The Money Flow Index (MFI), developed by Gene Quong and Avrum Soudack, uses both price and volume to measure buying and selling pressure. The MFI value ranges from 0 to 100. A MFI value above 80 indicates a possible overbought situation and a value below 20 indicates a possible oversold condition.
The formula is essentially a volume-weighted relative strength index (RSI). However, instead of using simple close prices, MFI uses the typical price multiplied by volume. The result is then used in the RSI calculation as a ratio of average volume weighted size of the up-closes over the past “n” periods and compared to the average volume weighted size of the down-closes. The result is indexed between 0 and 100.
\[Pivot = \frac{(High + Low + Close)}{3}\]
\[MF = Money\;Flow = \begin{pmatrix} if\;Pivot_{t} > Pivot_{t-1}, & Pivot \times Volume \\ if\;Pivot_{t} < Pivot_{t-1}, & -Pivot \times Volume & \end{pmatrix} \]
\[MR = Money\;Ratio = \frac{\sum_{1}^{n} Positive\;MF}{\sum_{1}^{n} Negative\;MF}\]
over a user defined n-periods
\[MFI = 100 - \frac{100}{1+ MR_{n-periods}} \]