One currency, most of the pairs
EUR/USD, GBP/USD, USD/JPY, USD/CHF, AUD/USD, USD/CAD — the majors are all dollar pairs. A piece of US data therefore moves every one of them at the same instant, in directions that depend only on which side the dollar sits. If you are long EUR/USD and short USD/JPY, you are twice short the dollar, and one bad release costs you twice.
The dollar index, and what it is not
The dollar index measures the dollar against a fixed basket of other currencies, so it is a rough temperature reading rather than a tradable law. It is weighted heavily toward the euro, which means it tells you a great deal about EUR/USD and rather less about the dollar against a currency outside the basket.
Risk-off buys dollars
When markets are frightened, money moves toward assets seen as safe, and the dollar is one of them. This is why the dollar can rise on bad news about the United States: the flight is toward dollars regardless of where the trouble started. The yen and the Swiss franc behave similarly, which is why they can all rise at once.
Correlation is a risk problem before it is an insight
Two positions that both depend on the dollar are one position with two tickets and twice the size. Before opening a second trade, check whether it is the same bet: if the dollar leg points the same way in both, the honest risk is the sum, and it should be sized as one trade rather than two.
What to do with this
Keep one sentence in your head about the dollar’s current lean, and check every new position against it. Most of the surprise losses that look like bad luck are three trades that turned out to be the same trade.
In short
| On one side of | Every major pair |
|---|---|
| Dollar index | The dollar against a fixed basket, euro-heavy |
| In a panic | Money moves toward dollars, yen and francs |
| The hidden risk | Two dollar trades are one trade, doubled |
| The habit | Check a new position against the ones you hold |
Common questions
Why did bad US news make the dollar rise?
Because frightened money moves into dollars regardless of where the fear started. Safe-haven flow can outweigh the news itself.
Should I trade the dollar index?
Most retail platforms offer something like it, but it is a basket dominated by the euro. Trading EUR/USD directly is usually the clearer version of the same idea.
How do I know if two trades are the same trade?
Write out the dollar leg of each. If the dollar points the same way in both, they are one position and should be sized as one.
Trading forex and CFDs on margin carries a high level of risk. Most retail accounts lose money. Nothing on this page is financial advice or a recommendation to trade.