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.