The Dollar’s Sudden Strength: A Seasonal Phenomenon or More?

The latest market chatter has U.S. dollar enthusiasts abuzz, citing a 75-day rally that might be taking shape. While some claim this is merely a seasonal phenomenon, others believe it’s more – and the fact that multiple currencies are weakening against the greenback suggests there may be substance to these claims.

Seasonal patterns in currency markets have been around for years, with studies suggesting certain periods can be particularly conducive to dollar strength. For example, a study by Barchart found that December Swiss franc and New Zealand dollar futures declined 14 out of the past 15 years, while Euro FX, British Pound, and Japanese yen futures declined in all 15.

The interest-rate environment has become increasingly favorable for dollar bulls. The Federal Reserve’s hawkish stance has maintained short-term rates above those of comparable economies like Europe and Japan. This rate differential supports the dollar through carry demand and the relative appeal of dollar-denominated fixed-income assets.

Another factor driving this trend is the growing investment in artificial-intelligence infrastructure within the United States. Research by the Federal Reserve and the Bureau of Economic Analysis suggests that this capital cycle has contributed to recent U.S. growth, creating a growth gap between the U.S. and slower-moving economies.

The dollar’s status as the world’s dominant reserve currency also contributes to its strength. Despite gradual long-term loss of market share, it still accounts for approximately 57% of allocated global reserves at the end of 2025. The dollar benefits from deep Treasury markets, liquidity, relatively attractive yields, and demand for defensive assets during geopolitical or energy-market stress.

However, this narrative is not without its challenges. Some traders caution that additional ECB or BOJ tightening could narrow the rate differential advantage enjoyed by the dollar. Investors may also hedge their exposure to U.S. markets, reducing the impact of sustained capital inflows on the dollar’s underlying bid.

The technical picture remains mixed, with the U.S. Dollar Index ($DXY) trading both sides of its 200-day moving average. But patience appears to be the best course of action, given that the upcoming seasonal pattern is 75 days long – ample time for dollar strength to develop.

Some traders believe this seasonality will confirm the bullish thesis, citing the MRCI September Seasonal Report, which indicates five out of 15 trades are bullish on the U.S. Dollar, with hypothetical testing showing average profits ranging from $1,172 to $3,135. However, while seasonal patterns can provide valuable insights, they should not be the basis for trading decisions.

Ultimately, this dollar rally is a complex interplay of factors that may have profound implications for traders and investors alike.