What is the RSI?
The Relative Strength Index is a momentum oscillator developed by J. Welles Wilder in 1978. It measures the speed and magnitude of recent price changes, oscillating on a fixed scale between 0 and 100.
The single question RSI answers is simple: is this move getting exhausted? Rather than telling you where price is, it tells you how much force is behind the recent move — and whether that force is building or fading.
The default setting is 14 periods, and RSI is plotted in a separate pane below the price chart, where its line rises and falls independently of price.
Key point
RSI is bounded between 0 and 100, so it never runs off the chart. That fixed scale is what makes its readings comparable across assets and time — a 30 means the same kind of thing everywhere.
How RSI is calculated
RSI compares the average size of recent gains to the average size of recent losses over the lookback period — 14 by default. The formula is straightforward:
RS = average gain / average loss
RSI = 100 − (100 / (1 + RS))
You don't need to compute this by hand — every charting platform draws RSI automatically. What matters is the intuition behind it: strong, persistent gains push RSI toward 100, while strong, persistent losses push it toward 0.
Rule of thumb
Think of RSI as a tug-of-war score between buyers and sellers over the last 14 bars. The more lopsided the recent action, the closer RSI moves to one extreme.
The 70 / 30 levels
Three reference zones do most of the work when reading RSI. They mark where momentum has stretched far enough that traders start paying attention.
Above 70
Traditionally overbought. The move may be overextended and due for a pause or pullback.
Around 50
Neutral momentum. Neither buyers nor sellers have a clear upper hand over the lookback window.
Below 30
Traditionally oversold. Selling may be exhausted and a bounce is possible.
Critical caveat
Overbought does not mean "sell now," and oversold does not mean "buy now." In strong trends, RSI can stay overbought or oversold for a long time. These zones are warnings to watch, not triggers to act.
RSI in trends vs ranges
The single biggest factor in whether RSI helps or hurts you is the market environment. The same 70/30 reading means opposite things in a range and in a trend.
Ranging market
The 70/30 levels work well as reversal signals. Price bounces between overbought and oversold, so fading the extremes is often profitable.
Trending market
RSI stays pinned in overbought during an uptrend, or oversold during a downtrend, for extended periods. Fading those signals gets you run over.
Adjust your bands
In strong uptrends, some traders shift to 80/40 bands instead of 70/30 — using 40 as a pullback floor and 80 as the genuine overbought line.
RSI divergence — the most powerful signal
Divergence happens when price and RSI disagree — when price keeps moving one way but momentum is no longer following. It is the most respected use of the indicator.
Bullish divergence
Price makes a lower low, but RSI makes a higher low. Downside momentum is weakening, and a reversal up may be near.
Bearish divergence
Price makes a higher high, but RSI makes a lower high. Upside momentum is fading, and a reversal down may be near.
Caveat
Divergence warns that the current trend is losing steam — but it is a warning, not a precise entry. Wait for price confirmation before acting on it.
The centerline (50) strategy
Many trend traders ignore the 70/30 extremes entirely and watch the 50 level instead. The centerline acts as a momentum dividing line that confirms which side is in control.
Above 50 is a bullish bias
When RSI holds consistently above 50, momentum favors buyers. The trend up is being supported by genuine force, not just price drift.
Below 50 is a bearish bias
When RSI stays consistently below 50, momentum favors sellers. Rallies are likely to be sold rather than sustained.
Use crossings to confirm direction
Trend traders use 50 crossings to confirm trend direction rather than betting on 70/30 reversals — letting RSI keep them on the right side of the move.
Common RSI mistakes
Most RSI losses come from a handful of repeated errors. Avoiding these is more valuable than any clever setting.
Shorting every overbought reading in an uptrend
RSI can stay above 70 for weeks in a strong uptrend. Blindly shorting every overbought reading puts you on the wrong side of a powerful move again and again.
Buying every oversold reading in a downtrend
In a falling market, RSI under 30 is not a gift — it is a falling knife. Catching every oversold bounce in a downtrend bleeds your account.
Using RSI alone without price context
RSI is a momentum gauge, not a complete system. Without price structure and trend context, its signals are unreliable and easy to misread.
Ignoring the timeframe
RSI on a 5-minute chart and RSI on a daily chart mean very different things. A reading is only meaningful in the context of the timeframe you are trading.
Treating divergence as an instant entry
Divergence is a heads-up that momentum is fading, not a precise trigger. Acting on it immediately, before price confirms, gets you in too early.
Watch RSI on live charts
Apply what you learned — track momentum on real price data and spot overbought, oversold, and divergence as they form.
The bottom line
The RSI is one of the most useful — and most misused — indicators in technical analysis. Its real value isn't the mechanical "buy oversold, sell overbought" rule that gets beginners run over in trends; it's reading momentum and spotting divergence — moments when price keeps climbing but the energy behind it is quietly draining away. Use RSI to gauge whether a move has conviction, not as a standalone buy or sell button. And always respect the trend: in a strong one, overbought can stay overbought far longer than you can stay solvent fighting it.
Frequently asked questions
What does RSI above 70 mean?+
An RSI reading above 70 traditionally signals that an asset is overbought — meaning the recent up-move may be overextended and due for a pause or pullback. However, overbought does not automatically mean sell. In a strong uptrend, RSI can remain above 70 for extended periods while price keeps rising.
What does RSI below 30 mean?+
An RSI reading below 30 traditionally signals that an asset is oversold — selling pressure may be exhausted and a bounce could follow. But in a strong downtrend, RSI can stay below 30 for a long time. Oversold is a heads-up to watch for a reversal, not an automatic buy signal.
What is RSI divergence?+
Divergence occurs when price and RSI move in opposite directions. Bullish divergence is when price makes a lower low while RSI makes a higher low, hinting that downside momentum is fading. Bearish divergence is when price makes a higher high while RSI makes a lower high, suggesting upside momentum is weakening. Divergence is a warning of a possible reversal, best confirmed by price action.
What is the best RSI setting?+
The default and most widely used setting is 14 periods, as originally designed by J. Welles Wilder. Shorter settings (like 7) make RSI more sensitive and produce more signals with more noise; longer settings (like 21) are smoother and slower. Most traders start with 14 and adjust only with experience.
Can I use RSI by itself to trade?+
RSI works best as one input among several, not in isolation. Used alone, it generates many false signals — especially in trending markets where overbought and oversold conditions persist. Combine RSI with trend direction, support and resistance, and price confirmation for far more reliable results.