Direct Answer
Positive Volume Index (PVI) is a cumulative indicator that only updates on days when volume rises from the prior day: on those days, it moves by the same percentage as price; on flat- or falling-volume days, it carries forward unchanged. The traditional framing compares PVI with its own long-term moving average, commonly around 255 periods, with PVI trending above that average traditionally read as a mildly bullish backdrop. That reading is a dated, debated heuristic, not a proven predictive rule.
Key Takeaways
- PVI only recalculates on rising-volume days; on flat or falling-volume days, it simply carries the prior value forward unchanged.
- On a qualifying day, PVI moves by the same percentage change as price. It is scaled by percentage return, not by adding raw volume the way On-Balance Volume does.
- The indicator is associated with Paul Dysart and later popularized by Norman Fosback, who framed PVI against its own long-term moving average, commonly around 255 periods.
- PVI trending above that moving average has traditionally been read as a mildly bullish backdrop, a dated, debated heuristic, not a validated predictive signal.
What Is the Positive Volume Index?
The Positive Volume Index (PVI) is a cumulative indicator built on a simple filter: it only changes on days when volume is higher than the prior day. The premise behind the original framing was that price action accompanying rising volume might reflect participation from a broader base of traders, sometimes framed historically as "the crowd", rather than the quieter positioning of a smaller group. That framing predates modern market structure and should be treated as historical context, not an established mechanism.
Because PVI only updates on rising-volume days and holds flat otherwise, its line traces the cumulative effect of price changes specifically on the days when participation was increasing, while ignoring what happened on quieter, lower-volume days entirely.
Key takeaways: PVI is a cumulative index that recalculates only on rising-volume days, moving by that day's percentage price change; on flat- or falling-volume days it carries the prior value forward unchanged. It is associated with Paul Dysart and later Norman Fosback, who compared PVI with its own long-term moving average, commonly around 255 periods. PVI trending above that average has traditionally been read as a mildly bullish backdrop, a dated, debated heuristic rather than a proven predictive rule.
The Formula
Rule: compare today's volume with yesterday's volume.
- If Volumetoday > Volumeyesterday: PVItoday = PVIyesterday + PVIyesterday × ((Closetoday − Closeyesterday) ÷ Closeyesterday)
- Otherwise: PVItoday = PVIyesterday (unchanged)
In words: on a day when volume increases from the prior day, PVI moves by the same percentage that price moved. On a day when volume is flat or lower than the prior day, PVI does not change at all, regardless of how price moved that day. The series is typically started at an arbitrary base value, such as 100 or 1,000, the starting number itself has no significance, since only the line's percentage change and its relationship to its own moving average are interpreted.
Worked Example
Hypothetical example, for education only.
Assume PVI starts at a base value of 100.00 on Day 1.
| Day | Close | Volume | Volume vs. prior day | PVI |
|---|---|---|---|---|
| 1 | $50.00 | 1,000,000 | N/A | 100.00 (base) |
| 2 | $51.00 | 1,200,000 | Higher | 100.00 + 100.00 × ((51.00 − 50.00) ÷ 50.00) = 102.00 |
| 3 | $49.50 | 950,000 | Lower | Unchanged = 102.00 |
| 4 | $49.00 | 1,050,000 | Higher | 102.00 + 102.00 × ((49.00 − 49.50) ÷ 49.50) = 100.97 |
Day 3's price drop is never reflected in PVI, because volume fell that day, the rule only looks at price change on days when volume rose. Day 4 shows PVI moving lower even though the prior day's PVI value was unaffected by Day 3's decline, because Day 4 itself was a rising-volume day with a negative price change. This is the mechanism by which PVI can diverge from a simple cumulative price return: it selectively captures price change only on rising-volume days, in either direction.
How PVI Is Commonly Used
PVI versus its own long-term moving average
The traditional framing, associated with Paul Dysart and later popularized by Norman Fosback, doesn't treat individual day-to-day PVI moves as trade signals. Instead, it compares the PVI line with its own long-term moving average, commonly around 255 periods, roughly a year of daily data. PVI trending above that moving average has traditionally been read as a mildly bullish backdrop; PVI trending below it, the reverse. This is a dated, debated heuristic rooted in mid-20th-century market observation, not a proven predictive rule, and it should not be treated as a standalone trading system.
Trend and slope of the PVI line itself
Independent of the moving-average comparison, some traders simply watch whether PVI is trending up or down over a given stretch, treating a rising line as a description of price behavior specifically on higher-volume days. Because the indicator ignores falling-volume days entirely, its slope reflects a narrower slice of the price history than a simple price chart does. It is not a complete substitute for looking at price directly.
Pairing with its counterpart, Negative Volume Index
PVI is commonly discussed alongside its counterpart, the Negative Volume Index (NVI), which applies the same mechanism to falling-volume days instead. The two indicators answer different questions about which volume regime accompanied a given price move, and comparing them is a common extension of the traditional framework rather than a separate, unrelated tool.
The Moving Average Period
PVI itself has no lookback parameter. It is a pure running total gated by the volume comparison. The one commonly varied setting is the length of the moving average PVI is compared against.
| MA period | Approximate span | Common framing |
|---|---|---|
| ~255 periods | ~1 trading year | The traditional Dysart/Fosback framing |
Exact defaults vary by charting platform, so verify the moving average length and smoothing method (simple or exponential) your platform actually uses before comparing readings across sources.
Why PVI Produces False Signals
- The underlying heuristic is dated and debated. The PVI-above-MA reading traces back to mid-20th-century market observation and has not been established as a reliable forecasting method under modern market structure, liquidity, or trading behavior.
- It ignores every falling-volume day entirely. A large price move on a quieter volume day contributes nothing to PVI, so the line can understate or misrepresent what actually happened to price over a given stretch.
- The volume-comparison rule is a simple day-over-day threshold. A single unusually low-volume day, followed by an ordinary day, can register as a "rising volume" day and trigger a PVI update that has little to do with genuine participation change.
- Volume reporting varies by data source. Consolidated-tape versus single-venue volume figures can differ, and that difference can flip whether a given day counts as "rising" or "falling" volume in the calculation.
Common Mistakes
- Treating PVI above its moving average as a standalone buy signal. The traditional framing describes a backdrop, historically, not a trade trigger, it needs a price-based entry, invalidation, and position size to become an actual trade.
- Assuming the heuristic has been validated under current market conditions. It's a dated, debated observation, not a rule proven to hold up across modern instruments and regimes.
- Comparing raw PVI values across different instruments. The starting base value is arbitrary, so absolute PVI levels aren't comparable between two different stocks or assets, only the line's trend and its relationship to its own moving average are meaningful.
- Ignoring how falling-volume days are handled. Because PVI carries forward unchanged on those days, a trader who doesn't understand the rule can misread a flat stretch of the line as "no price movement" when price actually moved on lower volume.
- Mixing moving-average periods or smoothing methods across platforms. A 255-period simple moving average and an exponential variant of similar length can diverge meaningfully, confirm which one a given chart is showing before comparing it with another source.
Limitations
PVI is built entirely from historical closing prices and volume, it has no awareness of fundamentals, order-book depth, news, or forward-looking information. Its core premise, that rising-volume price moves are more meaningful than falling-volume price moves, is a long-standing but unproven assumption rather than an established fact. The traditional PVI/moving-average heuristic in particular is dated and debated: it has not been demonstrated as a reliable, forward-looking signal under modern market conditions, and it should be treated as historical context for how the indicator was originally used rather than a validated trading rule.
Following the Days When Everyone Showed Up
The Positive Volume Index updates only on sessions where volume rose, on the premise that heavy days reflect broad participation rather than informed positioning. It is the mirror of its companion indicator and rests on the same era's reasoning about who trades when.
The intended use is comparative, running it alongside its counterpart and reading the difference between what the busy days and the quiet days are doing. Where they diverge over long windows, the divergence is the output, and neither series carries much on its own.
The mistake is applying either as a short-term signal. Both update on a subset of sessions, which makes them slow by construction, and a series that skips days produces a line whose turns lag price by more than its appearance suggests.
The premise itself is also weaker than when the indicator was devised. High-volume sessions in current markets frequently reflect index events, derivative expirations and rebalancing flows, all of which are mechanical rather than expressing any view about the security.
PVI FAQs
What does PVI stand for and what does it measure?
PVI stands for Positive Volume Index. It's a cumulative indicator that only updates on days when volume rises from the prior day, on the premise that price changes accompanying heavier volume may reflect broader participation rather than a small group of traders.
How is PVI different from On-Balance Volume?
OBV adds or subtracts a period's full volume based on whether the close was up or down, so every period changes the line. PVI does the opposite: it only recalculates on rising-volume days and carries forward unchanged on flat or falling-volume days, and it scales by the day's percentage price change rather than adding raw volume.
What is the traditional PVI moving average setting?
The traditional framing, associated with Paul Dysart and later Norman Fosback, compares PVI with its own long-term moving average, commonly around 255 periods, roughly a year of daily data. This is a dated convention, not a fixed rule, and should be verified against your own charting platform.
Does PVI rising always mean a bullish signal?
No. PVI rises whenever price closes higher on a rising-volume day, regardless of the broader trend or market regime. A rising PVI line describes recent price-and-volume behavior, not a forecast, and it can rise or fall for stretches that have nothing to do with the traditional PVI/MA heuristic.
Is the PVI/MA heuristic still considered reliable today?
It's a dated, debated heuristic rather than a proven predictive rule. It originated with mid-20th-century market observations and has not been established as a reliable forecasting tool under modern market structure, so it should be treated as historical context, not a trading system on its own.
Can PVI be used with cryptocurrency?
The calculation can be applied to any instrument with daily volume and closing-price data, but continuous 24/7 trading, fragmented liquidity across venues, and inconsistent volume reporting between exchanges can change what a given reading means. Validate the data source before relying on it.
How are this index and its negative counterpart intended to be used together?
The pair partitions sessions into higher-volume and lower-volume days, with each index tracking price change on one subset. The original framing treats the positive version as following crowd activity and the negative version as following quieter, potentially better-informed activity. Reading them together is the intended use; reading one alone discards the comparison that the partition exists to create.
What does it mean when both indices move in the same direction?
Agreement means price moved consistently on both higher-volume and lower-volume sessions, which is a straightforward description of a broad trend. The framing that motivates the pair only produces a distinct reading when they diverge, since divergence is what the crowd-versus-informed hypothesis predicts. Agreement is therefore less interesting than the construction implies.
Does the underlying premise still apply in modern markets?
The premise dates from a period when institutional and retail activity were more separable by volume, before electronic execution, order splitting, and continuous algorithmic participation. Whether high-volume sessions still correspond to less informed activity is doubtful and has not been demonstrated in current conditions. The indicator remains widely available, which is a different matter from remaining well founded.
References
- CMT Association: Technical Analysis Body of Knowledge and Research
- CFA Institute Research and Policy Center: Investment Research
- TA-Lib: Technical Analysis Function Library Documentation
- Positive Volume Index is associated with market analyst Paul Dysart's mid-20th-century work and was later popularized by Norman Fosback, who framed it against its own long-term moving average.
- SEC Investor.gov: Introduction to Investing