Volume Anomalies: The Earliest Signal That Smart Money Is Moving

4-section structure: Concept / How We Compute / How to Read / Caveats.

1. Concept

Price is the outcome, volume is the cause. Institutional money cannot enter without leaving volume footprints.

Volume anomaly: today's volume is unusually high (≥ 2× the 20-day average) — signals large block buying or selling
52-week high: today's close sets a new 1-year high — buyers completely absorbed overhead supply
52-week low: today's close sets a new 1-year low — sellers crushed all bid support
A/D Ratio: advancing / declining stocks — measures market breadth

These 4 signals are often more timely than charts — MAs, MACD, KD are lagging indicators, while volume and new highs/lows are coincident or even leading indicators.

2. How We Compute

2.1 Volume Anomaly

volume_ratio = today_volume / mean(vol_20d_excluding_today)

Denominator: average over past 20 trading days (estimated via 30 calendar days) excluding today
Threshold: default ×2.0 (today's volume = 2× the 20-day average)
Site offers 4 quick thresholds: ×1.5 / ×2.0 / ×3.0 / ×5.0

Sample requirement: at least 10 trading days in the past 20 (to filter out newly-listed stocks with insufficient history).

2.2 52-Week High / Low

new_high = today_close >= max(close_252d) × 0.995
new_low  = today_close <= min(close_252d) × 1.005

252 trading days ≈ 380 calendar days
±0.5% tolerance: avoids floating-point misses and technical gaps (e.g., missing a new high by 2 cents)

Sample requirement: at least 100 trading days in the past year.

2.3 A/D Ratio

A/D Ratio = advances / declines

advances: stocks with chg_pct > 0 today
declines: stocks with chg_pct < 0 today
Typically: A/D > 1.5 → broad rally; A/D < 0.67 → broad selling; near 1.0 → divergence

2.4 Caching Strategy

Whole ranking @cached(ttl=3600) (1-hour cache):

Intraday (09:00-13:30): refreshes hourly to reflect latest volume changes
After close: results are fixed, no need for repeated computation

3. How to Read

3.1 Volume × Direction: 4 Quadrants

Volume	Change	Meaning	Next Step
×5+	+5%+	Volume-up surge — aggressive institutional buying or news catalyst	Verify news, watch next-day continuation
×5+	−5%+	Volume-down plunge — institutional selling or bad news	Warning — don't chase the bounce
×2~5	Mild up	Volume up, price up — healthy bull signal	Hold / enter
×2~5	Mild down	Volume up, price down — watch for reversal, possible ownership change	Watch 3-day bounce
×2+	±1%	Volume spike with no direction — heavy ownership rotation at the same price	Danger signal (possible top or bottom pivot)

3.2 Statistical Meaning of New Highs / Lows

In a trending market:

Bull market: new highs : new lows = 10:1 or higher
Bear market: new highs : new lows = 1:10 or lower
Turning point: new highs suddenly drop from 50 → 5, new lows jump from 5 → 50 is a classic warning

The header shows:

52-week new highs count / % of market
52-week new lows count / % of market

Above 5% of the market = clear strong / weak signal.

3.3 Reading A/D Ratio

A/D Range	Market State	Color
≥ 1.5	Broad rally	Deep red
1.0 ~ 1.5	Bullish divergence	Light red
0.67 ~ 1.0	Bearish divergence	Light green
< 0.67	Broad selling	Deep green

Critical application: index +1% but A/D = 0.8 → index pulled up by a few large-caps; most stocks are actually falling → breadth is actually weak.

3.4 Cross-Reading

Volume spike + new high: strongest signal, institutional breakout confirmed
Volume spike + new low: weakest signal, stop-loss cascade or bad news
Volume spike + small chg_pct: ownership rotation within range, watch for direction
New highs >> new lows + A/D > 1.5: clear bull market
Both new highs and lows high + A/D ≈ 1: polarized market, stock-picker's market

4. Caveats

⚠️ Volume Ratio Is Relative, Not Absolute

×5.0 on a typically-quiet stock is more meaningful than ×5.0 on a daily-hot stock. Quiet stocks have low daily volume, so ×5 may still be 1% of an active stock. Always cross-reference with absolute volume (in millions).

⚠️ Ex-Dividend / Rights Days Cause False Signals

The reference price auto-drops on ex-dividend day. Even if the stock actually gains, the displayed chg_pct may be negative (unadjusted). New-low lists may mis-flag ex-dividend stocks.

Mitigate: currently unadjusted — if a stock "suddenly crashes to new low," verify whether it's ex-dividend day.

⚠️ New-Low List Explodes in Bear Markets

During 2024/8 crash, 2020/3 COVID, 300+ stocks may hit 52-week lows in one day. List only shows top 30 (worst-performing). Full list requires advanced query.

⚠️ Recently-Listed Stocks Lack Reference Period

Stocks listed < 252 trading days won't appear in new-highs/lows (insufficient sample). Some newly-listed small-caps may be missed.

⚠️ A/D Ratio Excludes Unchanged Stocks

Stocks with 0 change aren't counted. On very quiet market days with many non-traded stocks, A/D Ratio may be skewed.

⚠️ Volume "20 Days" Is Calendar-Day Approximation

Uses 30 calendar days ≈ 20 trading days (strict SQL window is expensive). After long holidays (Lunar New Year, national holidays), the average has slight baseline drift.

⚠️ Excludes After-Hours and Odd-Lot Volume

"Today's volume" only includes regular-session matched trades. Large-caps' true volume may be understated 10-20%.

Try It

Open Anomaly Signals, toggle volume thresholds ×1.5 / ×2 / ×3 / ×5
On strong days, check if A/D > 1.5 and new-highs % > 5%
On weak days, see which sectors dominate the new-low list (often a leading indicator)
Find a stock with ×5+ volume ratio, click through to see if the chart shows a volume-price breakout
Click 📐 for formulas, sample requirements, 52-week tolerance settings