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Market Facilitation Index (MARKETFI)

Summary

Bill Williams' Market Facilitation Index (Trading Chaos, 1995): the price range a bar travelled per unit of volume traded — how much movement the market "facilitated" per tick. A rising index on rising volume is read as a move the market is absorbing; a rising index on falling volume as one it is not.

Retail material commonly abbreviates this "MFI" or "BW MFI". TA-Lib already ships TA_MFI for the Money Flow Index, so this carries the MARKETFI name used by Tulip and pandas-ta-classic.

Charting packages often overlay a four-state colour code (green / fade / fake / squat) derived from the signs of the bar-to-bar change in this index and in volume. That is an interpretive layer on top of the series, not part of it; outReal is the scalar only.

Formula

MARKETFI_t = (high_t - low_t) / volume_t

A bar with zero volume reports 0 rather than dividing: it facilitated no movement, and a successful call never emits NaN or ±Inf.

Inputs

  • inHigh — High price of each bar
  • inLow — Low price of each bar
  • inVolume — Volume of each bar

Outputs

  • outReal — Range travelled per unit of volume, per bar

Properties

Numerical Stability: Start-Independent

☐ Overlap Input
✅ Independent Y-Axis i
☐ Candlestick
☐ Can Output NaN or ±Inf
☐ Identity at Period 1

Implementation

TA-Lib Definition: marketfi.c · marketfi.yaml

NativeFile
Cta_MARKETFI.c
Rustmarketfi.rs
JavaCore_MARKETFI.java
C#Core_MARKETFI.cs

TA-Lib is also available for Python, R and more using a wrapper.

See Also

AD · ADOSC · NVI · OBV · PVI

References

  • Bill Williams, Trading Chaos, 1995, introduces the Market Facilitation Index as the price range a bar travelled per unit of volume.
  • Tulip Indicators ti_marketfi and pandas-ta-classic marketfi compute the same form, but divide unconditionally: both emit ±Inf on a zero-volume bar where this returns 0.
  • The four-state green/fade/fake/squat colour code charting packages overlay is derived from the signs of the bar-to-bar change in this index and in volume. It is an interpretive layer, not part of the series; outReal is the scalar only.
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