The Relative Strength Index (RSI) was introduced by J. Welles Wilder in 1978 and is still one of the most-used indicators on every trading platform. It is simple to read, works on any market, and — when used correctly — adds useful information about momentum.
It is also widely misused. "RSI above 70, sell!" is the fastest way to lose money in a strong bull market. Here is how RSI really works and how to use it well.
How RSI is calculated
RSI compares the size of recent gains with the size of recent losses over a period (14 bars by default):
- Average gain and average loss are calculated over the last 14 periods (using Wilder's smoothing).
- Relative strength (RS) = average gain ÷ average loss.
- RSI = 100 − 100 ÷ (1 + RS).
The result moves between 0 and 100. Higher values mean gains have dominated recently; lower values mean losses have.
Reading RSI
- Above 70: traditionally "overbought" — prices have risen fast.
- Below 30: traditionally "oversold" — prices have fallen fast.
- Around 50: the midpoint. Many traders treat RSI above 50 as bullish momentum and below 50 as bearish.
The key word is momentum. Overbought does not mean "about to fall". In a strong uptrend, RSI can stay above 70 for weeks while price keeps climbing.
RSI in trends vs ranges
In ranges, classic overbought/oversold readings work better: buying near 30 and selling near 70 can catch swings between support and resistance.
In trends, RSI behaves differently:
- In uptrends, RSI tends to stay between roughly 40 and 80; dips toward 40–50 are often buying opportunities.
- In downtrends, RSI tends to stay between roughly 20 and 60; rallies toward 50–60 often fail.
This idea — sometimes called RSI range shift — is far more useful than blindly fading 70 and 30.
RSI divergence
A bearish divergence happens when price makes a higher high but RSI makes a lower high — momentum is weakening. A bullish divergence is the opposite at lows. Divergences are early warnings, not entry signals on their own. Wait for price confirmation, such as a break of a trendline or a reversal candle at a key level.
Best RSI settings
- 14 periods is the standard and a good default.
- Shorter (2–7) makes RSI more sensitive — used in short-term mean-reversion systems such as the well-known RSI(2) approach.
- Longer (21–25) smooths RSI for position trading.
Different settings suit different strategies. Test before you trust.
Three RSI strategies you can backtest today
1. RSI oversold bounce
Buy when RSI(14) crosses back above 30; exit when RSI reaches 70 or at a stop-loss. Open this exact setup in our RSI strategy backtest to see how it performed on real data.
2. Trend pullback with RSI
Only buy when price is above the 200 EMA (uptrend), and enter when RSI(14) crosses back above 40 after a dip. Exit at RSI 70 or if price closes below the 200 EMA. Try it in the EMA 200 pullback strategy.
3. RSI 50 momentum filter
Use RSI above 50 as a filter for any long setup — for example, only take breakouts when RSI confirms momentum.
Common RSI mistakes
- Shorting just because RSI is above 70 in a strong uptrend.
- Buying just because RSI is below 30 in a crash — oversold can get more oversold.
- Using RSI alone without looking at price structure and levels.
- Over-optimising the period and levels until the backtest looks perfect — and fails live.
RSI and risk management
Any RSI strategy needs the same discipline as every other strategy: a stop-loss where the idea is wrong, position sizing from that stop, and a realistic expectation of losing streaks. Use the position size calculator and stress-test your results with the Monte Carlo simulator.
Key takeaways
- RSI measures momentum, not value. Overbought can stay overbought.
- Use classic 70/30 levels in ranges and shifted ranges (40/80, 20/60) in trends.
- Divergences are warnings — wait for price confirmation.
- Backtest any RSI rule before using real money.
Frequently asked questions
What is the best RSI setting for intraday trading?
Many intraday traders use the default 14 on 5- or 15-minute charts; some use shorter periods for faster signals. Backtest on your market and timeframe to decide.
Is RSI a leading or lagging indicator?
RSI is calculated from past prices, so it lags price, but divergences can give early warnings of weakening momentum.
Can RSI be used for crypto and forex?
Yes. RSI works on any liquid market. Crypto often stays overbought or oversold longer because of strong trends, so trend context matters even more.
Where can I learn RSI and other indicators properly?
Our technical analysis course covers RSI, MACD, moving averages and volume with live chart practice.
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