The Dollar Index (DXY): Why Half of It Is Really EURUSD
DXY measures the dollar against 6 currencies with weights fixed since 1973, and the euro takes 57.6%. The real formula, a worked example, and how to read USD-wide moves.
- DXY is a weighted geometric average of the dollar against 6 currencies, set to 100 in March 1973
- The euro weighs 57.6% and the European currencies together 77.3%, so DXY mostly mirrors EURUSD
- A 1% move in EURUSD moves DXY by about 0.57%, while a 1% move in USDJPY moves it by only about 0.14%
- Pair DXY with a simple average of the dollar's moves against several currencies to tell a dollar story from a single-currency story
The US Dollar Index (DXY) is a single number that tells you whether the US dollar is stronger or weaker against six currencies. Traders use it to see where “the dollar as a whole” is heading. What many don’t realise is that its weights were set in 1973 and the euro takes more than half of them, so DXY tells you more about the euro than you might think. This article opens up the real formula, works through it step by step, and shows how to use it without being fooled by it.
Where DXY comes from
In 1973, after the fixed exchange rate system (Bretton Woods) ended and the major currencies began to float, the US Federal Reserve created this index to measure the dollar against key trading partners. It was set to 100 in March 1973. Today ICE administers and calculates it.
The basket originally held 10 currencies. When the euro arrived in 1999, it replaced five of them: the German mark, French franc, Italian lira, Dutch guilder and Belgian franc. That left the six you see today, and the weights have not changed since.
Six currencies, fixed weights
| Currency | Pair used | Weight |
|---|---|---|
| Euro (EUR) | EURUSD | 57.6% |
| Yen (JPY) | USDJPY | 13.6% |
| Pound (GBP) | GBPUSD | 11.9% |
| Canadian dollar (CAD) | USDCAD | 9.1% |
| Swedish krona (SEK) | USDSEK | 4.2% |
| Swiss franc (CHF) | USDCHF | 3.6% |
They add up to exactly 100%. Notice there is no Chinese yuan and no Mexican peso, even though both countries are major US trading partners today, while the Swedish krona is in. The weights reflect world trade in the 1970s, not today.
The real formula: a geometric average
DXY doesn’t add prices up and divide. It raises each pair to the power of its weight and multiplies them together (a weighted geometric average).
DXY = 50.14348112 × EURUSD^(−0.576) × USDJPY^(0.136) × GBPUSD^(−0.119)
× USDCAD^(0.091) × USDSEK^(0.042) × USDCHF^(0.036)Three things to read from it:
- Negative exponents go on the pairs where the dollar is the second currency (EURUSD, GBPUSD), because those pairs rise when the dollar weakens. The pairs with the dollar first (USDJPY, USDCAD, USDSEK, USDCHF) get positive exponents. So every term points the same way: dollar stronger, index up
- 50.14348112 is the constant that makes the index exactly 100 at March 1973 exchange rates. It has no other meaning
- The effects of each pair add up. Because the formula multiplies, the index’s percentage change is roughly the weight times the dollar’s percentage move against that currency, summed over all six
% change in DXY ≈ sum of (weight × % the dollar moved against that currency)
A quick example: if EURUSD rises 1% with everything else flat, the index changes by 1.01^(−0.576) = 0.994285, a fall of 0.57%. If USDJPY rises 1% on its own, the index rises only 0.14%. The same size move has roughly four times the effect.
Worked example: the dollar strengthens almost everywhere, yet DXY falls
These are made-up prices, not real market quotes. Start with EURUSD 1.1000, USDJPY 150.00, GBPUSD 1.3000, USDCAD 1.3700, USDSEK 10.000 and USDCHF 0.8800. Plugging them into the formula gives DXY = 102.61.
One day, European news lifts the euro while the dollar strengthens against everything else.
| Pair | Move | Dollar vs that currency | Factor in the formula | Effect on the index |
|---|---|---|---|---|
| EURUSD | +0.50% | 0.50% weaker | 1.005^(−0.576) = 0.997131 | −0.287% |
| USDJPY | +0.90% | 0.90% stronger | 1.009^(0.136) = 1.001219 | +0.122% |
| GBPUSD | −0.20% | 0.20% stronger | 0.998^(−0.119) = 1.000238 | +0.024% |
| USDCAD | +0.40% | 0.40% stronger | 1.004^(0.091) = 1.000363 | +0.036% |
| USDSEK | +0.50% | 0.50% stronger | 1.005^(0.042) = 1.000209 | +0.021% |
| USDCHF | +0.60% | 0.60% stronger | 1.006^(0.036) = 1.000215 | +0.021% |
Step by step:
- Multiply the six factors: 0.997131 × 1.001219 × 1.000238 × 1.000363 × 1.000209 × 1.000215 = 0.99937
- New index = 102.61 × 0.99937 = 102.55, a fall of 0.063%
- Check with the shortcut: 0.576 × 0.50 = 0.288 on the negative side, and the other five add up to about 0.225 on the positive side. The net is slightly negative, matching the calculation
The dollar strengthened against 5 of the 6 currencies. With equal weights, the dollar rose 0.35% on average, or 0.52% leaving the euro out. Yet DXY fell. Someone watching only DXY would conclude “the dollar is weak” when the truth is “the euro is strong”.
Why DXY mirrors EURUSD
The euro weighs 57.6%, and the pound, krona and Swiss franc mostly move in the same direction as the euro because their economies are tied together. So roughly three quarters of the index moves as one block with the euro. That is why a DXY chart and an upside-down EURUSD chart usually look almost identical.
Compare three scenarios with the same formula:
The middle row matters most. The euro falling 1% on its own (say, on European Central Bank news) lifts DXY by 0.58%, more than a day when the dollar strengthens 0.5% against every currency. If you see DXY jump and conclude “strong US data”, you may be wrong from the start.
DXY rising can mean a stronger dollar or a weaker euro. Check which before you conclude anything.
How to use DXY well
1. Separate a dollar story from a single-currency story. Compare your pair’s percentage move with DXY’s over the same period. If GBPUSD drops 0.8% while DXY barely moves, it’s a pound story. If DXY rises and every dollar pair moves the same way, it’s a dollar story, often from US data on the calendar. See How to read the economic calendar.
2. Always check two pairs first. EURUSD, because it is half the index, and USDJPY, because the yen is the second-largest weight at only 13.6%. When these two disagree, DXY will lean with the euro.
3. Build your own equal-weight basket. Take the dollar’s percentage move against several currencies and average them straight, like the +0.35% in the example above while DXY showed −0.063%. When those two numbers point in different directions, the euro has its own story going on. The same idea extends to measuring every currency’s strength in Currency strength meter.
4. Count your dollar exposure across the account. Holding Buy EURUSD, Buy GBPUSD and Buy gold at the same time is one bet that the dollar will weaken. On a day DXY spikes, every trade can hit its Stop loss together. How to count overlapping risk is in Correlation and portfolio risk.
DXY only tells you how far the dollar has already moved. It doesn’t predict where it goes next.
DXY and gold
Gold is priced in dollars worldwide. When the dollar strengthens, gold gets more expensive for holders of other currencies, so gold and the dollar tend to move in opposite directions. That is a tendency, not a law. Gold also moves with real interest rates, market fear and central bank buying, and there are periods when gold and the dollar rise together, for example when markets panic and people hide in both.
One more caution: to see how much gold moves against the dollar, comparing it with EURUSD or with DXY gives similar results, because DXY is mostly the euro anyway. And measure it on bar-by-bar returns, not on the shape of the price lines. How to measure it is in Correlation and portfolio risk. For rates and gold, read How interest rates move currencies and gold and Trading gold (XAUUSD).
The alternative: trade-weighted dollar indices
If you want to know whether the dollar is strong or weak “from the real US economy’s point of view”, there is another family of indices weighted by current trade (trade-weighted), such as the broad dollar index published by the US Federal Reserve. These include the currencies of many trading partners, including the Chinese yuan and the Mexican peso, and their weights are updated from time to time to follow trade.
The trade-off is that these don’t update tick by tick like DXY, and some currencies in the basket don’t float freely. They suit the big picture, not minute-by-minute reading during a trade. DXY is still the one most market participants watch on a chart. Which one to use depends on the question you want answered.
When DXY misleads
- European news. European Central Bank decisions or European data can move DXY sharply when nothing has happened to the dollar
- The yen running hard. USDJPY can move by large percentages, but DXY reflects only about a seventh of it
- The dollar moving against Asian or emerging-market currencies. They aren’t in the basket at all, so DXY can’t see it
- DXY charts that don’t match between sources. The index itself, futures and each broker’s CFD can differ slightly in price and trading hours. Check which one you are looking at
Common mistakes
- Thinking DXY is “the dollar against the world”. It is a basket of 6 currencies with weights frozen since 1973, and the euro takes more than half
- Using DXY to confirm a EURUSD signal. They are almost the same data upside down, so one adds nothing new to the other, the same problem as overlapping indicators in Combining indicators without redundancy
- Selling gold the moment DXY rises. Gold and the dollar often move opposite, but not every time, and DXY doesn’t say where price goes next
- Treating 100 as fair value. 100 is just the 1973 reference point
- Forgetting stacked dollar exposure. Several dollar pairs plus gold at once can be one bet, bigger than you meant
Frequently asked questions
Can you trade DXY?
The index itself is a calculated number. There are futures contracts based on it, and some brokers offer a dollar index CFD, with different specs, contract sizes and trading hours, so always check the contract specification first. Most retail traders use DXY as a lens rather than trading it.
If DXY rises, does gold have to fall?
No. Gold is priced in dollars, so it often moves against the dollar, but that is a tendency, not a law. There are periods when both rise together, for example when markets are scared and money hides in both. Measure the relationship on recent data yourself before relying on it.
Does a DXY level of 100 mean the dollar is fairly valued?
No. 100 is just the reference point set at March 1973 exchange rates. It only tells you how much stronger or weaker the dollar is than back then against this six-currency basket, not whether it is too expensive or too cheap.
This is general education, not investment advice. Trading is risky and you may lose all of your capital.