RSI Indicator: Relative Strength Index

What Is the RSI Indicator?

The Relative Strength Index (RSI) is a momentum oscillator that ranges from 0 to 100. Developed by J. Welles Wilder in 1978, it remains one of the most widely used technical indicators for good reason: it gives you a single number that captures the balance between buying and selling pressure over a recent period.

The name is misleading. RSI has nothing to do with comparing one stock's strength to another. "Relative" here means relative to the stock's own recent performance. Specifically, RSI measures the ratio of average gains to average losses over N periods (default: 14).

The formula is simple. For each period, track whether the close was higher or lower than the previous close. Average the gains over 14 periods, average the losses over 14 periods, then compute:

RSI = 100 − (100 / (1 + RS)), where RS = Average Gain / Average Loss.

When gains dominate, RS is large and RSI approaches 100. When losses dominate, RS is small and RSI approaches 0. When gains and losses are roughly equal, RSI sits near 50.

After the initial 14-period calculation, subsequent values use a smoothed average: the previous average is multiplied by 13, plus the current gain or loss, divided by 14. This makes RSI responsive to recent price action while smoothing out noise. The smoothing also means RSI has "memory": a stock that had a sharp selloff last week still affects today's RSI, even if price has been flat since. This lag is worth understanding because it means RSI can stay depressed (or elevated) longer than you expect after a big move.

The chart above shows AAPL with RSI(14) plotted beneath the price. Notice how RSI moves with the general trend of price but exaggerates turning points, which is what makes it useful as a momentum tool.

Overbought and Oversold Levels

The standard RSI levels are 70 (overbought) and 30 (oversold). When RSI crosses above 70, the stock is considered overbought. Below 30, oversold.

Now for the part most guides get wrong, or at least gloss over:

Overbought means buyers have been aggressive recently. In a strong uptrend, that's expected. RSI above 70 in a bull run is confirmation of strength, not a warning. The signal comes when RSI finally breaks down from overbought territory. That's when momentum is shifting.

The same applies in reverse. A stock in a downtrend can remain oversold for a long time. RSI below 30 on a stock making new lows every day is telling you sellers are firmly in control. Buying just because RSI hit 30 is catching a falling knife.

TSLA is a textbook example. During strong rallies, RSI frequently pushes above 70 and stays there. During selloffs, it can camp below 30 for weeks. The overbought/oversold levels are starting points for analysis, not standalone trading signals.

Adjusting the levels

Some traders use 80/20 instead of 70/30 for volatile stocks. Others use 60/40 in strong trends to catch momentum entries earlier. There's no single correct threshold. It depends on the asset and the timeframe.

A practical approach: observe where RSI actually reverses on the stock you're trading. If AAPL's RSI consistently bounces off 40 during uptrends rather than reaching 30, use 40 as your oversold level for that stock. The standard levels are starting points. Adjust them based on the asset's actual behavior rather than treating them as universal constants.

RSI Divergence

Divergence is where RSI becomes most useful. It occurs when price and RSI move in opposite directions, signaling that momentum is weakening even as price continues in its current direction.

Bullish divergence

Price makes a lower low, but RSI makes a higher low. This is a bullish signal. It means that even though price dropped further, the selling pressure behind the move was weaker than the previous drop. Sellers are losing conviction.

Bearish divergence

Price makes a higher high, but RSI makes a lower high. This is a bearish signal. Price pushed higher, but buying pressure was weaker. Buyers are running out of steam.

Reliability

Divergence is stronger on daily and weekly timeframes. On intraday charts (5-minute, 15-minute), divergences appear constantly and most of them resolve as nothing. The noise-to-signal ratio on short timeframes makes divergence trading unreliable.

Even on daily charts, divergence can persist for a long time before price actually reverses. A bearish divergence can form and then another higher high with another lower RSI high can form again, with multiple divergences stacking up before the move finally happens. Divergence tells you momentum is weakening, not that a reversal is imminent.

The strongest divergence signals tend to appear after extended trends. If a stock has been trending up for months and you spot the first bearish divergence, pay attention but don't act immediately. If you then see a second bearish divergence on the next rally attempt, the probability of a meaningful pullback increases substantially. Multiple consecutive divergences are more significant than a single instance.

RSI Trading Setups

Three concrete RSI-based setups that work in practice. Each one has specific entry rules, not just "RSI is low, buy."

1. Oversold bounce

This setup triggers when RSI drops below 30, then crosses back above 30. The cross back above is the key. You're not buying while RSI is below 30 (that's where the knife is still falling).

• Entry: RSI crosses back above 30 from below
• Confirmation: Price closes above the low of the oversold period
• Stop: Below the recent swing low
• Context: Works best in an overall uptrend or at major support levels. In a downtrend, skip it because you're fighting the trend

This is a bullish mean-reversion setup. The idea is that selling pressure has exhausted itself and buyers are stepping back in.

2. Overbought rejection

The mirror image: RSI rises above 70, then crosses back below 70. Again, the cross is what matters. You don't short just because RSI hit 70.

• Entry: RSI crosses back below 70 from above
• Confirmation: Price closes below the high of the overbought period
• Stop: Above the recent swing high
• Context: Best in a downtrend or at major resistance. In a strong uptrend, this setup will get you chopped up

This is a bearish setup. Buying pressure peaked and is now fading. But remember: in strong uptrends, RSI can bounce off 40-50 and go right back to overbought. Always check the larger trend.

3. Center-line crossover

RSI crossing above or below 50 acts as a trend confirmation signal. This is subtler than the overbought/oversold setups but often more reliable because it focuses on the shift in dominance between buyers and sellers rather than extremes.

• RSI crosses above 50: Bullish. Average gains are now exceeding average losses. Trend is shifting upward
• RSI crosses below 50: Bearish. Average losses exceeding gains. Trend is shifting downward
• Best use: Combine with a moving average crossover or breakout for confirmation. On its own, 50-line crosses generate too many false signals in choppy markets

The center-line crossover works well as a filter. If RSI is above 50, only take long setups. Below 50, only take shorts. This single rule eliminates a lot of counter-trend trades that look tempting but fail.

One practical variation: look for RSI to pull back to 50 during a trend and bounce. In a healthy uptrend, RSI pulling back to 50 often coincides with a price pullback to a moving average or support level. The bounce off 50 confirms buyers are still in control and the dip was just a normal retracement, not the start of a reversal.

RSI + MACD: Confirmation Signals

RSI and MACD are the two most popular momentum indicators, and they complement each other well. RSI is bounded (0-100) and excels at identifying extremes. MACD is unbounded and excels at identifying trend direction and momentum shifts.

Using them together

The most effective combination: use MACD for trend direction and RSI for entry timing.

• MACD above signal line + RSI bouncing off 40-50: Bullish entry in an uptrend. MACD confirms the trend is up, RSI confirms a pullback has ended
• MACD below signal line + RSI rejecting 60-50: Bearish entry in a downtrend. MACD confirms the trend is down, RSI confirms a bounce has failed

Double divergence

When both RSI and MACD diverge from price at the same time, the signal is significantly stronger than either alone. If price makes a higher high but both RSI and MACD make lower highs, momentum is deteriorating across multiple measurements. This is as close to a high-probability reversal signal as you'll get from indicators alone.

The chart above shows QQQ with both RSI and MACD. When you see them tell the same story, both confirming a trend or both diverging from price, the signal carries more weight than either indicator alone.

For a deeper breakdown of MACD mechanics, signal lines, and histogram patterns, see the full MACD indicator guide.

Common RSI Mistakes

After years of watching traders use RSI, the same mistakes come up over and over.

1. Treating overbought as an automatic sell signal

This is the number one RSI mistake, and it costs people real money: overbought means strong momentum, not "time to sell." In 2020-2021, NVDA spent most of its time with RSI above 60, frequently above 70. Anyone who sold every time RSI hit 70 missed a generational run.

The signal is when RSI breaks down from overbought, not when it enters overbought. And even then, it's a signal to pay attention, not to immediately press the sell button.

2. Ignoring trend context

RSI behaves differently in uptrends and downtrends. In a strong uptrend, RSI tends to oscillate between 40 and 80. The "oversold" bounce happens at 40-50, not at 30. In a strong downtrend, RSI oscillates between 20 and 60, and the "overbought" rejection happens at 50-60, not at 70.

If you're rigidly using 70/30 regardless of trend, you'll miss most of the actionable signals. The 70/30 levels work best in range-bound, sideways markets. In trending markets, shift your levels with the trend.

3. Using default settings without thinking

The 14-period default works reasonably well on daily charts. But applying it blindly to a 5-minute chart gives you wildly different behavior. On shorter timeframes, 14 periods covers just over an hour of trading, and RSI will whipsaw constantly.

Some guidelines:

• Daily charts: 14-period is the standard and works well
• Weekly charts: 14-period or even 10-period to increase sensitivity
• Intraday (5-15 min): Consider 21 or 25 periods to smooth out noise
• Swing trading (4-hour): 14 works, but test 10 for faster signals

There's no magic number. The point is to think about what 14 periods actually represents on your timeframe and whether that lookback window makes sense for the kind of moves you're trying to capture.

4. Using RSI in isolation

RSI is a single input. It tells you about momentum over a fixed lookback window. It doesn't know about support and resistance, volume, news catalysts, or market regime. The best RSI traders use it as one piece of a larger picture, confirming signals from price action, volume, and other indicators rather than trading RSI signals alone.

At minimum, check the chart before acting on any RSI signal. Is the stock at a meaningful support or resistance level? Is volume increasing or drying up? Is there an earnings report tomorrow that could make technical signals irrelevant? RSI can tell you momentum is shifting, but the context around that shift determines whether it's a tradeable setup or a trap.

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