Should You Buy a Stock at RSI 30?

One of the first things most traders learn is that when a stock's RSI drops below 30, the stock is considered "oversold," and oversold means buy. The logic is that its price has fallen too far, too fast, and is due for a snap back.

We put that theory to the test. We backtested buying at RSI 30 on the S&P 500 and ten of the largest individual stocks and measured whether buying at RSI 30 beat buying on a random day.

On the index, oversold is a real (if small) edge

On the S&P 500, buying the RSI-30 dip returned a median 2.9% over the next month and closed higher 73% of the time, a clear edge from the 1.4% you would have made buying on a random day.

On single stocks the edge disappears

Three names rewarded the dip-buyer (TSLA, GOOGL, META). Four punished them (AAPL, NFLX, AMZN, NVDA). Pooling the eight together, buying at RSI 30 returned a median 1.5% over the next month, short of the roughly 2.4% earned by buying those same names on a random day.

And then there is NVDA. The single best-performing mega-cap of the era, the one a dip buyer would most want to own, is where buying at RSI 30 produced the worst results: a median loss of 6.2% over the next month, higher only 36% of the time. Those oversold readings were not bargains. They sat in the middle of its sharpest drawdowns, and buying the signal meant catching the falling knife over and over.

Why the index bounces and a stock often does not

On the S&P 500, an oversold reading aggregates 500 companies, and it takes broad, indiscriminate selling to drag the whole basket down. That kind of indiscriminate fear tends to overshoot and then reverse. On a single stock the same reading usually signals a real problem with that one company: an earnings miss, a guidance cut, or a broken thesis. The market is simply repricing the problem, which is why the decline is often justified and continues.