Negative Volume Index

What it measures

NVI tracks cumulative price changes only on days when volume was lower than the prior day, ignoring high-volume days entirely. The underlying theory, going back to Paul Dysart in the 1930s and popularized by Norman Fosback, is that "smart money" (informed institutional investors) tends to trade quietly on low-volume days, while the less-informed "crowd" piles in on high-volume days driven by news and emotion.

How readings are interpreted

A rising NVI suggests price is advancing on the low-volume days specifically — consistent with the theory that informed participants are steadily accumulating. NVI is traditionally compared to its own long-term moving average (often a 255-day/roughly one-year average) rather than read as a standalone level.

Conventional levels

• NVI above its own long-term (e.g. 255-day) moving average: historically associated with a bullish bias, per the original research
• NVI below its long-term moving average: less clearly bullish, per the same research
• Because NVI only updates on low-volume days, it changes more slowly and smoothly than most indicators

Where it works, and where it does not

This app computes NVI only for long-term daily analysis, not for shorter swing/hourly timeframes — the whole premise depends on distinguishing meaningful patterns across many low-volume days, which requires a long-term dataset to be statistically meaningful. Best suited to long-term position/investment decisions, not short-term trading.

Commonly read alongside

• PVI: The direct complementary pair — comparing NVI's read (quiet-day trend) against PVI's read (active-day trend) gives a fuller picture of who's driving price
• Long-term moving averages: NVI is conventionally read against its own long-run average rather than against price directly
• Fundamental conviction: Often used by longer-term, buy-and-hold-oriented investors alongside fundamental research rather than by short-term traders

Known limitations

• The underlying "smart money trades quietly" theory is dated (1930s) and its relevance to modern, largely algorithm-driven volume patterns is debated
• Changes slowly, by design, making it unsuitable for anything beyond long-term analysis
• Like OBV/PVT, the raw cumulative level isn't meaningful on its own — only the trend relative to its own long-term average matters

In practice

• Use exclusively for long-term, position-level analysis — not for short-term trading decisions
• Read NVI relative to its own long-term (roughly one-year) moving average, not as a standalone number
• Consider pairing with PVI to see whether quiet-day and active-day price trends agree or diverge
• Treat as one supporting data point in a long-term thesis, not a primary signal on its own