Study · re-run every night · updated Oct 15, 2026

Does a weaker dollar lift Bitcoin? The dollar index against Bitcoin, tested

The broad dollar index stood at 121.60 on Oct 9: +2.9% over the last 30 days (rising). On the 593 days since 2014 the dollar fell 1.5% or more in 30 days, Bitcoin bought at that day's close did +43.2% over the next 90 days on average, against +15.4% after the other days; on the 931 days it rose 1.5% or more, +8.0%. No band is clear of luck (a luck test of 3 with both halves of the days agreeing): the dollar moves in long swings, and a few of them decide the averages. Past patterns, not financial advice.

The dollar index

121.60

Oct 9

Last 30 days

+2.9%

rising

After a falling dollar

+43.2%

Bitcoin, the next 90 days

Every day

+19.0%

Bitcoin, the next 90 days

First written Oct 15, 2026 · 1 revision

§ 01 · Today

Today's dollar

as of Oct 15, 2026 · The Fed's broad dollar index, Feb 3, 2014 to Oct 14, 2026

"When the dollar weakens, Bitcoin rallies", the macro saying goes: a cheaper dollar sends money looking for things that hold value, and Bitcoin is priced in dollars. Here the dollar is the Federal Reserve's own broad dollar index (the dollar against the currencies of the US's trading partners, from FRED), its change over the last 30 days on each day, and every such day is a buy of Bitcoin at that day's close, held 30 or 90 days.

Oct 9, 2026: 121.60, +2.9% over the last 30 days: rising.

the dollar index (a log scale; its 30-day change on hover)

§ 02 · After it

What came after it

as of Oct 15, 2026 · Bitcoin, from the reading day's close

Bitcoin's average next 90 daysevery day's averageunder each bar: its days

The dollar, 30 days	Days	Stretches	Next 30 days	Next 90 days
falling −1.5% or less	604	57	+9.1%	+43.2%
easing −1.4% to −0.1%	1,572	91	+4.7%	+22.0%
firming 0% to 1.4%	1,500	97	+6.0%	+13.3%
rising 1.5% or more	931	58	+3.4%	+8.0%
every day	4,607	—	+5.4%	+19.0%

Days and stretches count the days with 30 days after them; a stretch ends after 7 days out of its band. Today's band is marked. Each band against all the other days over the same hold, with its luck test under it (✓ past the bar, both halves of the days agreeing; the halves on hover):

The dollar, 30 days	Next 30 days	Next 90 days
−1.5% or less	+4.2% t 1.2	+27.8% t 2.5
−1.4% to −0.1%	−1.2% t −0.5	+4.5% t 0.8
0% to 1.4%	+0.8% t 0.4	−8.5% t −1.5
1.5% or more	−2.5% t −0.8	−13.9% t −1.6

A falling dollar (−1.5% or less in 30 days) came on 593 days in 55 separate stretches, the last on Aug 30, 2026. Bitcoin bought at the close of one of those days rose over the next 90 days 82% of the time (+27.7% in the middle case, +43.2% on average): +27.8% against the other days, +36.9% in the older half of the days and +23.0% in the newer. A luck test of 2.5, not past the bar of 3.0: 21 holds that share no day, and a few big swings decide the average.

A rising dollar (1.5% or more in 30 days) came on 931 days in 58 separate stretches, the last on Oct 14, 2026. Bitcoin bought at the close of one of those days rose over the next 90 days 47% of the time (−2.5% in the middle case, +8.0% on average): −13.9% against the other days, −17.2% in the older half of the days and −11.4% in the newer. A luck test of −1.6, not past the bar of 3.0: 25 holds that share no day, and a few big swings decide the average.

§ 03 · How it is tested

How it is tested

as of Oct 15, 2026 · methodology

A luck test (t) says how far a result sits from zero, in units of its own noise: about 2 is rarely luck for one test, but many tests at once need more, which is what the first cut is for.

FRED publishes a day's index a day or two after it, so each close reads the newest reading dated at least two days before it, and the change is set against the reading known 30 days before that: nothing read early. Neighbouring days share most of their 30 or 90 days, so the luck test does not count them as fresh evidence: each calendar day weighs in by how many of the band's holds, and of the other days', cover it, so a band counts as the holds that share no day, and each band is set against all the other days over the same hold, which takes out the years Bitcoin simply rose. With 8 tests (four bands, two holds), a result needs a luck test of 3.0 or more and both halves of the days on its side.

The bands were set before any number here was read: falling (1.5% or more down in 30 days), easing, firming, rising (1.5% or more up) - about one month's usual swing of the index either way. The dollar moves in long swings, so its ends come in a few long stretches. Moves are Bitcoin's own price, before trading costs.

§ 04 · Revisions1 dated

Revisions

as of Oct 15, 2026 · every change to its headline numbers, dated

This study is re-run every night on the whole history: Bitcoin's daily closes from Jan 1, 2014 to Aug 16, 2017 are Bitstamp's, Europe's oldest exchange, and ours from the next day on (on the 3,346 days both have, the two closes differ by 0.06% in the middle case). It was first written on Oct 15, 2026; its numbers last moved on Oct 15, 2026. Each night its headline numbers moved is listed here, newest first.

Oct 15, 2026Bitcoin over the next 90 days against the other days: after a falling dollar +28% · after a rising dollar −14%

§ 05 · More

More research

as of Oct 15, 2026