MomentumLeading momentum oscillatorRSI

Relative Strength Index RSI

The 0–100 momentum gauge that flags overbought and oversold conditions.

Quick answer: The RSI is a momentum oscillator that measures the speed and size of recent price changes on a 0–100 scale, flagging a market as overbought above 70 and oversold below 30.

In simple words

RSI compares how much a stock or index has risen on its up days versus how much it has fallen on its down days over the last 14 bars, then squeezes that into a single number between 0 and 100. A high RSI (above 70) means buyers have been in strong control and the move may be stretched; a low RSI (below 30) means sellers have dominated and the fall may be overdone. Most traders use it to spot when a market is running too hot or too cold, and to catch momentum divergences before price turns.

Relative Strength Index — visual

How Relative Strength Index looks on a chart

RSI oscillates between 0 and 100. Readings above 70 mark overbought conditions, below 30 oversold; the 50 line separates bullish from bearish momentum.

Professional explanation

What RSI actually measures

RSI is the ratio of average gains to average losses over a look-back period, normalised onto a 0–100 scale. It does not measure the strength of one stock against another — despite the name — but the strength of a market against its own recent history. A rising RSI says up-moves are getting larger relative to down-moves; a falling RSI says the opposite. Because it reacts to the most recent bars, it can turn before price does, which is why it is classed as a leading indicator.

The 70/30 levels and the 50 midline

Wilder's original overbought/oversold thresholds are 70 and 30. But these are not automatic sell/buy signals: in a strong Nifty uptrend RSI can sit above 70 for days, and in a sharp fall it can stay pinned below 30. The 50 line is just as useful — momentum is broadly bullish above 50 and bearish below it, so many trend traders use a 50 cross as a filter rather than trading the 70/30 extremes blindly.

Divergence: RSI's most valued signal

The signal professionals prize most is divergence. Bearish divergence is when price makes a higher high but RSI makes a lower high — the new price peak is not backed by stronger momentum, warning of exhaustion. Bullish divergence is the mirror image at a bottom. Divergence is a warning, not a trigger: it can persist for a long time in a strong trend, so it works best combined with a price-based confirmation.

Why the period matters

The default is 14 periods. A shorter period (7–9) makes RSI more sensitive and noisier — more signals, more false ones — suited to intraday scalping. A longer period (21) smooths it, giving fewer but more reliable readings for positional trading. Changing the period changes how often RSI reaches 70/30, so the thresholds and the setting must be tuned together.

Formula

Relative Strength Index formula

RSI = 100 − 100 / (1 + RS), RS = Average Gain / Average Loss

Averages use Wilder's smoothing over N periods (default 14). Average Gain is the mean of up-closes, Average Loss the mean of down-closes.

RS — Relative Strength — average gain divided by average loss over N periods
Average Gain — Wilder-smoothed mean of the positive close-to-close changes
Average Loss — Wilder-smoothed mean of the negative close-to-close changes (as a positive number)
N — Look-back period, default 14 bars

How it is calculated

For each bar, find the change from the previous close; separate it into a gain (if up) or a loss (if down).
Compute the first Average Gain and Average Loss as simple averages over the first N periods.
For every later bar, smooth: Average Gain = (prior Average Gain × (N−1) + current gain) / N, and the same for loss.
Compute RS = Average Gain / Average Loss.
Compute RSI = 100 − 100 / (1 + RS). The result is bounded between 0 and 100.

Interpretation & signals

Traders watch three things: whether RSI is above 70 (overbought) or below 30 (oversold), whether it is above or below the 50 midline (momentum bias), and whether it diverges from price (early reversal warning).

Buy / bullish signals

RSI crosses back up through 30 from oversold, signalling selling may be exhausted.
Bullish divergence: price makes a lower low but RSI makes a higher low.
In an uptrend, RSI pulls back to the 40–50 zone and turns up (a trend-continuation entry).
RSI crosses above 50, confirming momentum has flipped bullish.

Sell / bearish signals

RSI crosses back down through 70 from overbought.
Bearish divergence: price makes a higher high but RSI makes a lower high.
In a downtrend, RSI rallies to 50–60 and rolls over.
RSI crosses below 50, confirming momentum has flipped bearish.

False signals to beware

Overbought in a strong trend: RSI can hold above 70 for many bars while price keeps rising — shorting it is a classic trap.
Divergence in a powerful trend can repeat several times before price finally turns.
On very short periods, 70/30 crosses fire constantly and most are noise.

Settings, timeframe & conditions

Best settings

14 periods, 70/30 levels (Wilder default)

Avoid

Trading 70/30 crosses blindly in a trending market

Works best in

Range-bound or gently trending markets

Struggles in

Strong, one-way trends (stays pinned at extremes)

Advantages & limitations

Advantages

Bounded 0–100 scale makes overbought/oversold easy to read and compare across instruments.
Divergence gives an early warning that trend-following tools miss.
Works on any timeframe and any liquid instrument.
Simple, widely understood, and available on every charting platform.

Limitations & disadvantages

Gives premature and repeated signals in strong trends.
Overbought/oversold thresholds are arbitrary and instrument-dependent.
As a single-line oscillator it ignores volume and the broader context.
Whipsaws badly on short settings in choppy markets.

Combining Relative Strength Index with other indicators

Exponential Moving Average — Use a 50/200 EMA to define the trend, then take only the RSI signals that align with it — RSI dips in an uptrend, RSI rallies in a downtrend.
Moving Average Convergence Divergence — MACD confirms the momentum shift RSI hints at; agreement between the two is a stronger signal than either alone.
Bollinger Bands — RSI extremes that coincide with a tag of the outer Bollinger Band mark high-probability mean-reversion points.

Practical examples (Nifty & Bank Nifty)

NIFTY example

Nifty rallies from 23,800 to 24,600 and RSI(14) pushes to 78 — overbought. A patient trader does not short the strength; instead they wait. Two days later Nifty prints a marginally higher high at 24,650 but RSI only reaches 71 — a bearish divergence. That combination of an overbought reading plus a failure to confirm the new high is the warning; a break of the prior swing low then confirms the pullback.

BANKNIFTY example

Bank Nifty sells off from 52,000 to 50,200 and RSI(14) drops to 24 — oversold. Rather than catching the falling knife, a trader waits for RSI to climb back above 30 while price holds above the previous session's low. That RSI recovery through 30, confirmed by price, is the cue that selling pressure has eased — Bank Nifty's higher volatility means its RSI reaches extremes faster than Nifty's.

Common mistakes

Treating 'overbought' as an automatic sell — in a trend it is a sign of strength, not weakness.
Acting on divergence alone without waiting for price to confirm.
Using the 14-period default on a 1-minute chart and drowning in false signals.
Forgetting that RSI thresholds should shift: 80/40 suits strong uptrends better than 70/30.

Professional usage

Institutional and professional traders rarely trade RSI's 70/30 crosses mechanically. They use RSI as a momentum context tool: to grade the strength of a trend (does each new high come with a higher RSI peak?), to time entries within an established trend using the 40–60 zone, and above all to hunt divergence at potential turning points. It is almost always combined with trend and price-structure analysis, never used as a standalone trigger.

Key takeaway

RSI is the market's momentum thermometer: above 70 it is running hot, below 30 it is running cold, and when it disagrees with price (divergence) it is warning of a turn. Read it in the context of the trend — in a strong move, respect the extreme; in a range, fade it.

Frequently asked questions

What is the RSI indicator?

The Relative Strength Index is a momentum oscillator, created by J. Welles Wilder in 1978, that measures the speed and magnitude of recent price changes on a 0–100 scale. Readings above 70 are considered overbought and below 30 oversold.

What is a good RSI setting?

The standard is 14 periods with 70/30 overbought/oversold levels. Shorter periods (7–9) are more sensitive for intraday trading; longer periods (21) are smoother for positional trading.

Is RSI a leading or lagging indicator?

RSI is generally a leading indicator — because it reacts to the most recent bars, it can turn before price, especially through divergence. However, it still relies on past prices, so it is not predictive in isolation.

What does RSI above 70 mean?

It means the market is overbought — recent gains have been large relative to losses. It signals that a move may be stretched, but in a strong trend RSI can stay above 70 for a long time, so it is not an automatic sell.

What does RSI below 30 mean?

It means the market is oversold — recent losses have dominated. It flags that a fall may be overdone, but in a strong downtrend RSI can remain below 30, so it should be confirmed by price before buying.

What is RSI divergence?

Divergence is when price and RSI move in opposite directions. Bearish divergence (price higher high, RSI lower high) warns of a top; bullish divergence (price lower low, RSI higher low) warns of a bottom. It is a warning, not a trigger.

What is the 50 line on RSI?

The 50 level is the momentum midline. RSI above 50 shows bullish momentum, below 50 bearish. Many trend traders use a 50 cross as a filter instead of trading the 70/30 extremes.

Which is better, RSI or MACD?

Neither is universally better. RSI is a bounded oscillator best for overbought/oversold and divergence; MACD is an unbounded trend-momentum tool best for crossovers and trend strength. Many traders use them together for confirmation.

What is the best RSI setting for intraday trading?

Intraday traders often shorten RSI to 7–9 periods for faster signals on 5- or 15-minute charts, and may widen the levels to 80/20 to reduce noise. The 14-period default remains a solid all-round choice.

Can RSI be used for Nifty and Bank Nifty?

Yes. RSI works on any liquid instrument. Because Bank Nifty is more volatile, its RSI reaches 70/30 extremes faster than Nifty's, so some traders use 80/20 levels on Bank Nifty.

Why does RSI stay overbought in an uptrend?

In a strong uptrend, up-closes consistently outweigh down-closes, keeping the RS ratio high and RSI above 70. This is a sign of trend strength, not an imminent reversal — which is why shorting overbought RSI in a trend fails.

Does RSI repaint?

No. RSI is calculated on closed bars, so a completed bar's RSI value does not change. The current forming bar's RSI updates in real time until the bar closes, which is normal, not repainting.

Voice search & related questions

Natural-language questions people ask about Relative Strength Index.

What is RSI in simple words?

RSI is a number from 0 to 100 that tells you whether a market has been rising too fast (above 70, overbought) or falling too fast (below 30, oversold) recently.

Is RSI 30 a buy signal?

RSI at 30 means oversold, which can precede a bounce, but it is not an automatic buy. In a strong downtrend RSI can stay below 30; wait for it to cross back above 30 with price confirming.

What RSI level is best to buy?

Many traders look to buy when RSI turns up from below 30 in a range, or pulls back to the 40–50 zone and rises in an uptrend — always confirmed by price, not on the RSI number alone.

Is a high RSI good or bad?

A high RSI shows strong recent buying, which is good for trend followers but a caution for mean-reversion traders, since the move may be stretched.

How do I use RSI for day trading?

For day trading, shorten RSI to about 7–9 periods on a 5- or 15-minute chart, use it to spot overbought/oversold turns and divergence, and confirm every signal with price action.

Sources & references

Last reviewed 8 July 2026. Educational content only — not investment advice.