The best timeframe for MFI is the 14-period default on a daily chart for swing trading. Backtests show the 14 setting on a daily chart produced a 96 percent gain over 26 years versus the S&P 500, while using MFI on a 1-minute chart also produced a 43% success rate.
Most traders use a 14-period Money Flow Index, with daily charts for swing trading and 15-minute or hourly charts for intraday trades.
Shorter periods sharpen sensitivity but invite more false signals.