Raw share counts are useless for comparison. A stock trading 40 million shares means nothing until you know what it usually trades.
About the Numbers in This Tutorial
The figures below were measured on SPY in July 2026, across the full price history the tool loads. Numbers like these move slowly, since each new session is one more observation in a very large sample, so expect small differences rather than different conclusions.
The multiple
Every session gets a volume multiple: its volume divided by the average volume of the previous 30 sessions.
multiple = today's volume ÷ average volume of the prior 30 sessions
A multiple of 1.0 is a perfectly ordinary day. 2.0 means twice the recent norm.
The day is excluded from its own baseline
This is the detail that makes the number trustworthy. The 30-session average is taken from the days before the one being measured, never including it.
If a spike were allowed into its own denominator it would inflate the average it is being compared against and quietly shrink its own multiple. Excluding it means a 3× day is measured against a normal baseline rather than one it distorted.
Today is compared against a baseline it played no part in building.
The tool has no fixed definition of a volume spike. You set the bar, and the whole page recalculates around it.
Two modes
Greater Than is open ended: every session at or above your multiple counts. Range adds an upper bound so you can study a band, for example days between 1.5× and 2×, without the truly extreme sessions dragging the averages.
The multiple is adjustable from 0.1× to 10× in steps of a tenth.
Auto-detect
By default the tool seeds the threshold from the latest session's own multiple, so the page opens describing days like today. The Auto-detect Volume switch turns that off when you want to hold a level steady while changing tickers, and Reset to Last Volume Multiple returns you to it.
Worth knowing when the opening view surprises you: a quiet session seeds a low threshold, which is why the tool can open showing thousands of matches rather than a handful.
A Rounding Detail
Thresholds live on a one-decimal grid, and matching happens on that same grid. A session whose raw multiple is 2.66 displays as 2.7 and counts at a 2.7 threshold. Without that, the auto-detected level would round the very session that produced it out of its own results. The log still shows the true 2.66, so a boundary row can read 2.66 under a 2.7 heading.
Chapter 3
The Two Columns
Matching sessions are split by the day's own direction: green if it closed above the prior close, red if below. Each side gets its own count and its own forward statistics.
Volume is not evenly distributed between them
This is the first real finding, and it emerges the moment you raise the threshold:
Threshold
Green days
Red days
Green share
0.5× (near enough every session)
2,699
2,232
55%
1.5×
169
380
31%
2.3×
21
58
27%
Measured on SPY, 21 July 2026.
At ordinary volume SPY closes green more often than red, which is what an instrument that rises over time should do. Raise the bar and it inverts completely: at 1.5× volume, more than two thirds of the matching sessions are down days.
Heavy volume is not a neutral marker of interest. It is concentrated in selling. Buying tends to be patient and distributed; selling arrives all at once, and the volume record shows it.
What This Means for Reading the Page
The two columns are never comparable in size at a high threshold, and the green column thins out fastest. By 2.3× on SPY there are only 21 green sessions in the whole record. Treat that column's percentages accordingly.
Under each column, forward performance measured from that session's close at the next day, the next 5 and the next 10 trading days, each with green/red odds and the average up-move and down-move separately.
The heavy-volume up day behaves differently
Threshold
Next day after a GREEN day
Next day after a RED day
0.5× (near enough every session)
54% green
56% green
1.5×
43% green
57% green
2.3×
43% green
52% green
Measured on SPY, 21 July 2026.
Read the middle column downward. At ordinary volume, the day after an up day is green 54% of the time, in line with the market's usual drift. At 1.5× volume that falls to 43%, meaning the session after a heavy-volume up day was more often down than up.
The right-hand column barely moves. Heavy-volume down days were followed by roughly the same odds as ordinary ones.
So the asymmetry sits entirely on the green side. A big up day on big volume looked more like exhaustion than confirmation, at least on this ticker over this history.
Read the average moves alongside the odds
The odds and the magnitudes answer different questions. At 2.3×, the day after a heavy-volume red session was green 52% of the time, with the up moves averaging +2.23% against down moves of −1.42%. Slightly better than a coin flip on direction, and meaningfully larger when it went the right way.
Neither number is worth much alone. A 52% win rate with wins half the size of losses is a poor arrangement, and the page gives you both precisely so you do not have to guess.
Chapter 5
The Baseline Trick
Most tools of this kind tell you what follows an event and leave you guessing what ordinary looks like. This one can tell you both, and the method is not obvious.
Set the threshold low
Drop the multiple to 0.5× and almost every session in the history qualifies. On SPY that is 2,699 green days plus 2,232 red days, which is very nearly the entire record.
At that point the tool is no longer describing volume spikes. It is describing the ticker's ordinary behavior: how often an up day is followed by another up day, what the average moves look like, how the 5 and 10 day horizons resolve.
That is your baseline. Raise the threshold back to the level you actually care about and every figure now has something to be compared against.
Why This Matters So Much
Without a baseline, "43% green the next day" is just a number. Against a 54% baseline from the same ticker over the same history, it becomes an 11-point gap, which is the entire finding of Chapter 4. The comparison is what carries the meaning, and this tool is unusual in letting you generate both halves of it yourself.
Two cautions
A 0.5× threshold is not literally every session, so the baseline is very slightly biased toward days with at least some participation. On a liquid ticker the difference is negligible; on a thin one it may not be.
And the baseline is per ticker. Do not carry SPY's 54% across to a small cap, a leveraged ETF or a commodity fund. Regenerate it for whatever you are looking at, which takes one adjustment of the stepper.
The tool has its own guided walkthrough if you want the controls pointed out on the live page: