The Relative Strength Index, or RSI, is a momentum indicator that moves between 0 and 100. It compares the size of recent gains with recent losses to show whether price momentum is running hot or cooling off.
Traders use RSI to gauge trend strength, to spot conditions often called overbought or oversold, and to look for early signs that a move is tiring.
How RSI is calculated
RSI starts with a lookback window, commonly 14 periods. A period can be a day, an hour or any bar on your chart. Within that window, the indicator separates up closes from down closes and builds smoothed averages of each.
- Average Gain: the smoothed mean of positive closes over the window.
- Average Loss: the smoothed mean of absolute negative closes over the window.
Divide Average Gain by Average Loss to get RS. Turn that into an index with the formula: RSI = 100 − 100 ÷ (1 + RS). The result is bounded, so you always see a value between 0 and 100.
Small example. Suppose over 14 days, the average up day is 1.2 and the average down day is 0.8. RS is 1.2 ÷ 0.8 = 1.5. Plugging in gives RSI = 100 − 100 ÷ 2.5 = 60. An RSI near 60 says upside momentum has been stronger than downside over the chosen window.
Most charting platforms use J. Welles Wilder’s smoothing, which behaves like an exponential average. You can usually change the length. Shorter lengths react faster but whipsaw more, while longer lengths are steadier and laggier.
Overbought, oversold and trend ranges
The common guideposts are 70 and 30. Above 70 is often labelled overbought, below 30 oversold. Those words do not mean price must snap back immediately. They describe stretched momentum relative to the recent past.
RSI also behaves differently in trends versus ranges:
- In uptrends, RSI often spends time between 40 and 80. Pullbacks that hold 40 to 50 can mark trend support.
- In downtrends, RSI often lives between 20 and 60. Bounces that stall near 50 to 60 can mark trend resistance.
Some traders tighten the bands to 80 and 20 for very volatile markets, or relax them to 60 and 40 when conditions are quiet. The point is to calibrate levels to the asset’s behaviour and timeframe.
When price is ranging between support and a resistance level, RSI tends to swing cleanly between lower and upper bands. In such conditions, fading overbought or oversold can work better than chasing breakouts.
Divergences and failure swings
A divergence happens when price makes a new extreme but RSI does not. It hints that momentum is not confirming the move.
- Bearish divergence: price makes a higher high, RSI makes a lower high. It can foreshadow a slowing uptrend or a turn.
- Bullish divergence: price makes a lower low, RSI makes a higher low. It can warn that sellers are tiring.
Divergences are not timing tools on their own. Many appear before any real turn, and some resolve with price simply pausing before continuing.
Failure swings are patterns within RSI itself. A classic bearish failure swing is RSI pushing above 70, pulling back, then failing to make a higher high on its next push before breaking the prior RSI low. The mirror image applies for a bullish failure swing near 30. These patterns aim to catch momentum shifts without waiting for price to set a new extreme.
Settings, timeframes and variations
Default settings are 14 periods on daily charts, but there is no single right choice. Consider:
- Intraday trading: many use 7 to 14 periods to get more responsive signals, accepting more noise.
- Swing or position trading: longer windows such as 21 or 28 can smooth out whipsaws and emphasise bigger swings.
- Markets with heavy volatility, including crypto: thresholds may be pushed wider, for example using 80 and 20, to avoid constant false alerts.
There are variants such as RSI with moving average crossovers, or RSI calculated on different price inputs. Platform behaviour can vary, so check how your charts define gains and losses, how they smooth them, and whether they allow cut-off or cumulative methods when the indicator first starts.
Practical uses and common traps
RSI can support a plan in several ways:
- Trend confirmation: in a rising market, pullbacks that hold RSI above 40 to 50 can help time add-ons. In a falling market, rallies that fail near 50 to 60 can frame short ideas.
- Entries in ranges: in sideways conditions, some traders buy on dips toward 30 and sell near 70, with stops beyond the range.
- Breakout filter: strong breakouts often come with RSI pushing into high territory and staying there. A quick failure back below prior RSI levels can warn of a false break.
- Confluence: pairing RSI with price structure, volume or another indicator can reduce false signals. For example, combine it with a pullback to a prior level, or with volume tools like on-balance volume.
Watch for these pitfalls:
- Treating overbought as a sell signal: in strong trends, RSI can stay elevated for long stretches while price grinds higher. The same applies to oversold in downtrends.
- Ignoring timeframe context: an oversold reading on a 5 minute chart can sit inside a strong daily uptrend. Signals often conflict across timeframes.
- Forcing divergence trades: many divergences fail. Waiting for price confirmation, such as a break of a swing low or high, can help.
- Confusing RSI with relative strength versus a benchmark: RSI measures internal momentum of one instrument. It does not compare an asset to an index or peer group.
As with any indicator, RSI is a lens, not a complete system. It works best when it complements clear rules on entries, exits and risk management, and when its settings match the market and timeframe you trade.