Recently, when reading investment news, I keep hearing phrases like "the US dollar index has risen again" or "the dollar is strengthening," but to be honest, many people don't really understand what this is referring to. I was the same until I delved deeper and discovered that the US dollar index is truly a crucial indicator; its influence extends far beyond what I initially thought.

Simply put, the US dollar index is like a thermometer for the global financial markets. It tracks the exchange rate changes of the US dollar against six major international currencies—Euro, Japanese Yen, British Pound, Canadian Dollar, Swedish Krona, and Swiss Franc. Among these, the Euro has the largest weight, over 57%, so its movement significantly impacts the overall dollar index.

Why should we pay attention to the US dollar index? Because the dollar is the most commonly used trading currency worldwide—whether it's crude oil, gold, commodities, or global investments, most are priced in USD. When the dollar index fluctuates, it triggers a chain reaction that directly affects your investment portfolio.

When the dollar index rises, it indicates the dollar has strengthened, and other major currencies are relatively depreciating. This benefits the US—imported goods become cheaper, and capital flows into the US market. But for export-oriented economies like Taiwan, it makes goods more expensive and harder to sell, potentially impacting corporate revenues. Conversely, when the dollar index falls, the dollar weakens, and capital may flow into Asian stock markets and emerging markets, giving Taiwan stocks a chance to attract hot money.

I've noticed a clear negative correlation between the dollar index and gold. When the dollar appreciates, the cost of buying gold with USD increases, naturally reducing gold demand; when the dollar depreciates, gold tends to rise. This relationship becomes especially evident during times of increased global economic uncertainty, as investors choose between the dollar and gold.

The relationship between the dollar index and US stocks is more complex; it's not simply positive or negative. Sometimes, a rising dollar attracts capital inflows into the US, boosting stocks; but if the dollar becomes too strong, it can hurt US export companies and drag down the overall stock market. During the global stock market crash in March 2020, the dollar index actually surged to 103 because everyone was seeking safe assets. Later, with the US pandemic outbreak and the Fed's massive money printing, the dollar quickly weakened, and the index dropped to 93.78. So, you can't just look at a single line; you need to consider the market background and current economic policies.

The most direct factor influencing the dollar index is the Federal Reserve's interest rate policy. Raising interest rates attracts global capital into the US, pushing the dollar index higher; lowering rates may cause capital to flow out, leading to a decline in the index. Every Fed meeting makes the market tense for this reason. US economic data are also critical—employment figures, CPI inflation, GDP growth—good data strengthen the dollar, and vice versa.

Geopolitical and international events also impact the dollar index. Wars, political turmoil, regional conflicts tend to increase global risk aversion, with the dollar often serving as the first choice for safe-haven assets. It may sound contradictory, but "the more chaotic, the stronger the dollar"—this holds true because of its safe-haven role.

Another interesting point—the dollar index is a relative measure. When currencies like the Euro, Yen, or Pound weaken due to their own economic issues, even if the dollar itself doesn't move, the dollar index can still rise. Simply put, when others' currencies depreciate, the dollar index appears stronger.

On that note, I want to mention the "Trade-Weighted US Dollar Index," which the Fed more frequently references. This indicator includes over 20 currencies, especially more from Asian emerging markets, like the Chinese Yuan, Korean Won, and Taiwanese Dollar. Compared to the traditional dollar index, which only uses six currencies and is heavily influenced by Europe, the trade-weighted index offers a more comprehensive view, especially from an Asian perspective. If you're a general investor, watching the dollar index is enough; but if you're involved in forex trading or studying Fed policies, the trade-weighted index is more accurate.

Grasping the changes in the dollar index is really important for investment decisions. It directly influences the trends of gold, crude oil, stocks, and other assets. Especially in forex trading, it’s a very practical indicator. If you're interested in forex trading, platforms like Gate allow you to directly trade the dollar index and various currency pairs, helping you stay updated on global capital flows.