Summary
It seems like the Relative Strength Index (RSI) has been around forever. But its origins date to only the late 1970s. The RSI is used by technical traders to identify the time to buy an asset, commodity, or index fund. It is a contrarian concept and it examines the recent trading pattern in an asset and forecasts a mean reversion. Thus, when the RSI moves too high, it signals the potential for a reversal or pullback. When it gets too low, it may be signaling a buying opportunity. The RSI on the S&P 500 has been on the high side since about mid-May, following the positive market response out of the “Liberation Day” lows of early April. On that date, the RSI was a few ticks above 21. By mid-May, the RSI on the S&P 500 had climbed back to the high-60s area. As companies showed they were navigating tariffs successfully and market optimism built, the RSI on the S&P 500 climbed to the mid-70s early in July. The index RSI ticked along in a range between the mid-60s and the mid-70s until early October. As doubt began to build regarding the sustainability of the AI trade, the market advance began to wobble — and gradually, the RSI began to work lower. By 10/10/25, the RSI on the S&P 500 was in the upper 40s. Despite a late-month rally, it worked down across November, hitting a low of 34.9 on 11/20/25
