Interest-Rate Differentials and Currencies: Why the Higher Rate Does Not Guarantee a Gain
A currency associated with a higher interest rate can still depreciate enough to overwhelm any income advantage.
Retail financing has its own terms
An OTC forex provider's rollover or financing adjustment may reflect rate differentials plus markups and calendar treatment. The amount credited or charged can differ from a simplified central-bank-rate calculation. Check the actual schedule, not a general explanation of carry. Weekends, holidays and product conventions can affect posting. A position may incur a cost even when a basic comparison suggests a yield advantage. The provider's statement and agreement determine the account treatment, while the exchange-rate exposure continues independently.
Exchange-rate losses can dominate income
Suppose a hypothetical annual financing benefit is 3% before other costs, while the currency exposure depreciates 8% over a comparable period. The income does not prevent a negative overall result. Exact portfolio returns require consistent valuation, compounding, financing and leverage assumptions. This simple example only shows the scale problem: an apparently attractive interest gap can be smaller than an ordinary currency move. Adding leverage magnifies account sensitivity rather than transforming the relationship into a guaranteed income strategy.
Risk conditions can change correlations
Currencies can respond to growth prospects, commodity prices, external financing needs and shifts in risk appetite. A higher-yielding currency can become vulnerable when investors reduce risky exposures or funding becomes scarce. Historical relationships are not permanent protections. Compare scenarios rather than relying on a single average correlation. A position that looks attractive in calm conditions may behave differently when liquidity deteriorates. This is another reason to keep the instrument's funding and execution arrangements separate from a broad macroeconomic narrative.
Use the differential as one research input
Record the rate definitions, maturities, expected path, financing terms, currency exposure and costs. Examine what would happen if rates moved differently from expectations or if the exchange rate shifted sharply. Verify current official information rather than repeating an old yield ranking. This framework is educational and does not recommend a carry trade or any specific pair. The higher advertised rate is a fact to investigate, not proof of a superior investment or a reason to accept leveraged losses.
Sources and further reading
Educational explainer. Numerical examples are hypothetical and are not live quotes or forecasts. Check the linked primary sources for current definitions, rules and product conditions.