What is the RSI in the stock market and how is it interpreted?

Updated June 27, 2026 · DeepTicker

The RSI (Relative Strength Index) is a technical indicator that measures the speed and magnitude of recent price moves on a scale of 0 to 100. It is used to detect whether a stock is overbought (RSI above 70) or oversold (RSI below 30). It is one of the most widely used oscillators in technical analysis.

What RSI (Relative Strength Index) is and why it matters

The RSI in the stock market, short for Relative Strength Index, is a technical indicator created by J. Welles Wilder in 1978 that has become one of the most popular in the world. Its job is to measure, on a bounded scale of 0 to 100, how strongly a stock's price has risen or fallen over a recent period. In other words, it does not measure the value of the company, but the momentum of the price: if recent rises are intense, the RSI goes up; if falls dominate, the RSI goes down.

To understand what the RSI is it helps to know that it belongs to the family of oscillators, indicators that move within a fixed range. Unlike a moving average, which can go to infinity, the RSI always lives between 0 and 100, which makes extreme values easy to interpret. By convention, Wilder calculated the RSI over 14 periods (14 days if the chart is daily), a parameter that remains the most widely used standard, although some traders adjust it to 7 or 21 depending on their style.

The best-known reading of the RSI is the overbought and oversold zones. When the RSI rises above 70, the stock is said to be overbought: it has risen a lot and very fast, and could be ripe for a correction or a pause. When the RSI falls below 30, it is said to be oversold: it has fallen sharply and could be ready for a bounce. These thresholds are not laws, but guidelines that warn that the recent move has been extreme.

The RSI matters because it puts a number on something that would otherwise be purely visual and intuitive: how far the price has stretched in one direction. An investor looking at a chart may perceive that a stock has risen a lot, but the RSI quantifies it objectively and comparably. This makes it useful above all for short- and medium-term traders looking for entry or exit points based on momentum, rather than on the value of the business.

It is crucial to understand what kind of information the RSI gives and, above all, what it does not. The RSI is a technical analysis indicator: it only looks at the price and its recent history. It knows nothing about the company's profits, its debt, its competitive advantage or whether it is expensive or cheap relative to its value. A high RSI does not mean the stock is good, nor a low RSI that it is bad. It measures exclusively the recent behaviour of the price.

Another widely followed signal of the RSI are divergences. A bearish divergence occurs when the price marks a higher high but the RSI marks a lower high: the price rises, but with less internal strength, which some traders read as exhaustion of the trend. The bullish divergence is the opposite: the price makes a lower low but the RSI a higher low, suggesting the fall is losing momentum. Divergences are among technical analysts' favourite tools, although, like everything in technical analysis, they fail often.

It pays to put the RSI in its proper place within the investor's landscape. For someone who trades, it is a valuable timing tool. For someone who invests in companies over the long term, its usefulness is marginal: a great company can spend months with the RSI overbought while it keeps rising, and a terrible company can be oversold and keep falling for years. The RSI describes the rhythm of the price, not the destiny of the business.

Finally, the RSI behaves very differently depending on the market context. In a sideways range, where the price oscillates between supports and resistances, the overbought and oversold signals work reasonably well. But in a strong trend, the RSI can stay stuck in extreme zones for a long time without the price reversing: in a powerful rise, the RSI can live above 70 for entire weeks. Ignoring this and selling just because the RSI marks 75 is one of the most costly mistakes with this indicator.

How RSI (Relative Strength Index) is calculated

RSI = 100 − [100 / (1 + RS)] · RS = Average gain / Average loss (over N periods, usually 14)

· RS (Relative Strength): the ratio between the average gain and the average loss of the last N periods; it is the heart of the calculation.
· Average gain: the average of the positive price changes (the days that close higher) over the period considered.
· Average loss: the average of the negative changes (the days that close lower), taken in absolute value.
· N (periods): the number of sessions over which it is calculated; Wilder's standard is 14, although 7 (more sensitive) or 21 (smoother) are also used.
· Result: a value between 0 and 100; the higher, the more recent rises have dominated; the lower, the more recent falls have dominated.

Example of RSI (Relative Strength Index)

Imagine a stock that over the last 14 sessions has had an average daily gain of €1.20 on the up days and an average loss of €0.40 on the down days. The RS (relative strength) is 1.20 / 0.40 = 3. Applying the formula: RSI = 100 − [100 / (1 + 3)] = 100 − 25 = 75. An RSI of 75 is above the threshold of 70, so the stock is considered overbought: it has risen with much more strength than it has fallen, and a technical trader would interpret that it could be ripe for a pause or correction.

Now suppose that after several weeks of falls the average gain drops to €0.30 and the average loss rises to €1.10. The RS is 0.30 / 1.10 = 0.27, and the RSI = 100 − [100 / (1 + 0.27)] = 100 − 78.7 = 21. An RSI of 21 is below 30, in oversold territory: the falls have clearly dominated and the stock could be ready for a bounce. But beware: in a strong downtrend, that low RSI can persist for weeks while the price keeps falling. Oversold warns that the move is extreme, not that it is about to reverse.

How to interpret RSI (Relative Strength Index)

→The RSI moves between 0 and 100: above 70 indicates overbought and below 30 oversold.
→Overbought and oversold warn that the move has been extreme, not that it is about to reverse immediately.
→In strong trends the RSI can stay in extreme zones for a long time without the price reversing.
→Divergences between the price and the RSI are signals of possible exhaustion of the trend, although they fail frequently.
→The standard period is 14; shorter periods make it more sensitive and longer ones smooth it.
→The RSI measures only the price: it knows nothing about the quality or the valuation of the business.

Common mistakes with RSI (Relative Strength Index)

✕Selling automatically just because the RSI exceeds 70, ignoring that in strong trends it can keep rising for weeks.
✕Buying just because the RSI drops below 30, without looking at whether the company is falling due to a real business problem.
✕Using the RSI in isolation, without taking into account the general trend or the market context.
✕Overfitting the parameters (period and thresholds) until they fit the past, something that rarely works going forward.
✕Confusing a technical timing indicator with a value criterion: the RSI does not tell you whether a company is good or whether it is expensive.

What a high or low RSI means: overbought and oversold

A high RSI (above 70) indicates that the price has risen strongly and steadily in the recent period: the stock is overbought. The classic reading is that the upward move could be running out of steam and a correction or pause could be approaching. Some traders use stricter thresholds, such as 80, for very volatile markets where 70 is reached too easily.

A low RSI (below 30) indicates the opposite: the falls have dominated and the stock is oversold. The usual interpretation is that the fall could be running out of steam and a bounce could be possible. Again, some traders lower the threshold to 20 to filter signals in very nervous markets.

The most widespread mistake is treating these thresholds as automatic buy or sell orders. Overbought and oversold do not mean 'reverse now', but 'this move has been extreme'. In a strong trend, an RSI can remain overbought or oversold for a long time while the price follows its course. That is why experienced traders use the RSI as a context alert, not as an isolated trigger.

RSI versus other technical indicators (MACD, moving averages)

The RSI measures momentum within a bounded range of 0 to 100, which makes it especially good at detecting extremes. The MACD, another very popular oscillator, measures the difference between two moving averages and focuses more on trend changes and crossovers. They are not rivals, but complementary: many traders use them together to confirm signals and reduce false alerts.

Moving averages offer a different perspective: instead of measuring the strength of the move, they mark the direction of the trend by smoothing out price noise. A common approach is to combine the direction given by the moving average with the momentum given by the RSI: for example, looking for RSI oversold only when the general trend, according to the moving average, is still upward, so as not to buy in the middle of a structural fall.

The general lesson is that no technical indicator works well on its own. The RSI shines at detecting extremes and divergences, but combined with other tools and, above all, with knowledge of the market context. Piling up many indicators is not the solution either: beyond a certain point they overlap and generate paralysis. Better few, well understood and used with judgement.

Limitations of the RSI: why it fails and when not to trust it

The most important limitation of the RSI is that, in strong trends, the overbought and oversold signals fail systematically. A stock in the middle of an uptrend can keep the RSI above 70 for weeks, generating one sell signal after another that turn out to be premature. Whoever sells just because of a high RSI in a powerful trend usually misses much of the rise.

The second limitation is that the RSI, like all technical analysis, only looks at the price. It incorporates no information about the business: not results, not debt, not competitive advantage, not valuation. It can give an attractive oversold signal on a company that is falling precisely because its business is deteriorating, a value trap that the RSI is unable to detect.

The third limitation is the subjectivity of the parameters. Changing the period from 14 to 7 or the thresholds from 70/30 to 80/20 completely alters the signals, and it is always possible to adjust the indicator until it 'would have worked' in the past. That retrospective overfitting is a classic trap: what fits the history perfectly rarely works as well going forward. The RSI is a tool of probabilities, not a crystal ball.

RSI and fundamental analysis: how DeepTicker combines them

The RSI answers a very specific question: has the price moved with too much strength in the short term? It is a timing question, useful above all for short- and medium-term trading. But it leaves unanswered the two questions that really determine whether an investment makes sense over the long term: is the company good? and is it expensive or cheap? That is where DeepTicker complements what the RSI cannot see.

To know whether the company is good, DeepTicker's DeepScore summarizes its quality in a 0 to 100 grade across five dimensions, with sector benchmarks, rewarding competitive advantage (moat) and return on capital. And to know whether it is expensive or cheap, the Reverse DCF (which discounts cash flows) shows you what growth and what margin the current price is already pricing in, instead of giving you an opaque number. The RSI tells you whether the price is stretched today; the DeepScore and the Reverse DCF tell you whether the business behind it is worth it.

Combining them is the sensible thing to do. An oversold stock (low RSI) on a company with a good DeepScore and a Reverse DCF of modest expectations is very different from an equally oversold stock on a fragile, expensive business: the first can be an opportunity and the second a trap. DeepTicker gives you serious fundamental analysis in a simple way and with every figure explained, so you learn not to confuse a technical bounce with a good investment. This is educational information, not financial advice.

On DeepTicker you get this metric calculated and explained for thousands of stocks, with no spreadsheets.

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Frequently asked questions about RSI (Relative Strength Index)

What is the RSI in the stock market?

The RSI (Relative Strength Index) is a technical indicator that measures the speed and magnitude of recent price moves on a scale of 0 to 100. It is used to detect overbought and oversold zones.

How is the RSI calculated?

With the formula RSI = 100 − [100 / (1 + RS)], where RS is the ratio between the average gain and the average loss of the last periods, usually 14 sessions. The result is always between 0 and 100.

What does an RSI above 70 mean?

It indicates overbought: the price has risen strongly and steadily, and could be ripe for a correction or pause. It is not an automatic sell order, but a warning that the move has been extreme.

What does an RSI below 30 mean?

It indicates oversold: the falls have dominated and the stock could be ready for a bounce. In strong downtrends, however, it can stay low for weeks while the price keeps falling.

Which RSI period is best?

The standard is 14 periods, as Wilder proposed. Shorter periods (7) make it more sensitive and generate more signals; longer periods (21) smooth it. It depends on the style and horizon of each trader.

What is a divergence in the RSI?

It occurs when the price and the RSI go in opposite directions: for example, the price marks a higher high but the RSI a lower one. It is interpreted as a loss of strength in the trend, although it fails often.

Is the RSI useful for long-term investing?

Its usefulness for the long term is marginal. The RSI measures short-term price momentum, not the quality or the valuation of the business. A great company can be overbought for months and keep rising.

Is the RSI reliable?

It is a tool of probabilities, not of certainties. It works better in sideways ranges than in strong trends, and fails frequently if used on its own. It pays to combine it with context and with analysis of the business.

Educational content by DeepTicker. This is not financial advice or a recommendation to buy or sell. Investing involves risk of loss.