Indicators / Momentum / RSI
RSI Indicator Explained: Overbought, Oversold, the 50 Level and Divergence
Quick answer
The Relative Strength Index (RSI) measures momentum: how strong recent gains are compared with recent losses, on a scale of 0 to 100. Above 70 means strong upward momentum and below 30 strong downward momentum, not an automatic reversal. The 50 line and divergence usually tell you more than 70 and 30 on their own.
Video: RSI for Beginners. Prefer a slower, podcast-style version? Jump to the Detail Series episode.
What RSI measures
RSI measures momentum, not value. It compares the size of recent up moves with recent down moves and turns the result into a number between 0 and 100. A high reading tells you buyers have been pushing harder than sellers lately. It says nothing about whether the price is "too high" or "cheap".
That one idea explains most RSI mistakes. Traders read 70 as "expensive, sell" and 30 as "cheap, buy". In reality, 70 means momentum is strong, and strong momentum often continues.
How RSI is calculated
J. Welles Wilder introduced RSI in 1978. With the default 14 periods:
RSI = 100 − 100 ÷ (1 + RS)
When average gains and losses are equal, RS is 1 and RSI is exactly 50. That is why 50 is the dividing line between bullish and bearish momentum. Wilder used a smoothed average, so each new candle nudges RSI rather than resetting it.
Settings by timeframe
The default of 14 periods with 70 and 30 levels works well almost everywhere. Change it only for a clear reason.
| Use | Length | Levels | Why |
|---|---|---|---|
| Scalping, 1 to 5 minute charts | 7 to 9 | 80 / 20 | Faster reaction; wider levels filter extra noise |
| Day trading, 15 minute to 1 hour | 14 | 70 / 30 | The standard balance of speed and reliability |
| Swing trading, 4 hour to daily | 14 | 70 / 30 | Most widely watched, so levels attract reactions |
| Position trading, weekly | 14 to 21 | 70 / 30 or 65 / 35 | Smoother; extremes are rare, so narrower levels help |
How to read RSI
1. Start with the 50 line
Before looking at 70 or 30, ask where RSI sits relative to 50. Holding above 50 means buyers control momentum; holding below means sellers do. A move back through 50 is often the first sign that control is changing hands.
2. Read RSI in a trend
In a strong uptrend, RSI tends to stay roughly between 40 and 80. Pullbacks that stop around 40 to 50 and turn up are a sign the trend is healthy. In a downtrend the range shifts to about 20 to 60, and rallies that stall near 50 to 60 confirm sellers are still in charge. Readings above 70 in an uptrend show strength, not a sell signal.
3. Read RSI in a range
When price is moving sideways between clear support and resistance, the classic reading works best. RSI near 70 at resistance or near 30 at support suggests the move is stretched within the range. Wait for RSI to turn back inside the level rather than acting the moment it touches.
4. Confirm, don't predict
RSI is most useful as confirmation of what price is already doing. A breakout with RSI pushing above 60 has momentum behind it; a breakout with RSI stuck below 50 deserves suspicion.
Divergence
Divergence is when price and RSI disagree. Price makes a new high, but RSI makes a lower high: the move is continuing on weaker momentum. The mirror image at a low (price lower low, RSI higher low) shows selling pressure fading.
Treat divergence as a warning, not an entry. Strong trends can show divergence several times before turning. It is most reliable when it appears at a level that already matters, such as prior resistance, and when RSI then confirms by crossing back through 50.
Hidden divergence works the other way and points to trend continuation: in an uptrend, price makes a higher low while RSI makes a lower low. The pullback stretched momentum, but the trend structure held.
Common mistakes
- Selling every touch of 70. In an uptrend this means fighting the strongest part of the move.
- Ignoring the 50 line. It is often the most useful level on the indicator.
- Trading divergence on its own. Without a level or confirmation it fires far too early.
- Over-tuning the settings. A setting that fits last month's chart perfectly rarely fits next month's.
- Using RSI without context. Read the trend and key levels on price first, then ask what momentum says.
What to pair RSI with
RSI answers "how strong is the move?". Pair it with tools that answer different questions:
- Moving averages for trend direction, so you know which RSI zone to expect.
- ADX to tell whether the market is trending (read RSI as strength) or ranging (read 70/30 classically).
- MACD as a second momentum view; its zero line plays a similar role to RSI's 50.
- Volume to check whether a breakout that RSI confirms has participation behind it.
- Pivot points or other support and resistance, which give divergence a place to matter.
Go deeper: the Detail Series episode
A slower, podcast-style episode on RSI, covering what it measures, why 50 matters, and when RSI works and when it fails. Good for listening away from the charts.
RSI FAQ
What are the best RSI settings?
The default 14-period RSI with 70 and 30 levels works on most timeframes. Shorter settings such as 7 or 9 react faster but give more false signals; longer settings such as 21 are smoother and slower.
Does RSI above 70 mean I should sell?
No. RSI above 70 means upward momentum is strong. In a trend, RSI can stay above 70 while price keeps rising. Treat it as a sign of strength, and look for a failure or divergence before reading it as a reversal.
Why does the RSI 50 level matter?
50 is the line between average gains and average losses. RSI holding above 50 shows buyers have control of momentum; holding below 50 shows sellers do. Many traders use it as a trend filter.
What is RSI divergence?
Divergence is when price makes a new high or low but RSI does not. It shows momentum is fading behind the move. It is a warning, not a timing signal, and works best at clear support or resistance.