The dollar smile theory explains why the US dollar can strengthen in both very good and very bad economic conditions, while weakening during middling periods. It is one of the most useful frameworks for understanding currency dynamics and their impact on crypto.
The theory, originally proposed by Stephen Jen, describes a U-shaped or smile-shaped relationship between the dollar and economic conditions. On the left side of the smile, during severe economic stress or crisis, the dollar strengthens as a safe haven. Capital flows into US Treasuries and dollar-denominated assets as investors flee risk. On the right side, during strong US economic outperformance, the dollar strengthens because higher growth and interest rates attract capital to US assets.
The bottom of the smile is where the dollar weakens. During periods of moderate growth where the US is not in crisis but also not dramatically outperforming other economies, the dollar tends to weaken as capital flows to higher-yielding or faster-growing markets abroad.
For crypto, the dollar smile has clear implications. A weakening dollar (the bottom of the smile) tends to be the most favorable environment for crypto. It signals adequate liquidity, moderate growth, and a risk appetite that supports speculative assets. Many of the best crypto bull runs have coincided with periods of dollar weakness.
The left side of the smile (crisis-driven dollar strength) is generally terrible for crypto. The flight to safety that drives dollar strength simultaneously drives capital out of risk assets including crypto. The COVID crash, the 2022 rate shock, and the banking crisis of 2023 all featured dollar strength that coincided with crypto weakness.
The right side of the smile (growth-driven dollar strength) is more ambiguous for crypto. If the dollar is strong because the US economy is booming, risk appetite might still be sufficient to support crypto prices. But the higher interest rates that accompany strong growth create opportunity cost headwinds for non-yielding assets.
The DXY (Dollar Index) is the standard measure for dollar strength, tracking the dollar against a basket of major currencies weighted heavily toward the euro. Monitoring DXY trends provides a useful overlay for crypto market analysis.
From a practical standpoint, crypto positions tend to perform best when the DXY is in a downtrend, and face the most headwinds when DXY is in a strong uptrend regardless of whether that strength comes from the left or right side of the smile.