The Relative Strength Index (RSI) is one of the most popular indicators in trading — and one of the easiest to read at a glance. It's a momentum oscillator that tells you whether a market has moved too far, too fast in one direction. Here's how to use it without falling into its classic traps.
What the RSI is
The RSI was created by J. Welles Wilder and measures the speed and change of price movements. It plots as a single line that oscillates between 0 and 100, usually in a window below the price chart.
The default setting is 14 periods — the RSI looks at the last 14 candles to judge how strong recent gains are compared to recent losses. A rising RSI means upward momentum is building; a falling RSI means momentum is fading.
The 70/30 levels
Two levels do most of the work:
- Above 70 — overbought. Price has risen quickly and may be stretched; a pause or pullback becomes more likely.
- Below 30 — oversold. Price has fallen quickly and may be due for a bounce.
The 50 line in the middle acts as a rough divider: RSI above 50 leans bullish, below 50 leans bearish.
Warning
"Overbought" does not mean "sell now", and "oversold" does not mean "buy now". In a strong trend, RSI can stay overbought or oversold for a long time while price keeps going. These are alerts, not automatic signals.
The most common beginner mistake
New traders often short the moment RSI hits 70 or buy the moment it hits 30 — and get run over. In a powerful uptrend, RSI can sit above 70 for weeks. Selling into that just because the RSI is "high" fights the trend.
The fix: use the RSI with the trend, not against it. In an uptrend, treat oversold dips as potential buying opportunities in line with the trend, rather than shorting every overbought reading.
RSI divergence
One of the RSI's most useful signals is divergence — when price and RSI disagree:
- Bearish divergence — price makes a higher high but RSI makes a lower high. Momentum is weakening even as price rises — a possible reversal down.
- Bullish divergence — price makes a lower low but RSI makes a higher low. Selling is losing steam — a possible reversal up.
Divergence hints that a trend is running out of energy, though — like everything else — it needs confirmation.
Risk
The RSI is a tool, not a crystal ball. It gives false signals, especially in strong trends. Never trade an RSI level on its own — combine it with trend and price context, and always use a stop loss.
Using RSI well
A few practical habits:
- Read the trend first, then use RSI to time entries within it.
- Don't fight strong trends just because RSI is extreme.
- Watch for divergence as an early warning that momentum is shifting.
- Combine it — RSI pairs naturally with moving averages, which define the trend it should respect.
How to practise
- Add the RSI (default 14) to a daily chart of a major pair.
- Mark where it crosses 70 and 30 — and notice how often price kept going anyway.
- Look for divergences at trend tops and bottoms.
- Test it all on a demo account so there's no money at risk while you learn.
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The bottom line
The RSI is a 0–100 momentum oscillator, default 14 periods, with 70 marking overbought and 30 oversold. Those levels are alerts, not buy/sell buttons — in strong trends the RSI can stay extreme for a long time. Use it with the trend, watch for divergence, combine it with other tools, and always trade with a stop.
Educational content only, not financial advice. Trading forex carries a high level of risk. Read our full affiliate disclosure.