Educational content. This article explains the mechanisms behind the historical tendency of the US dollar to strengthen during equity market declines, and the conditions under which that tendency has failed. It does not constitute investment advice, a recommendation, or an offer to buy or sell any financial instrument. CFD trading carries significant risk of loss and may not be suitable for all investors. Past patterns do not guarantee future results.
The US dollar usually rises when stock markets fall because the world's debts, its safe asset and its hedges are all denominated in dollars. When risk appetite drops, borrowers need dollars to service obligations, allocators move into the asset that pays them in dollars, and hedging desks buy dollars to rebalance. Three separate flows point the same way at the same time.
That explains the tendency. It does not make it a rule, and the most instructive recent episode is one where it failed completely.
For the index that measures the dollar against a basket of currencies, see the US Dollar Index explained. For the asset on the other side of most dollar moves, see why gold rises when DXY falls.
Does the Dollar Actually Rise When Stocks Fall?
The dollar has strengthened in most large equity drawdowns of the past two decades, but the relationship is a tendency rather than a constant, and it has broken in identifiable conditions.
The historical record is easy to state. Between July and November 2008, as the global financial crisis moved through its most acute phase, the dollar index rose from around 71 to around 88. In March 2020 it rose from around 95 on 9 March to around 103 on 20 March, an eight point move in nine sessions, while the S&P 500 fell roughly 34 percent from its 19 February high to its 23 March low. In each case the dollar rose most when equity markets fell fastest.
The exceptions are not rare enough to ignore. The clearest of them, April 2025, is covered in full below, and it matters more than its frequency suggests because of what it says about the mechanism.
Correlations between the dollar and equities are also unstable at shorter horizons. The relationship described here is visible in sharp, broad risk-off episodes, not in ordinary weeks, and a two percent equity decline on an average Tuesday carries no reliable dollar implication at all.
The Dollar Smile: Two Different Reasons for the Same Move
The dollar smile is the observation that the dollar tends to strengthen at both ends of the global growth spectrum and to weaken in the middle, so the same currency appreciates for two entirely different reasons.
On the left of the curve, global growth deteriorates sharply and capital moves toward safety. Dollar strength here is defensive: it reflects demand for the asset that is expected to hold value and remain liquid when other assets do not.
On the right, US growth clearly outperforms the rest of the world. Dollar strength here is acquisitive: capital moves into US assets to capture the growth and the higher returns that come with it, and rising US rates make holding dollars more attractive on a hedged basis.
In the middle, growth is solid and broadly synchronised across regions. Capital spreads out, higher returns are available elsewhere, and the dollar tends to soften.
The framework is descriptive rather than predictive, and it does not say where on the curve the world currently sits. Its usefulness is that it separates two dollar rallies that look identical on a chart and mean opposite things about the state of the world. How FOMC meetings affect the US dollar covers the policy channel that dominates the right-hand side.
The Mechanism: Four Channels That Point the Same Way
Risk-off dollar strength is not one flow. It is four, and they arrive together.
Channel 1: The World Borrows in Dollars and Must Repay in Dollars
A large stock of debt outside the United States is denominated in dollars, and the borrowers of that debt earn revenue in other currencies.
When funding conditions tighten, those borrowers face dollar obligations they cannot postpone. Rolling the debt becomes harder and more expensive exactly when their local-currency earnings are falling, so they buy dollars in the market to cover the gap. The Bank for International Settlements has documented this pattern repeatedly: dollar credit to non-bank borrowers outside the United States runs into the trillions, and it is the mechanical reason a global risk shock becomes a dollar demand shock.
This channel is the most important one and the least intuitive, because it has nothing to do with anybody's opinion of the dollar. It is the arithmetic of a balance sheet with dollar liabilities and non-dollar assets.
Channel 2: The Safe Asset Is a Dollar Asset
The instrument that global investors buy in a flight to quality is the US Treasury security, and buying it requires dollars.
Treasuries are the deepest and most liquid government bond market in the world, and the pool of buyers who can move size into them at short notice is larger than for any alternative. A reallocation out of equities and into government bonds therefore tends to be a reallocation into dollars, whatever currency the seller started in. The demand for the currency is a by-product of the demand for the asset.
This is also why the dollar and Treasury yields can move in opposite directions during a crisis while both reflect the same flow: yields fall because the bonds are being bought, and the dollar rises because they are being bought with dollars. Why stocks fall when bond yields rise covers the yield side of the same relationship in normal conditions.
Channel 3: Hedges Rebalance in the Same Direction
Institutional investors who hold US equities and hedge the currency exposure adjust those hedges as the value of the underlying holding changes.
An investor outside the United States holding US shares typically sells dollars forward to hedge the currency component. When the equity holding falls in value, the hedge is now too large for the position, and correcting it means buying dollars back. The larger the equity decline, the larger the rebalancing flow, and it arrives in the same direction across every hedged holder at once.
This channel is purely mechanical. Nobody involved is expressing a view on the dollar; they are keeping a hedge ratio at target.
Channel 4: The Dollar Funds Leveraged Positions That Get Closed
Leveraged positions across markets are frequently funded in dollars, and closing a leveraged position means buying back the funding currency.
The 2024 example ran through the yen rather than the dollar, and it shows the mechanism cleanly: when the Bank of Japan raised its policy rate on 31 July 2024, positions funded in yen were closed en masse and the yen appreciated sharply as they were unwound. The same dynamic applies to dollar-funded positions in a dollar-funded unwind. Carry trade explained covers the structure of these positions and why they unwind faster than they are built.
Case Study: March 2020
March 2020 is the clearest single observation of all four channels operating at once.
The equity decline was fast and global, with the S&P 500 falling roughly 34 percent between 19 February and 23 March. Simultaneously, dollar funding markets seized: borrowers with dollar liabilities could not roll them, cross-currency basis spreads widened sharply against non-dollar borrowers, and even Treasuries were sold for a period as institutions raised cash in the one currency that settles everything.
The dollar index rose from around 95 on 9 March to around 103 on 20 March. The move ended when the Federal Reserve expanded its swap lines with other central banks, supplying dollars directly to the institutions that could not obtain them in the market. The dollar weakened almost immediately afterward.
That sequence is the strongest available evidence for the funding interpretation. The rally stopped when the dollar shortage was addressed, not when equities stopped falling.
When the Relationship Breaks: April 2025
The relationship fails when the shock originates in the United States itself, because the same asset cannot simultaneously be the source of the risk and the refuge from it.
April 2025 is the clearest example. Following the 2 April tariff announcement, more than USD 5 trillion was erased from the value of the S&P 500 in the three days that followed. The dollar did not rise. The European Central Bank's Financial Stability Review records that equity prices declined sharply at the same time as a broad-based depreciation of the US dollar, and describes this as an unusual occurrence for a safe-haven currency. The dollar index fell more than 4 percent to a three-year low, and volatility in the Treasury market rose as investors questioned the safe-haven properties of both the currency and the bonds.
Two other conditions produce the same break.
A Federal Reserve easing shock. When the response to the risk event is an expected sequence of US rate cuts, the rate channel pushes the dollar down while the safety channel pushes it up, and the net direction depends on which dominates.
An idiosyncratic US problem. A debt ceiling impasse, a downgrade of US sovereign credit, or a question about institutional stability makes dollar assets the object of concern rather than the destination of the flight.
The common feature of all three is that the dollar's safe-haven role is a property of how the rest of the world uses it, not an intrinsic property of the currency. When the usage is what is being questioned, the property does not hold.
What This Means Across a Multi-Currency Book
A dollar move reaches a mixed CFD book in more places than the dollar pairs, because most instruments do not settle in dollars.
| Settlement currency | Instruments at Vanto |
|---|---|
| USD | 28 of 78, including all 13 cryptocurrencies, both metals, all 3 energies and 6 indices |
| EUR, JPY, GBP, CHF, HKD, SGD, AUD | 9 of the 18 indices |
| 14 currencies in total outside USD | The remaining 50 instruments |
Source: Vanto calculator data, snapshot 6 September 2026.
Profit and loss on an instrument is realised in that instrument's settlement currency and then converted to the account currency. A position on DE40 produces a result in euro, a position on JP225 produces a result in yen, and a position on UK100 produces a result in sterling. For an account denominated in dollars, the amount that lands is the instrument result converted at the prevailing rate, so a dollar move changes the account-currency outcome of positions that have no dollar in their symbol at all.
The effect compounds in a risk-off episode rather than cancelling out. A European index falling while the dollar strengthens produces a euro-denominated loss converted at a rate that is moving against the euro at the same time. This is a second-order effect next to the price move itself, and it is not a reason to avoid non-dollar instruments, but it is the reason a multi-currency book behaves differently from a single-currency one in exactly the conditions this article describes. The trading calculator shows the settlement currency for every instrument alongside notional and margin.
Reading the Relationship Without Turning It Into a Signal
The tendency described here is a structural explanation, not a trading rule, and the distinction matters more than usual for this particular relationship.
Correlations between the dollar and equities are unstable, they differ by horizon, and they invert under the conditions listed above. Any position taken on the basis of an expected correlation carries the risk that the correlation is in the middle of one of those inversions, and April 2025 shows that inversions can last for months rather than days. The value of the framework is in understanding why a position behaves the way it does, not in predicting the next move. How to trade EUR/USD and how to trade USD/CHF cover the instruments most directly exposed to it, and what is margin in trading covers the account mechanics that a correlated set of positions affects simultaneously.
Frequently Asked Questions
Why does the US dollar go up when the stock market crashes?
Because a rise in risk aversion produces dollar demand from three directions at once: borrowers outside the United States need dollars to service dollar-denominated debt, investors moving into US Treasuries need dollars to buy them, and hedged holders of US equities buy dollars back as their hedges become oversized relative to shrinking positions.
What is the dollar smile theory?
It is the observation that the dollar tends to strengthen both when global growth deteriorates sharply, through a flight to safety, and when US growth clearly outperforms the rest of the world, while weakening in the synchronised global expansion between those two states. The curve is descriptive of past behaviour rather than predictive.
Does the dollar always rise when stocks fall?
No. It fell alongside equities after the 2 April 2025 tariff announcement, an episode the ECB's Financial Stability Review describes as unusual for a safe-haven currency, with the dollar index down more than 4 percent to a three-year low. The relationship generally fails when the shock originates in US policy itself.
Why did the dollar fall in April 2025 when stocks fell?
Because the shock came from US trade policy, so US assets were the object of the concern rather than the refuge from it. Investors questioned the safe-haven properties of both the dollar and Treasuries at the same time, and capital moved toward other currencies and gold instead.
How does a dollar move affect positions that are not in dollar pairs?
Profit and loss is realised in each instrument's settlement currency and converted to the account currency, so a dollar move changes the converted result. At Vanto 28 of 78 instruments settle in dollars and the other 50 settle in 14 other currencies, including nine of the eighteen indices.
Is the dollar still a safe-haven currency?
Its safe-haven behaviour comes from the world's use of the dollar for borrowing, reserves and settlement rather than from any intrinsic property, and that usage remains dominant. What 2025 demonstrated is that the behaviour is conditional on the shock coming from outside the United States, which is a limit on the pattern rather than a verdict on the currency.
Follow Dollar Exposure Across Your Whole Book
The dollar reaches a CFD account through the pairs that name it and through the settlement currency of everything else, which is why it is worth understanding as a structural feature rather than as one instrument among many. For the basket that measures it, see the US Dollar Index explained. For its clearest counterpart, see why gold rises when DXY falls. For the policy meetings that move it most, see how FOMC meetings affect the US dollar and how CPI affects the US dollar. For the financing side of holding any currency position, see why exotic currency pairs cost more to hold overnight. Live prices, spreads and settlement currencies for all 78 instruments are in the trading calculator, and a demo account lets you watch a risk-off session across a mixed book without risking capital.
Risk warning. Trading securities, futures, options, and contracts for differences are complex financial instruments that require knowledge and understanding. Prices can fluctuate significantly and securities may become valueless. Investors may incur losses exceeding the potential for profits. Trading on margin can result in losses greater than the amount initially deposited. Past performance is not necessarily a guide to future performance. The information in this article is for educational purposes only and does not constitute investment advice, a recommendation, or an offer to buy or sell any financial instrument. Consider whether CFD trading is appropriate for your circumstances and seek independent advice if necessary.