Direct answer
Interest rates matter in forex because currencies are influenced by the relative economic attractiveness of holding them. In practice, traders monitor how expectations about interest rates change, since those expectations can shift capital flows, risk sentiment, and the valuation of exchange rates.
Explanation: the mechanics in plain terms
A key idea is relative returns. If one currency’s interest rate outlook is higher (relative to another), holding assets denominated in that currency may be seen as offering better yield, all else equal. This can lead to demand for that currency.
Forex prices are also forward-looking. What matters is not only the latest announced rate, but what market participants expect will happen next. Central bank communication, inflation trends, and growth expectations can all change the path investors believe rates will take. When expectations move, exchange rates can move even if the current policy rate does not change.
Finally, interest rates interact with risk. Higher rates may reflect tighter policy aimed at controlling inflation, which can influence perceived macro stability. But higher rates can also coincide with growth uncertainty or tighter financial conditions. Because forex is driven by multiple factors at once, interest-rate effects are usually indirect.
Example or checks you can apply
Consider two currencies, A and B. If the expected future rate path for A rises relative to B, traders may re-price the relative attractiveness of A-denominated assets. You can independently verify the direction of expectations by comparing how market-implied views change around policy statements and major inflation or growth data releases. Then check whether the observed currency moves align with those expectation changes, noting that alignment is not guaranteed.
Limitations and risks
Interest-rate relationships are probabilistic, not deterministic. Other fundamentals—such as inflation differentials, fiscal concerns, external balances, and geopolitical risk—can dominate or offset interest-rate effects. Also, because forex reacts to changing expectations, data “surprises” can matter more than the headline numbers.
A practical limitation is verification: you should distinguish between the policy rate level and the market’s expected future path. If you only track the current rate, you may miss the main driver. As with any concept involving markets, outcomes can differ from textbook logic.