What DXY actually measures
The DXY (US Dollar Index) is a geometric mean of six bilateral exchange rates, with weights set in 1973 that haven't been updated since. The euro alone accounts for 57.6% of the index, followed by yen (13.6%), pound (11.9%), Canadian dollar (9.1%), Swedish krona (4.2%), and Swiss franc (3.6%). This means DXY moves are functionally dominated by EUR/USD — when EUR/USD falls 1%, DXY rises about 0.6%. The index is not a true trade-weighted dollar measure; it's a stale basket that happens to be liquid in futures.
Why everything else cares
Three big asset categories are mechanically affected by the dollar's strength.
- →Commodities: Oil, gold, copper, agricultural goods are priced in dollars. A stronger dollar makes them more expensive in every other currency, suppressing demand → lower prices.
- →Emerging markets: EM corporates and governments often issue debt in dollars but earn revenue in local currency. A stronger dollar increases their effective debt burden, tightens local financial conditions, and pressures EM equities and FX.
- →Crypto: Trades on global liquidity. A strong dollar drains liquidity from risk assets globally; BTC and ETH historically inversely correlate with DXY over multi-month windows.
Reading the DXY chart in context
The 100 level is a psychological reference point — the DXY rebased from a starting value of 100 in 1973. Sustained moves above 105 usually coincide with US monetary tightening cycles and global liquidity tightening. Sustained moves below 95 align with US easing and global risk-on. The most actionable signals are at the extremes: when DXY breaks 105 to the upside with momentum, EM and crypto are typically in serious trouble. When it breaks below 95, commodity rallies and EM outperformance tend to follow.
Rate differential as the engine
DXY moves are fundamentally a bet on the rate path of the US vs the rest of the world, especially the ECB and BoJ. If the Fed is hiking while the ECB is on hold, the rate differential widens in the dollar's favour, capital flows toward USD-denominated yield, and DXY rises. Watch 2-year yields in the US vs Germany (the bund) as the proxy for this differential. A widening US-Germany 2-year spread typically precedes a DXY rally; a narrowing spread precedes a DXY decline.
When the playbook breaks
The dollar can move against the rate differential when something more important is happening: safe-haven flows (Russia/Ukraine, COVID), debt-ceiling drama (dollar weakens despite hawkish Fed), or coordinated intervention (G7 dollar-selling agreements). These breaks are rare and usually short-lived, but they're the moments where macro discretionary funds make or lose years of returns. The framework: rate differentials dominate 80% of the time; flow/political drivers dominate the other 20%.