Does a Rising Dollar Index Always Mean a Higher USD/KRW Exchange Rate?
Understand the Dollar Index's six-currency basket and how it differs from USD/KRW. Distinguish index levels, percentage changes, the Fed's broad dollar index, and companies' currency exposure.
The Dollar Index, DXY, measures the US dollar's relative value against a specified basket of six currencies; it is not the same indicator as USD/KRW. The Korean won is not in the basket, so the two do not always have to move in the same direction. Before interpreting dollar strength, check the comparison currencies and index composition.
The dollar's value needs a comparison currency
ICE's US Dollar Index combines the euro, yen, pound, Canadian dollar, Swedish krona, and Swiss franc using geometric weighting. It is not an average against every currency worldwide, and its constituent currencies do not have equal influence. A sharp weakening of the euro can therefore drive DXY strongly higher even if other currencies behave differently. An index level above 100 does not establish that the dollar is overvalued against all currencies. The level results from a specified base period and formula; assessing a fair exchange rate requires separate economic assumptions.
Check the won and companies' transaction currencies separately
USD/KRW is read as the amount of won needed to buy one dollar. Even on a day when DXY rises, USD/KRW can fall because of domestic or international capital flows or won-specific factors. A stronger dollar also does not automatically benefit an exporter. Revenue and cost currencies, foreign-currency borrowing, currency hedging, and overseas competitors' currencies all matter. In company analysis, use DXY as a reference for the broad environment, and calculate earnings sensitivity using actual transaction currencies and net exposure amounts.
The broad dollar index has a different purpose and composition
The Federal Reserve provides a broad dollar index covering a wider set of major trading partners' currencies, as well as indexes for advanced and emerging economies. It also distinguishes nominal indexes from real indexes adjusted for consumer prices. If DXY and the broad index move in different directions, examine what their currency composition and weights reflect rather than choosing which is wrong. For long-term competitiveness, consider whether nominal exchange rates alone are sufficient. Rather than directly comparing the original numerical levels of different indexes, rebase them to the same date or compare their percentage changes over a period.
Worked example
Hypothetical example: If DXY rises from 100 to 102, its gain is 2%. If USD/KRW falls from KRW 1,300 to KRW 1,287 over the same period, the change in the dollar's won price is -1%. There is no arithmetic contradiction because the won is not a DXY constituent. Under the simplifying assumption of USD 1 million in revenue with no costs or hedging, won-translated revenue falls from KRW 1.3 billion to KRW 1.287 billion.
What to check
- Do not treat DXY and USD/KRW as the same indicator.
- Check constituent currency movements and differences in weights.
- Do not interpret the base level of 100 as fair value.
- Calculate corporate earnings effects using actual transaction currencies and net exposure.
Sources and primary materials
This is educational material about research methods. For an actual company decision, verify the filings and primary sources for the relevant period.