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Money flow index

A bounded price-volume oscillator comparing positive with total signed money flow over a chosen lookback period.

Version
v1 · 2026-09-28 · History
Domain-specific #
10791
Domain group
Social Sciences
Origin domain
Economics & Finance
Subdomain
Technical Analysis → Economics & Finance

Core Idea

The money flow index (MFI) is a bounded technical-analysis oscillator that combines price direction with trading volume. For each period it computes typical price (high + low + close)/3, multiplies by volume, and labels that raw flow positive or negative according to the change in typical price from the previous period.

Across an N-period window, positive and negative flows are totaled. The index can be written as 100 × positive flow / (positive flow + negative flow), with equivalent money-ratio form. This makes 0 mean all classified flow was negative and 100 mean all was positive, subject to edge-case conventions.

Conventional 20/80 readings and divergences are trading heuristics, not laws. The frozen source's cited comparative study found performance sensitive to stock and parameter selection. MFI measures the balance of price-volume flow within its window; it does not measure literal cash entering a security or guarantee a reversal.

Structural Signature

Sig role-phrases:

  • lookback window. Fixes N ordered trading periods. Constitutive frame. If altered: Changing N changes every accumulated flow and the oscillator.
  • typical price. Averages high, low, and close for each period. Constitutive price input. If altered: Using close alone defines a different indicator.
  • raw money flow. Multiplies typical price by volume as a dollar-flow approximation. Constitutive weighted magnitude. If altered: Without volume the calculation collapses toward a price-only oscillator.
  • direction partition. Assigns flow positive, negative, or discarded when typical price is unchanged. Constitutive classification. If altered: Sign must follow price direction rather than trade initiation.
  • bounded ratio. Maps positive flow over total signed magnitudes to 0–100. Output transformation. If altered: Threshold language is meaningless if denominator handling is undefined.
  • interpretive rule. Uses levels or divergence as heuristics rather than guaranteed forecasts. Boundary. If altered: An oscillator signal alone does not establish future reversal.

What It Is Not

  • Not literal capital inflow. Price times exchange volume is an approximation, not a trace of net external cash.
  • Not RSI. RSI weights price movement; MFI weights typical price by volume.
  • Not a forecast guarantee. Overbought, oversold, and divergence labels remain heuristics.
  • Not parameter-free. Lookback choice and edge-case rules materially affect output.

Scope of Application

MFI applies to ordered market price-and-volume series when the instrument, session, lookback, and calculation convention are explicit.

  • Equity charts. Summarizes recent directional price-volume balance.
  • Parameter studies. Compares lookback and threshold behavior across securities.
  • Divergence analysis. Contrasts price highs or lows with oscillator behavior.
  • Screening. Filters candidates under a declared trading rule.
  • Backtesting. Tests a complete rule without treating in-sample fit as proof.

Clarity

The formula reveals what the index actually normalizes: positive approximate dollar flow divided by total absolute classified flow. That clarification blocks the common inference that MFI observes net money entering or leaving the market.

Manages Complexity

A window of highs, lows, closes, volumes, and directional changes becomes one bounded statistic. The compression enables comparison but discards intraday order flow and path detail, so identical MFI values can arise from different sequences.

Abstract Reasoning

  1. Choose N, instrument, session definition, and missing-data rule.
  2. Compute typical price and raw price-volume flow for each period.
  3. Partition flows by change in typical price and aggregate each sign.
  4. Transform the two totals into the bounded oscillator with explicit zero-denominator handling.
  5. Evaluate any trading interpretation out of sample and separately from the measurement itself.

Knowledge Transfer

The formula transfers literally to price-volume time series with comparable sampling. Its trading thresholds do not transfer automatically across securities or regimes; the broader normalized-balance pattern belongs to Measurement, while the MFI inputs and direction rule remain domain-specific.

Examples

Canonical

Over a 14-day window, a chart computes typical price daily, multiplies by volume, assigns each flow by the sign of the typical-price change, and reports positive flow as a share of total classified flow on the 0–100 scale.

Mapped back: lookback window → 14 ordered days; typical price → daily HLC average; raw money flow → average times volume; direction partition → sign of daily typical-price change; bounded ratio → positive over total flow; interpretive rule → reported as balance, not forecast.

Applied / In Practice

Marek and Čadková tested different MFI settings across companies and times and found commonly recommended parameters did not supply a general advantage, illustrating that the same calculation needs instrument-specific validation.

Mapped back: lookback window → settings varied; typical price → standard MFI input; raw money flow → price-volume series; direction partition → standard rule; bounded ratio → MFI output; interpretive rule → performance tested rather than assumed.

Structural Tensions

T1: bounded comparability vs. path loss. The 0–100 scale aids comparison while hiding the order and scale of underlying flows. Diagnostic: Does the decision need the trajectory as well as the endpoint?

T2: standard thresholds vs. instrument variation. Fixed cutoffs simplify use but may not survive different volatility and volume regimes. Diagnostic: Was this parameter set validated out of sample for this instrument?

Structural–Framed Character

MFI is strongly structural as an instrument: its formula is exact, while lookback, sampling, thresholds, and trading meaning are analyst frames. Its character: a bounded price-volume measurement whose interpretation is weaker than its arithmetic.

Structural Core vs. Domain Accent

Skeletal core. Partition weighted observations by direction and report one side's share of their total magnitude.

Domain-bound accent. High/low/close prices, exchange volume, trading windows, and oscillator heuristics determine MFI.

Why not prime. Normalized signed balance travels, but this particular price-volume construction is a financial indicator.

This entry is a kind of Measurement.

  • Parent — Measurement. A defined procedure maps market observations onto a bounded scale.
  • Related — RSI. It shares oscillator form but not the volume-weighted measurand.

Relationships to Other Abstractions

Local relationship map for Money flow indexParents appear above the current abstraction, mutual partners to the right, and children below. Node labels state whether each abstraction is prime or domain-specific; colors identify relation types.Money flow indexDOMAINPrime abstraction: Measurement — is a kind ofMeasurementPRIME

Current abstraction Money flow index Domain-specific

Parents (1) — more general patterns this builds on

  • Money flow index is a kind of Measurement Prime

    Money flow index is a strict kind of Measurement: The money flow index (MFI) is an oscillator that ranges from 0 to 100.

Hierarchy path (1) — routes to 1 parentless root

Neighborhood in Abstraction Space

Money flow index sits in a moderately populated region (52nd percentile for distinctiveness): it has near-neighbors but no dense thicket of look-alikes.

Family — Financial & Economic Ratios (22 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-08

Not to Be Confused With

  • Relative strength index. Tell: Is magnitude based on price changes or typical-price volume?
  • On-balance volume. Tell: Is the result cumulative volume or a bounded window ratio?
  • Net fund flow. Tell: Are actual subscriptions/redemptions observed, or only exchange price and volume?
  • Trading signal. Tell: Is the oscillator being measured or a separate decision rule being evaluated?

References

  • Frozen Wikipedia discovery revision: https://en.wikipedia.org/wiki/Money_flow_index (revision 1342032223).
  • Preserved source candidate: https://www.researchgate.net/publication/339029303

The frozen Wikipedia revision is discovery provenance. The retained source set was reviewed for identity, formal or operational relation, and scope. The encyclopedia's structural synthesis is bounded to those claims; a thin authority surface is recorded as a nonblocking source-strengthening repair rather than concealed.