RSI Indicator: How to Use the Relative Strength Index

The Relative Strength Index (RSI) is a momentum oscillator, developed by J. Welles Wilder, that measures the speed and size of recent price changes on a scale of 0 to 100. Readings above 70 are conventionally called overbought and below 30 oversold, but in strong trends RSI can stay at those extremes for weeks.

This article is educational only and not financial advice. Indicators fail, past performance does not guarantee future results, and you should manage risk and do your own research.

Key takeaways

• RSI compares the average gains to the average losses over a lookback period, 14 by default, and scales the result from 0 to 100.
• Overbought (above 70) and oversold (below 30) are not sell and buy signals; in a strong trend, RSI can stay above 70 for a long time.
• In uptrends RSI tends to bounce between about 40 and 80, and in downtrends between about 20 and 60, so the range itself reveals the trend.
• RSI divergence, where price makes a new extreme but RSI does not, is a warning of fading momentum and needs price confirmation.
• Use RSI alongside trend, support and resistance and volume, not alone.

What does RSI measure?

RSI measures how strong recent up-moves are relative to recent down-moves. The formula is RSI = 100 - 100 / (1 + RS), where RS is the average gain divided by the average loss over the lookback period, 14 bars by default, using Wilder's smoothing.

If the average gain equals the average loss, RS is 1 and RSI is 50. If gains dominate, RSI rises toward 100; if losses dominate, it falls toward 0.

Example (hypothetical): over 14 days, the average up-day is +$0.90 and the average down-day is -$0.45. RS = 2.0 and RSI = 100 - 100 / 3 = 66.7. The market has been moving up twice as hard as down, but is not yet above 70.

What do the 70 and 30 levels mean?

The 70 and 30 lines mark where momentum is unusually strong or weak compared with the recent past. They flag stretched conditions, not turning points. An RSI above 70 says buyers have dominated the last 14 sessions; it does not say price must fall.

Wilder chose the levels as practical thresholds, and they are not special. Some traders use 80/20 for volatile stocks or in strong trends and 60/40 for slower ones.

Is overbought a sell signal?

No. Overbought is not a sell signal, and treating it as one is the most common RSI error. In a strong uptrend, RSI can sit above 70 for weeks while price keeps climbing, and early sells give up most of the move. Breakouts, in particular, often show RSI above 70 because the surge is the breakout.

Hypothetically, a stock rises from $40 to $62 over two months. RSI reaches 78 within the first two weeks and stays above 70 for most of the trend. Selling at 70 exits near $45. The better use is to see that momentum is strong and to look for exhaustion signs (a divergence, a failed breakout, a blow-off volume spike) before reducing.

The same applies to oversold: stocks in downtrends routinely stay below 30. Buying only because RSI is below 30 is catching a falling knife unless price also shows support and a reversal.

How do you use RSI with the trend?

Use RSI to confirm the trend and time entries within it, not to fight it. RSI behaves differently depending on the trend:

Worked example (hypothetical). A stock is in an uptrend above its rising 50-day average. It pulls back from $75 to $70.50 on lighter volume, and RSI drops from 68 to 44 and curls upward as price holds the 50-day line at $70. You buy at $71.20 above the day's high. Stop at $68.90, below the pullback low, risks $2.30. Target the prior high at $75.00, $3.80 away, about 1.65:1. If price closes below $68.90 or RSI breaks below 40 with price, the pullback thesis is wrong. Read more about the average itself in the 50-day moving average pullback strategy.

What is RSI divergence?

RSI divergence occurs when price makes a new high or low but RSI does not. It points to fading momentum, not a guaranteed reversal.

• Bearish divergence: price makes a higher high, RSI makes a lower high. Covered in bearish divergence with RSI and MACD.
• Bullish divergence: price makes a lower low, RSI makes a higher low. Covered in bullish divergence with RSI and MACD.

Divergences work best at known support or resistance and when confirmed by price, such as a broken trendline or a reversal candle. They can persist for weeks while price keeps trending, so do not trade them as an immediate signal.

What are the best RSI settings?

The 14-period setting is the standard, and no setting is best for all stocks or timeframes. A shorter period (such as 7) reacts faster and hits extremes more often; a longer one (21 or 25) is smoother.

• RSI(14): the default for daily swing trading.
• RSI(7-9): faster, more signals, more noise.
• RSI(2): the very short-term mean-reversion version, covered in the 2-period RSI strategy.
• RSI(21+): smoother for position trades.

Pick a setting and keep it, rather than optimizing to fit past data.

What are the pitfalls of RSI in strong trends?

In strong trends, RSI gives early and repeated false reversal signals. Be cautious with these:

• Shorting because RSI is above 70 in a stock making higher highs on rising volume.
• Buying a stock in a clear downtrend because RSI is below 30.
• Using RSI in thin or gap-prone stocks, where single large bars distort the calculation.
• Relying on RSI alone with no stop.

A useful alternative is to watch for RSI failing to reach its prior peak while price tests support or resistance.

How does RSI work with price structure?

RSI is most useful once you know what the chart is doing. Work in this order.

1. Identify the structure. Is the stock trending up, down or ranging? Use trendlines, moving averages, and higher highs and lows.
2. Read RSI in that context. In an uptrend, treat dips toward 40-50 as potential buy zones. In a range, 30 and 70 act as rough edges.
3. Use divergence at pattern completion points. If a stock forms a double top or head and shoulders, bearish RSI divergence on the second peak adds weight to the pattern.
4. Anchor to a level. An RSI turn that coincides with horizontal support is more meaningful than one floating in space.

See support and resistance for how to mark those levels, and the Williams %R guide for a similar oscillator with a different scale.

How does RSI fit into a full trading system?

RSI should answer one question in your system: is momentum with me or against me? A simple rule set might require (1) price above a rising 50-day average, (2) a pullback that drops RSI(14) to 40-50, (3) a bullish reversal candle, and (4) a stop below the pullback low with at least 2:1 to the prior high. Remove RSI and the trade still has structure; keep it and you have a momentum filter that avoids chasing. A system with RSI as the only rule has no stop logic and no trend filter, which is why it fails.

Common mistakes

• Treating 70 and 30 as automatic sell and buy lines.
• Ignoring the trend.
• Changing settings after each loss.
• Trading divergence without confirmation.
• Not setting a stop. See where to place a stop loss.

What should you remember when applying RSI?

Write your rules before the trade: which RSI period, which zone counts as a pullback (for example 40-50 in an uptrend), what confirms the turn, and where the stop goes. Then journal results; see how to keep a trading journal.

The bottom line

RSI is a measure of momentum, not a timing oracle. Use the 40-80 and 20-60 ranges to read the trend, buy pullbacks in uptrends when RSI resets and turns up, treat divergences as warnings that need confirmation, and keep stops defined.

StockSetups scans roughly 12,300 US stocks and ETFs each evening, and paid plans show RSI, MACD, ADX and ATR on the chart alongside detected setups and trade plans. RSI is one input among many, so combine it with price structure and sound risk management.