If you want to understand why major currency pairs move over weeks and months, start with one concept: the interest rate differential. It is the difference between the interest rates of two countries, and it is one of the most powerful long-term drivers in the forex market. This week’s back-to-back Fed, ECB and BoJ meetings are a perfect example of it in action.
What is an interest rate differential?
Every currency pair links two economies. If US rates are higher than Japanese rates, investors can earn more by holding dollars than yen. Money tends to flow toward the higher-yielding currency, supporting it. The bigger the gap, and the longer it is expected to last, the stronger the effect.
It’s about expectations, not just today’s rates
Markets look forward. What moves currencies is usually a change in the expected path of rates. Right now, futures markets price a high probability that the Fed raises rates in December. That expectation has already helped lift the US Dollar Index above 102. If the Fed confirms it, the move may continue; if the Fed disappoints, the dollar can fall even though rates have not changed.
Applying it to today’s market
USD/JPY: The BoJ’s rate of 1.25% is far below US rates. Even with Japanese inflation supporting more BoJ hikes, the gap remains wide, which explains why USD/JPY trades near 158. For the yen to strengthen meaningfully, the gap needs to narrow, through BoJ hikes, Fed caution, or both.
EUR/USD: Both the ECB and the Fed are on hold, with possible hikes in December. Here, the differential is less decisive, so other factors, such as French fiscal risk, are driving the euro lower.
The carry trade
A carry trade means borrowing in a low-yielding currency (such as the yen) and investing in a higher-yielding one. Traders earn the interest difference, known as “swap” or “rollover” in forex. Carry trades can work well in calm markets but can unwind violently when risk sentiment turns or the low-yielding currency’s central bank surprises with a hike.
How to track rate differentials
- Compare 2-year government bond yields between two countries; they reflect expected policy rates.
- Follow central bank meeting calendars and futures-implied probabilities.
- Read the statements and press conferences, where guidance about future moves is given.
Key takeaway: Charts show you where price has been, but interest rate differentials often explain why a trend exists. Combining both gives traders a much clearer picture.
Disclaimer: This article is for informational and educational purposes only and does not constitute financial advice. Trading forex and CFDs carries a high level of risk and may not be suitable for all investors. Market levels quoted are approximate at the time of writing.