What Is the RSI Indicator? Relative Strength Index Explained

The Relative Strength Index (RSI) is a momentum indicator that measures the speed and magnitude of recent price changes on a scale from 0 to 100. It tells you whether a stock is potentially overbought or oversold, helps identify divergence, and can confirm trend strength. RSI is one of the first indicators most traders learn, and for good reason — it is simple, versatile, and effective.

How RSI Is Calculated

RSI compares the average gain to the average loss over a set period, typically 14 periods. The formula produces a value between 0 and 100.

When recent gains are large relative to recent losses, RSI is high (above 50). When recent losses dominate, RSI is low (below 50). The further from 50, the stronger the momentum in that direction.

The standard 14-period setting works for most applications. Shorter periods (like 7) make RSI more sensitive and produce more signals. Longer periods (like 21) smooth the indicator and produce fewer, more reliable signals.

Overbought and Oversold Levels

The most basic RSI interpretation uses the 70 and 30 levels. RSI above 70 is considered overbought — the stock has risen sharply and may be due for a pullback. RSI below 30 is considered oversold — the stock has dropped sharply and may bounce.

However, overbought does not mean sell, and oversold does not mean buy. In a strong uptrend, RSI can stay above 70 for extended periods as the stock continues to rally. In a strong downtrend, RSI can remain below 30 while price keeps falling.

RSI overbought and oversold readings are warnings, not signals. They tell you momentum is stretched, but they do not tell you when the reversal will happen. Always combine RSI with price action and levels.

Use overbought and oversold readings as alerts to pay attention, not as automatic triggers. When RSI hits 70, start watching for a reversal signal. When it hits 30, watch for a bounce. But let price action confirm before you act.

RSI as a Trend Filter

A simpler and often more effective use of RSI is as a trend filter using the 50 level. When RSI is above 50, upward momentum is dominant — favor long trades. When RSI is below 50, downward momentum is dominant — favor shorts.

This cuts through the noise. You do not need to wait for extreme readings. If RSI is above 50 and you have a bullish setup on the chart, the momentum supports your trade. If RSI is below 50 and you have a bearish setup, the momentum supports your trade.

This application works on any timeframe and with any strategy. It is one of the most underrated uses of RSI because traders fixate on the 70/30 extremes and ignore the middle.

RSI Divergence

Divergence between price and RSI is one of the most powerful signals in technical analysis. It warns of weakening momentum before the reversal actually happens.

Bullish divergence: Price makes a lower low, but RSI makes a higher low. The selling momentum is weakening. A bottom may be forming.

Bearish divergence: Price makes a higher high, but RSI makes a lower high. The buying momentum is fading. A top may be forming.

Divergence works best at extremes — bullish divergence near RSI 30, bearish divergence near RSI 70. Divergence in the middle of the RSI range is less significant.

RSI Failure Swings

A failure swing is a specific RSI pattern that generates a signal without looking at price at all.

Bullish failure swing: RSI falls below 30, bounces above 30, pulls back but stays above 30, then breaks above the initial bounce high. This pattern signals that buyers are taking control.

Bearish failure swing: RSI rises above 70, drops below 70, rallies back but stays below 70, then breaks below the initial drop low. Sellers are taking control.

Failure swings are pure momentum signals. They are less common than divergence but often more decisive when they appear.

Combining RSI With Price Action

RSI is most effective when combined with chart-based analysis. A bullish RSI divergence at a major support level is a high-probability signal. An overbought RSI reading at a strong resistance level with a bearish candlestick pattern is a clean short setup.

Use RSI to confirm what you see on the chart. If the chart shows a bullish setup and RSI supports it (above 50, showing divergence, or bouncing from oversold), your confidence increases. If the chart shows bullish but RSI shows bearish divergence, be cautious.

RSI Across Timeframes

Check RSI on both your trading timeframe and one timeframe higher. If both timeframes show RSI above 50, the momentum is aligned and your long trades have stronger backing. If they conflict — one bullish and one bearish — the trade is riskier.

Higher timeframe RSI readings carry more weight. Daily RSI oversold is more significant than 5-minute RSI oversold because it reflects more participants and more volume.