RSI Indicator Explained: Beyond Oversold and Overbought
Every trader knows RSI: below 30 is oversold, above 70 is overbought. That's the textbook. The problem is the textbook is incomplete — and trading on it alone will get you destroyed in trending markets. Here's what RSI actually tells you.
What RSI Is
The Relative Strength Index measures the speed and magnitude of price movements on a 0-100 scale. Developed by J. Welles Wilder in 1978, it compares the magnitude of recent gains to recent losses over a specified period (typically 14 bars).
RSI = 100 - (100 / (1 + Average Gain / Average Loss))
The Standard Interpretation (And Its Trap)
Below 30 = oversold, above 70 = overbought. This is where most traders stop learning about RSI — and where they start losing money.
The trap: RSI can stay below 30 for extended periods during strong downtrends. A stock dropping 20% in a week will have RSI at 20 or lower — and it can stay there. "Oversold" doesn't mean "about to reverse." It means "selling pressure has been strong." In a strong downtrend, selling pressure should be strong.
Buying every RSI below 30 in a downtrend is catching falling knives. The RSI signal is a starting point, not a command.
RSI Divergence: The Signal Most Traders Miss
Divergence is when price and RSI disagree. This is far more reliable than simple oversold/overbought readings.
- • Bearish divergence: Price makes a higher high, but RSI makes a lower high. Momentum is weakening even as price rises. Often precedes a reversal.
- • Bullish divergence: Price makes a lower low, but RSI makes a higher low. Selling pressure is fading. Often precedes a bounce.
Divergence works because RSI captures momentum shifts before they show up in price. By the time price reverses, RSI has already told you the underlying momentum was changing.
TradeTestr's Two RSI Strategies
RSI Reversal — Pure contrarian. Goes long when RSI drops below 30 and starts rising. Short when RSI exceeds 70 and starts falling. No other filters. Works in ranging markets, gets destroyed in trends.
Bollinger Bounce + RSI — RSI confirms Bollinger Band touches. Long when price hits the lower band AND RSI is below 30. Short when price hits the upper band AND RSI is above 70. The Bollinger Band filter adds a volatility dimension that pure RSI lacks — it prevents entries when price is just riding the band in a strong trend.
When RSI Works and When It Fails
- ✓ Works: Ranging markets where price oscillates between support and resistance. RSI extremes reliably mark the edges.
- ✗ Fails: Strong trends. RSI stays extreme for days or weeks. Every "reversal signal" is a trap — you enter against the trend and get steamrolled.
Test It Yourself
Test RSI Reversal and Bollinger Bounce + RSI on the backtester — see the win rate, profit factor, and Monte Carlo survival for different instruments and timeframes. Check which RSI setups made the Strategy Lab leaderboard.