Introduction
The Money Flow Index (MFI) is a momentum indicator that is similar to the Relative Strength Index (RSI) in both interpretation and calculation. However, MFI is a more rigid indicator in that it is volume-weighted, and is therefore a good measure of the strength of money flowing in and out of a security. It compares "positive money flow" to "negative money flow" to create an indicator that can be compared to price in order to identify the strength or weakness of a trend. Like the RSI, the MFI is measured on a 0 - 100 scale and is often calculated using a 14 day period.
Formula
The "flow" of money is the product of price and volume and shows the demand for a security and a certain price. The money flow is not the same as the Money Flow Index but rather is a component of calculating it. So when calculating the money flow, we first need to find the average price for a period. Since we are often looking at a 14-day period, we will calculate the typical price for a day and use that to create a 14-day average.
Typical Price = ( (Day High + Day Low + Day Close) / 3)
Money Flow = (Typical Price) x (Volume)
The MFI compares the ratio of "positive" money flow and "negative" money flow. If typical price today is greater than yesterday, it is considered positive money. For a 14-day average, the sum of all positive money for those 14 days is the positive money flow. The MFI is based on the ratio of positive/negative money flow (Money Ratio).
Money Ratio = (Positive Money Flow / Negative Money Flow)
Finally, the MFI can be calculated using this ratio:
Money Flow Index = 100 - (100 / (1 + Money Ratio))
The fewer number of days used to calculate the MFI, the more volatile it will be.
Use
The MFI can be interpreted much like the RSI in that it can signal divergences and overbought/oversold conditions.
Divergences
Positive and negative divergences between the stock and the MFI can be used as buy and sell signals respectively, for they often indicate the imminent reversal of a trend. If the stock price is falling, but positive money flow tends to be greater than negative money flow, then there is more volume associated with daily price rises than with the price drops. This suggests a weak downtrend that threatens to reverse as money flowing into the security is "stronger" than money flowing out of it.
Overbought/Oversold
As with the RSI, the MFI can be used to determine if there is too much or too little volume associated with a security. A stock is considered "overbought" if the MFI indicator reaches 80 and above (a bearish reading). On the other end of the spectrum, a bullish reading of 20 and below suggests a stock is "oversold".
Examples
The PeopleSoft (PSFT) example shows how the MFI is a useful indicator of market tops and bottoms. Overbought conditions in September and January resulted in reversals of uptrends, and the oversold condition in March resulted in a reversal of the prior downtrend.
The Washington Mutual example shows how the MFI can also be used to anticipate imminent reversals. If prices are trending upwards and the MFI is trending downwards, reversals such as those December and March may occur. However, divergences between price and MFI can exist for long periods of time. Therefore, as with all indicators, the MFI should be used in tandem with other indicators that can provide confirmation of any signals it sends. MFI and SharpCharts2
MFI and SharpCharts
MFI is available on our SharpCharts charting tool. In the example box, MFI has been assigned 14 and 30 day periods. A swing trader might prefer 14-day periods, while an investor may prefer 30-day periods. Users are encouraged to test different MFI settings and judge for themselves which ones work best and suit their particular trading/investing style.
