What Affects Exchange Rates? The Main Forces Behind Currency Moves

Exchange rates move because the demand for one currency changes relative to the demand for another. Behind that simple statement sit a handful of recurring forces: interest rates, inflation, economic growth, trade, investment flows, politics and the general mood of investors. None of them works alone, and markets react to expectations about these factors at least as much as to the factors themselves.

For floating currencies, these forces play out continuously. For pegged currencies, the central bank absorbs them up to a point; the difference is explained in the guide to floating and fixed exchange rates.

Supply and demand, briefly

Anyone who wants to buy goods, services, shares or bonds in another country usually needs that country's currency first. A Japanese company paying a German supplier sells yen and buys euros. A US pension fund investing in British bonds sells dollars and buys pounds. Millions of such decisions, large and small, add up to the flows that push a rate up or down.

1. Interest rates

Higher interest rates make deposits and bonds in a currency more rewarding to hold, which tends to attract money from abroad. That is why central bank decisions and speeches are watched so closely. What matters most is often the difference between two countries' rates and where that difference is expected to go. The mechanics are covered in detail in the explainer on how interest rate decisions affect exchange rates.

2. Inflation

If prices rise faster in one country than another, each unit of its currency buys less over time. Over long periods, currencies of high-inflation countries have tended to weaken against those of low-inflation countries. In the short run the link can look reversed: higher inflation may lead markets to expect rate rises, which can support the currency for a while.

3. Economic growth and data

A growing economy tends to attract investment and may prompt its central bank to raise rates, both of which can support its currency. Releases such as employment reports, GDP estimates and business surveys are therefore watched for clues. As with rates, the reaction usually depends on whether a figure beats or misses expectations; the guide to reading an economic calendar explains how those expectations are presented.

4. Trade and the current account

A country that sells more abroad than it buys receives foreign currency that must be converted back, which creates demand for its own money. A country that imports more than it exports has the opposite flow. A current account deficit does not doom a currency, but it means the country relies on investment inflows to balance its payments, and those can change quickly.

5. Capital flows and investment

Money moving into stocks, bonds, property and companies can dwarf trade flows on any given day. Large mergers, changes in how global funds allocate between countries and shifts in where companies choose to invest can all move currencies. Strategies that borrow in low-rate currencies to invest in higher-rate ones, described in the article on the carry trade, are one example of these flows.

6. Politics and public finances

Elections, changes of government, budget plans and disputes over debt affect how safe a currency looks. Investors generally prefer predictable policy. Uncertainty does not always weaken a currency, but it tends to make its moves larger and less orderly.

7. Risk appetite and safe havens

When investors feel confident, money often flows towards higher-yielding currencies. When fear takes over, it often retreats to currencies seen as safe havens, a role commonly associated with the US dollar, the Swiss franc and the Japanese yen. This mood can override local economic news for days or weeks at a time.

8. Central bank intervention

Central banks occasionally buy or sell their own currency directly to slow a move they consider excessive. Even the possibility of intervention, signalled through official comments, can influence the market.

How the forces compare

Force	Usual time frame	Typical direction (other things equal)
Higher interest rates	Days to months	Supports the currency
Persistently higher inflation	Years	Weakens the currency
Stronger growth	Months	Supports the currency
Large current account deficit	Months to years	Can weigh on the currency
Political uncertainty	Days to months	Usually weighs, adds volatility
Global risk aversion	Hours to weeks	Favours safe havens

"Other things equal" is doing a lot of work in that table. In practice several forces act at once and can pull in opposite directions.

Why rates are hard to predict

By the time a piece of news is public, the market has usually already priced in what most participants expected. Prices then move on surprises and on changing expectations, which are by nature hard to foresee. This is why confident forecasts of where a currency will be in six months deserve scepticism.

Questions readers ask

Who actually sets the exchange rate?

For floating currencies, nobody sets it: it emerges from trading between banks, companies, funds and individuals. Rates shown by banks and card providers are based on this market price, plus their own margin.

Does a strong currency mean a strong economy?

Not necessarily. A currency can be strong because of high interest rates or safe-haven demand during a crisis, and a weaker currency can help exporters.

This explainer is for general understanding and is not investment or currency advice. For decisions about money held or owed in another currency, speak to a qualified, independent adviser.