Key Takeaways
- RSI (Relative Strength Index) measures how fast and how far price has moved recently, on a scale from 0 to 100.
- Readings above 70 are typically read as "overbought"; readings below 30 are typically read as "oversold."
- RSI divergence, where price makes a new high or low but RSI does not, is considered a stronger signal than the overbought/oversold level alone.
- In a strong trend, RSI can stay overbought or oversold for a long time without price reversing, so RSI should never be used as a standalone signal.
- You can add RSI to any chart and test it on real historical data in our free backtesting tool.
What Is RSI?
The Relative Strength Index (RSI), developed by J. Welles Wilder and introduced in 1978, is a momentum oscillator that measures the speed and magnitude of recent price changes on a scale from 0 to 100. It is calculated by comparing the average size of recent up-moves to the average size of recent down-moves, typically over a 14-period lookback, which is why you'll usually see it labeled "RSI 14" on a chart, including in our own backtesting tool.
In plain terms: RSI answers the question "how extended is this move, relative to this market's own recent behavior?" rather than looking at the raw price level itself.
Reading Overbought and Oversold Levels
RSI is almost always shown as a line oscillating in its own sub-window beneath the main price chart, with horizontal reference lines at 70 and 30:
- RSI above 70: conventionally read as "overbought," meaning the recent advance has been unusually fast relative to this market's normal behavior, and may be due for a pause or pullback.
- RSI below 30: conventionally read as "oversold," meaning the recent decline has been unusually fast, and may be due for a bounce.
- RSI between 30 and 70: considered neutral territory, with 50 often watched as a rough dividing line between bullish and bearish momentum.
The common beginner mistake is treating "overbought" as synonymous with "sell now." In a strong, sustained trend, RSI can sit above 70 for an extended stretch while price keeps climbing. Overbought means a move has been fast, not that it is guaranteed to reverse.
RSI Divergence: A Stronger Signal
Divergence occurs when price and RSI disagree with each other, and it is generally considered a more reliable signal than a simple overbought or oversold reading on its own.
- Bearish divergence: price makes a new, higher high, but RSI makes a lower high than its previous peak. This shows that even though price pushed higher, the underlying momentum behind that push was actually weaker than the prior move, a warning sign that the uptrend may be losing strength.
- Bullish divergence: price makes a new, lower low, but RSI makes a higher low than its previous trough. This shows the selling pressure behind the new low was weaker than the prior decline, a warning sign that the downtrend may be running out of steam.
Divergence does not pinpoint an exact reversal moment. It flags that momentum is shifting beneath the surface, which is most useful when combined with a price action signal, such as a candlestick reversal pattern (see our guide on reading candlestick charts) or a test of a known support or resistance level.
Common RSI Mistakes
- Trading every overbought/oversold touch: in a trending market this produces a string of losing trades against the trend. Check the broader trend direction first.
- Ignoring the broader trend entirely: RSI works best as a timing tool within a trend you've already identified some other way, not as a standalone trend-prediction tool.
- Using RSI alone with no confirmation: as covered in our technical analysis overview, the strongest setups combine RSI with a second, independent signal rather than acting on RSI in isolation.
Practice Trading RSI on Real Historical Data
You can add RSI 14 directly onto any chart in our free backtesting and market replay tool, across 17 markets and 7 timeframes, and step bar by bar through real historical price action to see exactly how RSI behaved before and after past moves, with no real money at risk and no signup required to watch.
Frequently Asked Questions
What is a good RSI setting for beginners?
The default 14-period setting, as originally designed by Wilder, remains the standard and is what most charting platforms, including our backtesting tool, use by default. Shorter periods (such as 7 or 9) make RSI more sensitive and prone to false signals; longer periods smooth it out but react more slowly.
Is RSI better than the Stochastic Oscillator?
Neither is objectively "better"; they measure momentum in slightly different ways and often agree with each other in practice. Some traders use both together specifically because their occasional disagreements can be informative. Our dedicated Stochastic Oscillator guide covers the differences in full.
Can RSI predict exact market tops and bottoms?
No indicator can reliably predict exact tops and bottoms. RSI identifies when a move has become statistically fast or extended relative to recent history, which improves the odds around a decision, but markets can and do stay "overbought" or "oversold" for extended periods during strong trends.
What does it mean when RSI crosses 50?
Some traders use a cross above 50 as a simple sign that bullish momentum has the upper hand, and a cross below 50 as bearish momentum taking over, independent of the 70/30 overbought and oversold levels. It's a softer, earlier signal than waiting for a 70 or 30 extreme.