LY Traders · 29 October 2026
A study circulating among analysts makes a tidy claim: a stock index's daily
move, measured open to close, stays within ±0.5% about 75% of the time.
Bigger than ±0.75% on only 5% of days. Bigger than ±1.2% on just 1%. If that
were true, trading an index would have a shape you could plan around — a
normal envelope with rare surprises.
We run automated trading systems on four major indices every day: Japan's
Nikkei 225, Hong Kong's Hang Seng, the US Nasdaq 100 and the US Russell 2000.
So we did what we always do with a borrowed number — we tested it. Same
method as the claim: open-to-close only, no intraday extremes. 1,833 trading
sessions, January 2025 to October 2026, Investing.com daily data.
The claim does not survive. But what the data actually shows is more useful
than either the myth or its debunking — because it confirms the first half of
the intuition while destroying the second.
The intuition behind the 75% claim is sound. Most trading days are, in fact,
quiet. Across our four indices, 53–60% of sessions stay within ±0.7%
open-to-close, and 40–50% stay within ±0.5%. The median day moves just
0.51–0.64%. Sit at a screen for a week and this matches your eyes: price
sloshes inside a range, fills orders, goes home.
This is not nothing. It is why range-aware systems have a job, and why the
~40% of days that round-trip inside ±0.5% are exactly where intraday systems
bleed commissions and spread for nothing. The range day is the rule. That
part of the folklore is honest.
Here is where the study falls apart. The 75% claim says a ±1.2% day happens
on 1% of days — roughly two or three times a year. Our data:
1%. More than one day in five.
claim calls "normal".
A rule of thumb that misses the frequency of big days by a factor of twenty
is not a rule of thumb. It is a different market's weather forecast.
The single biggest open-to-close move we measured is 11.85% on the Nasdaq
100: 9 April 2025, the tariff-crash rebound (−4.8% on 4 April, −5.2% on 8
April, then +12% in one session). The Russell 2000's largest day is 9.75%.
These are not bad data points to be cleaned out. They are the days that
define the year for anyone trading these markets, and the borrowed study
prices them at two or three per century.
We re-ran the counts by half-year. On the Nikkei, the share of days moving
more than ±1.5% tripled from 6.7% in the first half of 2025 to 20.8% in the
first half of 2026. Meanwhile Hang Seng, Nasdaq and Russell cooled off —
67–69% of their recent sessions sat inside ±0.7%, while the Nikkei stayed hot
at 51%.
So the honest version of "most days are range days" is conditional: most
days are range days in a calm regime, and the boundary between regimes is
neither fixed nor announced. Any "N% of days" statistic without a market and
a date range attached is close to meaningless — the number is a property of a
period, not a law of markets.
Everything above is measured on our own trading markets; none of it is
advice. Three things follow from the distribution itself:
target assumes ±0.5% is the envelope, it is set at the median day's entire
open-to-close range. Half of all days blow through it; one day in five gaps
far past it.
versus "trend week" rhythm everyone notices in their own results is this
distribution playing out — 40% of days give back everything to costs, and
roughly one day in five pays for the whole stretch. Our own Hang Seng
book's best week this quarter drew +17.9% of its quarter-to-date profit
from exactly one crash fortnight.
week — 20–23 Nikkei days beyond ±1.2% per weekday. You cannot schedule
around them; you can only size so that they are survivable, and ideally
the days your system is built to harvest.
Open-to-close understates true intraday range — a day that whipsaws 2% and
closes 0.3% up counts as quiet in this method. We chose it to match the
claim we were testing, not because it captures real risk; high-to-low ranges
are materially larger. And 2025–2026 contains an unusually volatile stretch,
so a study over a calmer decade would show thinner tails. That is precisely
the point. Data source: Investing.com daily history; figures may be
reproduced with attribution to Investing.com. This is a description of
measured distributions, not investment advice.
The market changes. The rules don't.
