What the dollar index is

A currency has no price of its own. It only has exchange rates against other currencies, and on any given day the dollar can be up against the yen and down against the euro. A dollar index solves that by averaging many exchange rates into a single number. When the index rises, the dollar buys more foreign currency than before. When it falls, it buys less.

The one most people mean is the US Dollar Index, ticker DXY, maintained by ICE (Intercontinental Exchange). It compares the dollar with six currencies, using weights that have changed only once, when the euro replaced several European currencies in 1999:

CurrencyWeight in DXY
Euro57.6%
Japanese yen13.6%
British pound11.9%
Canadian dollar9.1%
Swedish krona4.2%
Swiss franc3.6%

The index is a weighted geometric average measured against a base of 100 set in March 1973, shortly after the dollar began to float freely. A reading of 98 means the dollar is about 2% weaker against this basket than it was then.

Notice what is missing. China, Mexico, South Korea and India, among the largest US trading partners, have no weight at all. More than half of DXY is simply the euro. That is why some analysts call it a euro index turned upside down.

The other dollar index: the Fed's broad index

The Federal Reserve publishes its own measure, the nominal broad dollar index. It covers 26 currencies, chosen because each accounts for at least 0.5% of US trade, and its weights follow actual trade flows and are updated every year. It is set to 100 in January 2006. FRED carries the daily series as DTWEXBGS, and it is the series we use for our measurement below.

The largest weights for 2026, as published by the Fed:

EconomyWeight in the broad index, 2026
Euro area21.0%
Mexico14.8%
Canada12.8%
China10.9%
United Kingdom5.2%
Japan5.2%

When the two disagree: the first half of 2025

The difference is not academic. In the first half of 2025, DXY fell about 10.7%, its worst first half since 1973, as widely reported at the time. Over the same six months the broad index fell from 129.28 to 119.41, a drop of 7.6% (our calculation from FRED). The euro, the yen and the Swiss franc all gained more than 10% against the dollar, and those currencies dominate DXY. The peso and the yuan, which matter far more in the broad index, moved less.

Rule of thumb: DXY tells you how the dollar is doing against other rich-world currencies, which is what most traders watch. The broad index tells you how the dollar is doing against the world it actually trades with.

How to read a dollar index

Direction first, level second. A level of 120 on the broad index means nothing on its own. What matters is the change over weeks and months.

Scale your expectations. Currencies move slowly compared with crypto. On our data since 2017, the broad index has a typical weekly move (standard deviation) of 0.70% and a typical monthly move of 1.57%. Bitcoin's are 9.33% and 20.25%, about 13 times larger. So a 1% month for the dollar is a notable month, and a 3% month is rare: it has happened only six times in 108 months.

Ask why it moved. The dollar usually rises for one of two reasons. Either US interest rates are expected to rise relative to other countries, which pulls money into dollar assets, or investors are frightened and run to the safest cash they can find. Both are bad for risk assets, but for different reasons. The dollar falls when the reverse happens, or when confidence in US policy itself is shaken, as in 2025.

Where the dollar stands now

Key levels of the broad index from FRED, with the dates they were reached:

PointDateBroad index
2021 lowJun 1, 2021110.50
2022 peak, Fed hiking fastSep 26, 2022128.45
Highest since 2006Jan 13, 2025130.04
Low after the 2025 slideJan 29, 2026117.44
Latest availableSep 25, 2026120.33

So the dollar is about 7.5% below its January 2025 peak, a little above its January 2026 low, and up just 0.49% since the end of 2025. After a big fall, it has spent 2026 mostly going sideways. The Fed's next H.10 release is due this afternoon, Monday October 5, at 4:15 p.m. New York time.

Why the dollar should matter to Bitcoin

Bitcoin is quoted in dollars almost everywhere, so a weaker dollar mechanically lifts the dollar price of anything priced globally, a bit like gold. That effect is small, because currencies move so little.

The bigger channel is money conditions. A strong dollar usually comes with high US interest rates, which make holding an asset that pays no yield more expensive, and it tightens financing for borrowers around the world who owe dollars. A falling dollar tends to come with the opposite: easier money and more appetite for risk. We covered the interest rate side of this in our real interest rates explainer.

That is the theory. Now the data.

Our measurement: 475 weeks of the dollar and Bitcoin

We took the Fed's broad dollar index from FRED and Bitcoin's daily close on Binance (BTCUSDT), and measured Friday to Friday changes from August 2017 to September 25, 2026: 475 weeks. We used weekly rather than daily changes because the Fed records exchange rates at noon New York time while Bitcoin's daily candle closes at midnight UTC, and daily figures would mix up the timing. All numbers in this section are our calculations.

The correlation of weekly changes over the whole period is minus 0.175. Negative means they tend to move in opposite directions. But it is small. Squared, it says dollar moves explain about 3% of Bitcoin's week to week swings. The other 97% is everything else.

YearWeeksCorrelation of weekly changes
201852-0.13
201952-0.17
202052-0.37
202153-0.17
202252-0.30
202352-0.07
202452-0.06
202552-0.33
2026, to Sep 2539-0.24

What stands out is how consistent the sign is. We also calculated the correlation over every rolling 52-week window. It was negative in 406 of 424 windows, or 95.8%. The most negative was the year ending March 13, 2020, the week of the pandemic crash, at minus 0.53. The highest was only plus 0.04, in February 2024. The latest window, ending September 25, 2026, reads minus 0.27.

The link gets stronger in years of stress (2020, 2022, 2025) and almost disappears in calmer years (2023, 2024). That fits the idea that the dollar matters most for Bitcoin when big macro forces are driving both at once.

A strong dollar hurts more than a weak dollar helps

Correlation hides the shape of the relationship, so we also sorted every calendar month from September 2017 to August 2026 (108 months) by how much the broad index moved, and looked at Bitcoin in the same month. Our calculation:

Dollar that monthMonthsBitcoin medianBitcoin rose
Rose more than 1%35-5.9%12 of 35 (34%)
Moved less than 1% either way42+8.5%28 of 42 (67%)
Fell more than 1%31+2.8%17 of 31 (55%)

Read that table slowly, because it is not what the slogan predicts. A sharply rising dollar has been a real headwind: Bitcoin lost ground in about two of every three such months. But a sharply falling dollar was close to a coin flip, and Bitcoin's best months came when the dollar barely moved at all.

The extreme months show why. In March 2020 the dollar jumped 4.1% and Bitcoin fell 24.8%, both driven by the same pandemic panic. In April 2025 the dollar fell 3.2% and Bitcoin rose 14.1%, the slogan working as advertised. But in November 2022 the dollar also fell 3.2%, and Bitcoin dropped 16.2% anyway, because that was the month the FTX exchange collapsed. A crypto-specific shock beats a friendly dollar every time.

Across all 108 months, the dollar and Bitcoin moved in the same direction 48 times and in opposite directions 60 times. The dollar tilts the odds a little, and that is about all.

How to use the dollar index without fooling yourself

  1. Watch weeks and months, not hours. The dollar's daily moves are tiny next to Bitcoin's, and our weekly correlation is already weak. On a daily chart, any overlap is mostly coincidence.
  2. Treat a strong dollar month as a warning light. It has been the worse environment for Bitcoin in our sample, especially when the cause was rising US rates or a scramble for safety.
  3. Do not treat a falling dollar as a buy signal. In our data it raised Bitcoin's odds only a little above even.
  4. Check which index you are looking at. A headline about DXY is mostly about the euro. If the story is about trade, tariffs or emerging markets, the broad index is the better gauge.
  5. Look for the shared cause. When the dollar and Bitcoin move hard at the same time, something bigger, like a Fed decision or a market panic, is usually driving both. Our Fed meeting explainer covers the main one.

Limits of this measurement

Correlation is not causation, and a 3% share of explained variation is a reminder of how much else moves Bitcoin. Our sample starts in August 2017, when Binance's BTCUSDT data begins, so it covers one long cycle of US interest rates rather than many. BTCUSDT is priced in the Tether stablecoin, which tracks the dollar closely but is not the dollar itself. And we used the Fed's broad index, not DXY, because the Fed's series is free and public. The two move together most of the time, but as 2025 showed, not always by the same amount.