Money Flow Index (MFI)

August 24, 2024 Trading

Money Flow Index explained: its price-and-volume formula, a simple calculation example, common interpretations, and important limitations.

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The Money Flow Index (MFI) is a bounded technical oscillator that compares positive and negative price-times-volume values over a chosen lookback period. It ranges from 0 to 100 and is often described as a volume-weighted counterpart to the Relative Strength Index (RSI).

MFI does not trace actual cash entering or leaving a security. Its “money flow” is a formula based on typical price and reported volume.

Key Takeaways

MFI uses high, low, close, and volume data.
A common lookback is 14 periods, but a reading is meaningful only with its timeframe and settings.
High or low readings describe recent price-volume behavior; they do not guarantee a reversal.
MFI can be misleading when volume data is incomplete, inconsistent, or not comparable across venues.
A trading rule should specify confirmation, execution, position sizing, and loss limits rather than rely on an oscillator threshold alone.

How MFI Is Calculated

First calculate the typical price for each period:

TP_t = \frac{High_t + Low_t + Close_t}{3}

Then calculate raw money flow:

RMF_t = TP_t \times Volume_t

A period’s raw money flow is classified as positive when its typical price is above the previous period’s typical price and negative when it is below. Over the selected lookback:

Money\ Flow\ Ratio = \frac{\sum Positive\ RMF}{\sum Negative\ RMF}

Finally:

MFI = 100 - \frac{100}{1 + Money\ Flow\ Ratio}

Platform handling of unchanged typical prices, zero negative flow, adjusted prices, and session volume can differ. Those details should be checked before comparing results.

Simple Example

Suppose the positive raw money flow over a 14-period window totals $1.8 million and negative raw money flow totals $0.6 million.

Money\ Flow\ Ratio = \frac{1.8}{0.6} = 3

MFI = 100 - \frac{100}{1 + 3} = 75

An MFI of 75 means positive price-times-volume flow dominated the selected window. It does not mean 75% of market participants are buyers, that $1.8 million entered the security, or that price is certain to fall.

How Traders Interpret MFI

Observation	Possible interpretation	Main caution
MFI rising	Positive price-volume periods are becoming more dominant	Price may already have moved substantially
MFI falling	Negative price-volume periods are becoming more dominant	A decline in the indicator need not imply a price decline
MFI above `80`	Commonly labeled overbought	Strong trends can remain at high readings
MFI below `20`	Commonly labeled oversold	Weak markets can remain at low readings
Price and MFI diverge	Price and price-volume momentum are not confirming each other	Divergence can persist or fail

The 80 and 20 levels are conventions, not economic laws. Some platforms or strategies use different thresholds.

MFI Versus RSI

Feature	MFI	RSI
Inputs	High, low, close, and volume	Price gains and losses
Range	`0` to `100`	`0` to `100`
Main comparison	Positive versus negative price-times-volume flow	Average gains versus average losses
Volume sensitivity	Yes	No
Main data concern	Quality and meaning of volume	Price adjustments and smoothing settings

Neither indicator measures intrinsic value. Using both may add less independent confirmation than it appears because both remain heavily dependent on the same price history.

How to Evaluate an MFI Signal

Confirm the data source, session, volume definition, timeframe, and lookback.
Check whether the market has consolidated volume or fragmented reporting.
Compare the reading with price trend, support and resistance, and recent event risk.
State what confirms or invalidates the setup before placing an order.
Evaluate historical performance after fees, spreads, slippage, and realistic execution constraints.

Risks and Limitations

Volume quality: Exchange volume, consolidated volume, futures contract volume, and tick volume are not interchangeable.
False extremes: High MFI can accompany a continuing rally, and low MFI can accompany a continuing decline.
Lag: The lookback window incorporates past observations and may react after price changes.
Volume spikes: Rebalancing, block trades, contract rolls, or one-time events can distort the calculation.
Divergence ambiguity: A divergence is an observation, not a timing signal.
Data adjustments: Corporate actions or different adjusted-price conventions can change historical readings.

The CFTC Futures Glossary provides public definitions for volume, momentum, and technical analysis. Its trading-system advisory also explains why claims about mechanical trading results require scrutiny. These sources do not endorse MFI or any threshold.

FAQs

Does an MFI reading above 80 mean sell?

No. It is commonly labeled overbought, but a strong trend can keep MFI elevated. A threshold alone does not define an entry, exit, position size, or acceptable loss.

Is Money Flow Index actual capital flow?

No. MFI uses typical price multiplied by volume. It is not a record of investor deposits, withdrawals, or net cash entering a security.

Can MFI be used when reliable volume is unavailable?

The formula can be calculated only from the available volume measure, but the result may not be comparable with exchange-volume MFI. The data source and its limitations should be disclosed.

Momentum: The direction and speed of price change over a selected interval.
Divergence: A disagreement between price and an indicator.
Relative Strength Index: A bounded price-only momentum oscillator.
Technical Indicators: Formula-based transformations of market data.

This article is educational and does not provide personalized investment or trading advice. MFI cannot guarantee a return or prevent a loss.

Momentum

Relative Strength