What Moves Currency Prices?

Interest rates — the most powerful driver of currency flows

Interest rate differentials are the single most important driver of medium-term currency movements. When a country raises rates, its bonds, savings accounts, and money market instruments pay more. Global capital — pension funds, sovereign wealth funds, banks — flows toward higher yields. To access those yields, they must sell their home currency and buy the higher-rate currency, creating demand that pushes the exchange rate up.

The 2022 Federal Reserve hiking cycle is the defining case study of this generation. When the Fed began raising rates in March 2022 (from 0.25%), the European Central Bank was still at 0% and was months away from its first hike. The growing US-Eurozone rate differential made dollar assets dramatically more attractive than euro assets. By September 2022, with the Fed at 3.00% and the ECB still below 1%, EUR/USD had fallen from 1.10 to 0.9553 — breaking parity for the first time since 2002, a level considered structurally impossible by many analysts just months earlier.

Inflation and Purchasing Power Parity — the long-run anchor

High inflation weakens a currency over the long run because each unit buys fewer goods and services. Purchasing Power Parity (PPP) theory formalises this: in the long run, exchange rates should adjust until the same basket of goods costs the same amount in any country, when measured in a common currency. If Country A has 2% inflation and Country B has 8% inflation, PPP predicts Country B's currency will depreciate by approximately 6% per year — eroding the purchasing power differential.

The empirical record is clear: over 10–20 year horizons, exchange rate movements correlate closely with inflation differentials. Turkey's lira is the extreme example — with inflation exceeding 80% in 2022 and cumulative inflation of several thousand percent since 2005, the lira lost over 90% of its value against the dollar in that period. But PPP is not a short-run trading tool. In the short run, interest rate dynamics and capital flows dominate — currencies can deviate from PPP fair value for years. The Economist's Big Mac Index is a simplified proxy for PPP, showing how currencies compare to purchasing power. As of 2023, the Swiss franc was one of the most overvalued currencies vs. the dollar by PPP (Swiss Big Mac cost the equivalent of $7.73 vs $5.58 in the US), while most emerging market currencies were undervalued.

The complication: rate hikes and inflation can push in opposite directions

A subtlety that trips up beginners: when a country has high inflation, its central bank typically raises rates to combat it. The rate hike effect (positive for the currency — attracts capital) and the inflation effect (negative — erodes value) work in opposite directions. In the short run, the rate hike usually dominates. In 2022, the US had 9.1% CPI — the highest in 40 years — yet the dollar surged to a 20-year high because the Fed was hiking faster than any other central bank. The currency strengthened even as purchasing power eroded, because interest rates move faster than PPP equilibrium.

GDP growth — attracting investment capital

Strong economic growth attracts foreign investment. When Country A grows at 3% and Country B at 0.5%, multinationals expand in Country A, private equity buys its businesses, and foreign investors allocate to its stock market. All of these transactions require converting foreign currencies into Country A's currency — creating demand that appreciates it. Key data releases that forex traders watch for GDP signals: GDP quarterly prints (but these are backward-looking), PMI indices (the monthly Purchasing Managers Index is a leading indicator — above 50 = expansion, below 50 = contraction), retail sales figures, and employment data (non-farm payrolls in the US are the most market-moving single data release in forex).

The relationship is not mechanical. Quality of growth matters enormously. Growth driven by fiscal spending and debt accumulation can actually weaken a currency by raising inflation and fiscal deficit concerns faster than growth-related inflows arrive. This is why countries with high debt-to-GDP ratios sometimes see their currencies under persistent pressure even during periods of solid nominal GDP growth. The 2020–2021 period saw the US grow rapidly post-COVID via massive fiscal stimulus, yet the dollar initially weakened because markets feared the inflationary consequences of that stimulus — before the inflation realised and forced the Fed to hike.

Trade balance — the slow but structural force

A trade surplus (exports > imports) means foreign buyers must continuously convert their currency into the exporting country's currency to pay for goods. A German manufacturer selling cars to the US receives dollars, then converts them to euros to pay employees and suppliers. This creates persistent, structural demand for euros. A trade deficit creates the opposite pressure — importing more than you export means you must continuously sell your currency to buy foreign goods.

Japan is the classic example of trade surplus and structural currency support. For decades, Japan ran large surpluses as the world bought Toyota, Sony, and Panasonic products. This created persistent yen demand that kept USD/JPY anchored. Germany's chronic eurozone surplus exerts similar upward pressure on the euro. The US has run persistent trade deficits since the 1980s — a structural negative for the dollar that has been offset by the dollar's role as the global reserve currency (foreigners must hold dollars to buy oil, commodities, and to transact globally). The current account — a broader measure that includes investment income and transfers in addition to trade — is the version most watched by economists and the IMF for currency sustainability assessments.

Political risk — the wildcard that overrides fundamentals

Political events can override all economic fundamentals in the short term. Elections, referenda, government collapses, unexpected policy changes, wars, and sanctions all create uncertainty — and currency markets price uncertainty immediately. Political risk manifests as rapid, sharp moves that bypass normal macro logic entirely.

Risk sentiment — safe havens and carry trade mechanics

Currency markets operate in two broad moods: risk-on (investors seeking returns) and risk-off (investors seeking safety). In risk-on environments, capital flows into high-yield currencies — Australian dollar (AUD), New Zealand dollar (NZD), and emerging market currencies — as investors chase the interest differential. In risk-off events, capital rapidly exits these positions and floods into safe-haven currencies: the Japanese yen (JPY), Swiss franc (CHF), and to a lesser extent the US dollar (USD).

The carry trade is the structural mechanism behind risk sentiment currency moves. A carry trader borrows in a low-yield currency (JPY at 0%) and invests in a high-yield currency (AUD at 4.5%), pocketing the 4.5% interest differential. This trade is enormously popular in calm markets — trillions of dollars of carry positions exist at any given time. When risk sentiment sours, all carry traders close simultaneously: they sell AUD and buy back JPY to repay their loan. This creates a self-reinforcing cascade: JPY surges (as everyone buys it back), AUD collapses (as everyone sells it), which triggers stop-losses on remaining carry positions, forcing more closes, and so on. In October 2008, AUD/JPY fell 35% in six weeks as global carry trades unwound simultaneously.