for years at a stretch, because interest rate differentials, capital flows, and risk sentiment dominate short-term pricing. Second, PPP assumes goods are freely tradable and comparable across borders, but many goods and services (housing, haircuts, restaurant meals, healthcare) are not traded internationally at all, so their prices can diverge indefinitely without triggering the currency adjustment PPP predicts. Third, transportation costs, tariffs, taxes, and differences in consumer preferences all create persistent gaps between what a strict PPP model expects and what actually happens.

Economists commonly distinguish between absolute PPP, the strict claim that a basket of goods should cost exactly the same in any two countries once converted to a common currency, and relative PPP, the weaker and more empirically supported claim that changes in the exchange rate over time should track the difference in the two countries' inflation rates. Relative PPP holds up considerably better in long-run data than absolute PPP does, which is part of why economists lean on it as a multi-year trend indicator rather than a precise short-term forecasting tool.

This is why currencies in economies with persistently high inflation, historically including Argentina and Turkey over extended periods, have depreciated sharply against lower-inflation currencies like the dollar or euro across long stretches of time, even when short-term capital flows occasionally pushed the other direction for weeks or months at a time. The pattern is consistent with PPP's core logic: a currency that keeps losing domestic purchasing power to inflation eventually loses external purchasing power too.

Regime type	How the rate is set	Who intervenes, and how	Real-world example
Free-floating	Determined entirely by market supply and demand, no target level	Central bank rarely intervenes directly; may use interest rates to influence conditions	US dollar, euro, Japanese yen, British pound
Managed float	Mostly market-determined, but the central bank intervenes occasionally to smooth volatility or resist rapid moves	Buys or sells its own currency at its discretion, no fixed target	Indian rupee, Chinese renminbi's daily trading band around a set reference rate
Fixed / pegged	Officially tied to another currency or basket at a set rate, defended by the central bank	Central bank continuously buys or sells to hold the peg, using foreign reserves	Hong Kong dollar (pegged to the US dollar since 1983), Danish krone (pegged to the euro)
Currency board / dollarization	No independent currency at all, or a currency fully backed 1:1 by a reserve currency	No monetary policy independence; money supply directly tied to reserve holdings	Ecuador and El Salvador use the US dollar as legal tender

Exchange rate regimes sit on a spectrum from fully market-determined to fully fixed, and each trades off flexibility against stability differently.

Does inflation affect exchange rates?

Yes, primarily over the long run. Purchasing power parity predicts that a country with persistently higher inflation than its trading partners will see its currency depreciate against theirs over time, to keep the relative cost of goods roughly stable. Over short periods, interest rate differentials and capital flows typically dominate, and PPP-based predictions can be wrong for extended stretches before eventually reasserting themselves.

Central bank intervention and the legacy of Bretton Woods

Most of the world's heavily traded currencies today, including the US dollar, the euro, the Japanese yen, and the British pound, are free-floating, meaning their exchange rates are set by market supply and demand rather than fixed by any government. That was not always the arrangement. From 1944 until the early 1970s, the major industrial economies operated under the Bretton Woods system, an international monetary arrangement established at a conference in Bretton Woods, New Hampshire, that pegged participating currencies to the US dollar at fixed rates, while the dollar itself was pegged to gold at $35 per ounce, with the US government committing to redeem dollars for gold at that rate on demand from foreign governments.

That system ended on August 15, 1971, when US President Richard Nixon announced the United States would suspend the dollar's convertibility into gold, a decision historians and economists refer to as the Nixon Shock. Rising US inflation, mounting government spending, and a growing gap between the dollar's fixed gold value and the actual amount of dollars circulating internationally had made the peg increasingly difficult to defend, and foreign governments were increasingly exercising their right to redeem dollars for gold, straining US gold reserves (Federal Reserve History, Federal Reserve Bank of St. Louis). Within the following months, major currencies began floating against the dollar rather than holding a fixed peg, and by 1973 most major economies had formally shifted to the floating-rate system that persists today.

Not every currency floats freely even now. Some countries choose a pegged or fixed exchange rate, tying their currency's value to another currency, usually the dollar or euro, at a set rate that the central bank actively defends by buying or selling its own currency in the market. The Hong Kong dollar has been pegged to the US dollar within a narrow band since 1983, and the Hong Kong Monetary Authority intervenes whenever the market rate threatens to move outside that band. Other countries operate a managed float, letting the market set the rate day to day while the central bank occasionally intervenes to smooth out volatility or resist moves it considers excessive, without committing to defend a specific fixed level. China's renminbi operates under a managed system where the central bank sets a daily reference rate and allows trading within a band around it.

Direct central bank intervention on freely floating currencies, actually buying or selling large volumes of a currency to move its price, is comparatively rare among major economies today, because sustained intervention against fundamental market forces has historically proven difficult and expensive to maintain, as the Bretton Woods experience itself demonstrated. When it happens, it is usually to counter what policymakers view as excessive short-term volatility or a rate that has become disconnected from underlying fundamentals, rather than an attempt to fix a currency at a specific target indefinitely.

Common misconceptions about currency movements

A frequent assumption is that a "strong" currency is unambiguously good for an economy and a "weak" one is unambiguously bad. In reality, the effects cut in opposite directions depending on which part of the economy you look at. A weaker currency makes a country's exports cheaper for foreign buyers, which can support manufacturing, agriculture, and tourism industries, while a stronger currency benefits consumers and businesses buying imported goods and raw materials but can make exporters less competitive abroad. Which effect matters more for a given country's overall economic health depends heavily on how much of that economy is export-driven versus import-dependent, and there is no universal answer that applies equally to every country.

A second misconception is that central banks set exchange rates the way a store sets a price tag. As covered above, most major currencies float freely, with the market, not any government body, determining the rate through the aggregate of supply and demand across millions of daily transactions. Central banks influence currency values indirectly, primarily through interest rate policy, and occasionally through direct intervention, but for a floating currency they do not fix the number outright, and the market can and does move exchange rates against a central bank's stated preferences.

A third common error is attributing a single day's currency move entirely to one headline or news event. Exchange rates reflect the combined effect of thousands of simultaneous inputs: interest rate expectations, trade data releases, geopolitical developments, commodity price shifts, and speculative positioning among large institutional traders. A financial news headline attributing a currency's daily move to a single cause is usually offering a simplified narrative for a genuinely multi-causal process, and the same headline event can coincide with several other factors moving in the same direction at once, making it difficult to cleanly attribute the move to any one cause even after the fact.

A fourth misconception worth flagging: PPP and interest rate parity are sometimes treated as competing theories, as if only one can be "right." They are better understood as operating on different time horizons, interest rate differentials and capital flows dominate short-term price action, while inflation differentials and PPP dominate the multi-year trend, and both can be true simultaneously without contradiction.

The takeaway

Exchange rates move because capital continuously reallocates toward the currency offering the best available return, adjusted for risk, which makes interest rate differentials the dominant force in short-term trading. Trade balances and capital flows shape the medium-term picture, while inflation differentials, captured imperfectly but usefully by purchasing power parity, set the long-run trend. Because currency markets price in expectations well ahead of actual policy decisions, rates often shift before a central bank has said or done anything official, and a single news headline rarely explains a currency move as fully as it appears to. Anyone trying to interpret why a currency moved should look for what changed in relative interest rates, trade flows, or inflation outlooks between two countries, not just what happened in that day's headlines.

---

Read next:

• Why liquidity matters in markets
• Why diversification reduces risk
• Why compound interest grows so fast

FAQ

Q: What is the biggest short-term driver of exchange rate movement?

Interest rate differentials between two countries' central banks. Capital tends to flow toward the currency offering higher returns on comparable, similarly risky assets, which increases demand for that currency and pushes its value up relative to others, a relationship economists call interest rate parity.

Q: Why does a currency sometimes move before a central bank announcement?

Because currency markets are forward-looking and price in expected policy changes ahead of time based on economic data, speeches, and historical patterns. By the time a rate decision is officially announced, much of the anticipated move may already be reflected in the exchange rate.

Q: Does inflation affect exchange rates?

Yes, primarily over the long run. Purchasing power parity predicts that a country with persistently higher inflation than its trading partners will see its currency depreciate against theirs over time, to keep the relative cost of goods roughly stable, though the relationship holds poorly over short periods.

Q: Is a stronger currency always better for a country's economy?

No. A stronger currency benefits consumers and businesses buying imports but makes exports more expensive for foreign buyers, which can hurt export-dependent industries. A weaker currency carries the opposite trade-off, and which effect dominates depends on how export- or import-driven the economy is.

Q: When did fixed exchange rates end for major currencies?

The Bretton Woods system of fixed exchange rates effectively ended on August 15, 1971, when President Richard Nixon suspended the US dollar's convertibility into gold, an event known as the Nixon Shock. Most major economies had transitioned to floating exchange rates by 1973.

Q: What is the difference between a floating and a pegged exchange rate?

A floating exchange rate is set entirely by market supply and demand, as with the US dollar, euro, or yen today. A pegged exchange rate is fixed by a government to another currency at a set rate, which the central bank actively defends by buying or selling its own currency, as Hong Kong does with its dollar peg to the US dollar.

Q: What is a currency carry trade?

A carry trade is a strategy where an investor borrows in a currency with a low interest rate and invests the proceeds in assets denominated in a currency with a higher interest rate, aiming to profit from the rate difference. It illustrates how interest rate differentials create direct financial incentives that move capital, and currency values, between countries.