How Interest Rates Move Currencies: Central Banks 101

The basic engine: money flows to yield

A currency is, in part, a claim on the interest you can earn holding it. Raise a country's interest rates and its currency becomes more attractive to hold — higher returns on deposits and government bonds pull in foreign capital, and that demand tends to strengthen the currency. Cut rates and the reverse happens. That's the gravity. It's also where most explanations stop, and where they become misleading.

Why the level isn't what moves price

Markets are forward-looking. Today's interest rate is public knowledge already baked into the price. What moves a currency is new information that changes the expected path of rates — a shift in what traders believe the central bank will do over the coming months.

This is the single most important idea in fundamental FX, and it explains things that otherwise look insane:

• A central bank hikes rates — and the currency falls, because the market had already expected the hike and more, and the accompanying guidance was softer than hoped.
• A central bank holds rates steady — and the currency jumps, because officials hinted at hikes sooner than the market was positioned for.

The decision is not the event. The surprise relative to expectations is the event.

Hawkish vs dovish

Hawkish

Leaning toward tighter policy — higher rates, fighting inflation. Generally currency-positive. A "hawkish hold" (no change, but a tighter tone) can lift a currency without any rate move at all.

Dovish

Leaning toward easier policy — lower rates, supporting growth. Generally currency-negative. A "dovish hike" (a raise paired with soft guidance) can sink a currency despite the higher rate.

Notice that hawkish and dovish describe the tone and guidance, not just the action. The press conference and statement often move the market more than the rate decision they accompany, because that's where the future path is signalled.

The dot plot and forward guidance

Central banks telegraph the path on purpose. The Federal Reserve's "dot plot" publishes where each official expects rates to be in coming years; markets trade the projected trajectory, not just the next meeting. Alongside it, forward guidance — the deliberate signalling of intent — lets a central bank move markets with words before it moves them with rates. Reading the bias means reading the communication, not waiting for the decision.

Carry: getting paid to hold the differential

The rate gap between two currencies has a direct cost or credit. Hold a higher-yielding currency against a lower-yielding one and you earn the rate differential (the overnight swap); hold it the other way and you pay. The carry trade — long the high-yielder, short the low-yielder — collects that differential, and in calm, risk-on markets it can run for a long time. The danger is the unwind: when risk sentiment turns, carry trades reverse violently and all at once, which ties interest rates directly to risk regime and volatility.