The Distribution Days Calculator calculates recent distribution days on a chosen index to gauge institutional selling and market pressure.
Report an issue
Spotted a wrong result, broken field, or typo? Tell us below and we’ll fix it fast.
About the Distribution Days Calculator
A distribution day is a session when a major index falls on higher volume than the prior session. It suggests professional selling pressure. Counting these days over a rolling period gives a quick read on supply and demand. Many traders watch the S&P 500, Nasdaq Composite, or a custom basket to spot stress building under the surface.
The Calculator automates this process. It scans daily closes and volumes, checks the decline threshold, and compares volume against the prior day. It then applies timing rules, such as expiring old signals after a set number of trading days or removing them when the index rallies strongly. You get a running total and a dated list you can review for scenarios like late-stage uptrends or early corrections.
This tool is designed for practical decisions. It helps you frame risk when adding exposure, trimming positions, or tightening stops. Whether you trade actively or rebalance quarterly, the count of distribution days offers an objective input to your process.
Equations Used by the Distribution Days Calculator
While the concept is simple, the Calculator relies on a few precise formulas to maintain consistency and remove bias. Here are the core equations it applies under the hood.
- Daily percent change: PercentChange = (Close[t] − Close[t−1]) / Close[t−1] × 100.
- Volume test: IsHigherVolume = Volume[t] > Volume[t−1]. A distribution day requires a decline and higher volume.
- Distribution day flag: IsDD = (PercentChange ≤ −Threshold%) AND IsHigherVolume. Default Threshold% is 0.2.
- Expiration rule: A distribution day recorded at day d expires after W trading days. Default W is 25.
- Rally reset: If the index rises R% above the close of a distribution day, that day is removed. Default R is 5.
- Optional stalling day: IsStall = (Close[t] ≤ Close[t−1]) AND (Intraday range shows upside rejection) AND IsHigherVolume. If enabled, stalls can count as distribution.
The Calculator applies these rules in sequence for each new bar and maintains a rolling count. Defaults reflect common practice, yet you can tune thresholds to fit your method. Adjustments affect sensitivity: lower thresholds catch more subtle selling, while higher ones filter noise.
The Mechanics Behind Distribution Days
Distribution tracks when supply overwhelms demand. A day of price decline on expanding volume hints that large sellers are active. A cluster of such days within a few weeks often precedes breakouts failing and larger drawdowns. The Calculator formalizes this signal so you can avoid relying on memory or ad hoc notes.
- Identify the index or basket you monitor and collect daily closing prices and volumes.
- Mark a day as distribution when price declines by at least the set threshold and volume exceeds the prior day’s volume.
- Optionally mark stalling days, when indexes finish flat to slightly down after trading higher, on increased volume.
- Keep a running window. Distribution days drop off after the window length, often 25 sessions.
- Remove a specific distribution day if the index rallies at least the reset threshold (commonly 5%) above that day’s close.
- Track the total count and the dates. Rising counts warn of potential trend breakdown and higher drawdown risk.
These mechanics align with well-known growth-investing playbooks. The count is not a forecast by itself. It is a stress gauge, best paired with relative strength, leadership quality, and breadth. Still, when distribution clusters, historical odds favor caution.
Inputs and Assumptions for Distribution Days
The Calculator accepts standard market data and a few simple options. Each input adjusts the signal’s sensitivity, so it’s important to understand what each one does and how it changes your scenarios and interpretation.
- Price series: Daily closing prices for your chosen index or watchlist aggregate.
- Volume series: Daily total volume for the same instrument or composite.
- Decline threshold (%): Minimum daily percentage drop to count distribution. Default 0.2%.
- Volume comparison: Use raw day-over-day comparison or an average-based test (optional).
- Window length (trading days): Number of sessions to keep in the rolling count. Default 25.
- Rally reset (%): Percentage increase from a distribution day’s close that removes it. Default 5%.
Reasonable ranges keep the signal practical. Thresholds under 0.1% may capture noise. Windows shorter than 15 days can swing too fast. If your index has irregular volume reporting, consider an average-volume comparison to smooth quirks. Half-days and holidays are recognized as valid sessions, but extremely low volume may reduce reliability.
Step-by-Step: Use the Distribution Days Calculator
Here’s a concise overview before we dive into the key points:
- Select your index or custom basket from the data menu.
- Upload or confirm daily close and volume data for the desired period.
- Set the decline threshold, window length, and rally reset options.
- Choose whether to include stalling-day logic in the count.
- Run the Calculator to generate the current count and date list.
- Review the breakdown by date, including which days have expired or were reset.
These points provide quick orientation—use them alongside the full explanations in this page.
Case Studies
Case 1: The S&P 500 is in an uptrend. Over 14 sessions, the index logs declines of −0.7%, −0.4%, −1.1%, and −0.3%, each on higher volume than the prior day. The Calculator, with a 25-day window and 0.2% threshold, counts four distribution days. No 5% rally above any of those days’ closes occurs, so none are removed. Interpretation: With four recent distribution days, risk of a failed breakout rises, and position sizing merits caution. What this means
Case 2: The Nasdaq Composite shows five distribution days in 20 sessions. Then a strong follow-through rally lifts the index 6% above the close of the earliest two distribution days. The Calculator automatically removes those two under the 5% reset rule, leaving three active. When the oldest remaining day ages past 25 sessions, it expires, dropping the count to two. Interpretation: Selling pressure eased. Exposure can be increased, but watch volume on up days to confirm accumulation. What this means
Accuracy & Limitations
Distribution counting is a rules-based way to read supply and demand, but it is not a guarantee. Market structure, volume sources, and index composition can skew readings. Treat the count as one input, not a complete system.
- Index changes and rebalances can alter volume patterns and trigger misleading spikes.
- Options expiration and index reconstitution days may inflate volume without true selling pressure.
- Holiday-shortened sessions can distort the day-over-day volume test.
- Different data vendors may adjust or revise volume after the close.
- ETFs can show volume unrelated to the underlying index’s breadth.
To improve accuracy, corroborate with breadth, leadership, and up/down volume ratios. Review individual components for confirmation. Above all, keep rules consistent; changing thresholds midstream reduces the value of historical comparisons.
Units & Conversions
Distribution analysis uses percentages for price changes and share counts for volume. Clear units keep your comparisons clean. Converting between percent and bps, or between millions and shares, prevents misreads when you run quick mental math.
| Unit | Conversion |
|---|---|
| Percent to bps | 1% = 100 bps; 0.2% = 20 bps |
| Decimal return to percent | 0.012 = 1.2%; −0.004 = −0.4% |
| Million shares to shares | 1 million = 1,000,000 shares; 2.5 million = 2,500,000 shares |
| Shares to standard lots | 1 lot = 100 shares; 25,000 shares = 250 lots |
| Dollar volume | Price × Shares; e.g., USD50 × 2,000,000 = USD100,000,000 |
| Trading days to weeks | 5 trading days ≈ 1 week; 25 trading days ≈ 5 weeks |
Use the table to translate raw data into the format your rules expect. For example, if your threshold is 20 bps, confirm that your daily change calculation expresses results in percent, not decimals, before comparing.
Tips If Results Look Off
If the count seems too high or low, small setup issues are often to blame. Walk through these checks before changing your rules or assumptions.
- Confirm your price series uses official closes, not last trade or midpoint.
- Verify volume is total composite volume and not a single venue.
- Check that your percent change uses the correct prior close.
- Ensure the window length and reset rules match your settings.
- Exclude known special events like rebalances when testing sensitivity.
After verifying inputs, run a short backtest period you can inspect by eye. Compare two or three known distribution days from a trusted source to confirm alignment.
FAQ about Distribution Days Calculator
What is a distribution day in simple terms?
It is a day when a market index closes down by at least a small threshold, and trading volume is higher than the previous session. This combination signals potential institutional selling.
How many distribution days are too many?
Context matters, but five or more within a 25-session window often signals rising risk. Traders may slow new buys or raise cash until the count falls.
Do stalling days always count as distribution?
No. Stalling criteria are stricter and optional. Many traders only count clear declines on higher volume, while others include stalls to capture subtle weakness.
Which index should I track?
Choose the index most aligned with your positions. Growth-focused investors often monitor the Nasdaq Composite, while broad portfolios may prefer the S&P 500.
Glossary for Distribution Days
Distribution Day
A session with a price decline at or beyond a set threshold and higher volume than the prior day, signaling potential institutional selling.
Accumulation Day
A session with a price gain and higher volume than the prior day, suggesting net institutional buying and positive demand.
Stalling Day
A session where an index trades higher intraday but closes flat or lower on increased volume, indicating upside rejection.
Rolling Window
The fixed number of trading days over which distribution days are counted before older entries expire.
Rally Reset
The rule that removes a past distribution day if the index rises a defined percentage above that day’s close.
Basis Points
A unit equal to 1/100 of a percent, used to express small percentage changes, such as 0.2% being 20 basis points.
Breakout
A price move above a notable resistance level, often on volume, signaling potential trend continuation.
Dollar Volume
Total traded value in money terms, computed as price times shares traded, useful for comparing liquidity across instruments.
Sources & Further Reading
Here’s a concise overview before we dive into the key points:
- Investor’s Business Daily: Understanding Distribution Days
- Nasdaq Market Data Glossary: Distribution Day
- Morningstar: What Is a Distribution Day?
- CFA Institute: Market Anomalies and Behavioral Finance
- William J. O’Neil: How to Make Money in Stocks (publisher page)
These points provide quick orientation—use them alongside the full explanations in this page.
Disclaimer: This tool is for educational estimates. Consider professional advice for decisions.