Direct answer
Interest rates influence forex exchange rates mainly by changing expected returns on holding assets denominated in different currencies and by affecting expectations about inflation and central bank policy. Because currency markets price these expectations in advance, the impact of an interest-rate change depends on what investors expected beforehand.
Explanation: the main mechanisms
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Relative interest rates and expected returns Forex reflects the value of one currency versus another. If one country offers higher interest rates than another, investors may expect better compensation for holding that currency’s assets. In simplified terms, forex traders compare potential yields across currencies and adjust demand for currencies when expectations change.
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Inflation and real interest rates Interest rates connect to inflation expectations. A nominal rate that rises due to higher expected inflation may not be as supportive for a currency if the “real” return (after inflation) does not improve. So forex reactions often depend on whether rate increases are seen as improving real returns.
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Central bank credibility and policy path Markets watch not only the current rate but the expected future path. Communication from a central bank can change beliefs about whether rates will be kept higher longer or cut sooner, which changes expected currency returns.
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Risk sentiment and capital flows Even when relative yields differ, risk sentiment can dominate. In periods of uncertainty, investors may shift toward “safer” assets or reduce exposure, affecting exchange rates independently of interest-rate levels.
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What is already priced in If the market already expects a rate hike, the release may have little effect—or even the opposite effect—because traders reprice based on the difference between the announcement and expectations.
Example and independent checks
- Suppose Country A raises rates more than expected. If investors conclude this will improve future relative returns more than anticipated, demand for Country A’s currency may increase, and the exchange rate may move accordingly.
- Suppose the hike is fully expected. The immediate forex reaction may be muted because the market priced it earlier; any reaction would more likely reflect changes to the expected future policy path.
How to verify the mechanism without assumptions about “today”:
- Compare the direction of FX moves around major policy announcements with the direction of changes in expected rate paths (how markets revised expectations).
- Check whether the change was “surprising” versus already expected; larger surprises tend to coincide with bigger repricing.
- Note concurrent changes in growth or risk sentiment, since these can offset rate-driven effects.
Limitations and risks of misunderstanding
- Causality is not guaranteed: Exchange rates can move for multiple reasons at once, so the interest-rate channel may not be the only driver.
- Expectations matter: A reported rate change can have different outcomes depending on what was already priced in.
- Real vs nominal is crucial: Inflation expectations can reduce or reverse the apparent benefit of nominal rate changes.
- No future result can be inferred: Even if you understand the mechanism, you cannot reliably predict the exact direction or magnitude of a forex move from interest rates alone.