By Antonios Fotakis | July 2026
A note before you read: The Relative Strength Index (RSI) is one of the most widely used indicators on any trading platform or screener. It’s also one of the most frequently misunderstood – and most dangerously misused by beginners. This article explains exactly what it measures, how to read it correctly, and – just as importantly – why long-term investors should treat it with significant caution before acting on it.
What is the Relative Strength Index (RSI). Let me ask you something.
Imagine you’re watching a pendulum swing. It goes left, then right, then left again. Back and forth, within a predictable range.
Now imagine the pendulum swings unusually far to the right – further than it has gone in weeks. Does that mean it’s about to swing back to the left? Maybe. That’s how pendulums work – they tend to return toward the centre.
But what if someone installed a new motor that’s pushing it further and further right with each swing? In that case, the fact that it’s at an extreme position isn’t a signal it will reverse. It’s a signal that something fundamentally different is happening.
That’s the essential tension at the heart of RSI. It measures extremes in price momentum – but extreme momentum can mean “about to reverse” or “unusually strong trend that will continue.” The number alone cannot tell you which.
So What Is the Relative Strength Index (RSI), Exactly?
The Relative Strength Index (RSI) is a momentum oscillator – a technical indicator that measures the speed and magnitude of recent price changes to evaluate whether a stock is potentially overbought or oversold.
Developed by J. Welles Wilder Jr. and introduced in 1978, the RSI is calculated from the ratio of average gains to average losses over a specified period – most commonly 14 days.
The formula: Relative Strength Index (RSI) = 100 − (100 ÷ (1 + Average Gain ÷ Average Loss))
The result is always a number between 0 and 100. You don’t need to calculate it manually – every screener and platform does this automatically. What you need to understand is what the number means.
Above 70 = Traditionally considered overbought. The stock has risen significantly in a short period. The RSI signals that buying momentum may be stretched – a potential reversal could follow.
Below 30 = Traditionally considered oversold. The stock has fallen significantly in a short period. The RSI signals that selling momentum may be exhausted – a potential recovery could follow.
Between 30 and 70 = Neutral territory. Neither overbought nor oversold on a momentum basis.
Relative Strength Index (RSI) does not tell you what a company is worth. It tells you how fast its price has been moving in one direction – and whether that movement has been unusually extreme by recent historical standards.
What Relative Strength Index (RSI) Actually Measures – And What It Doesn’t
This distinction is the most important thing to understand about Relative Strength Index (RSI) – and the one most beginners miss entirely.
Relative Strength Index (RSI) is a technical indicator. It analyses price movement. It has no connection to the fundamental quality of the underlying business – its earnings, its revenue growth, its competitive position, its balance sheet.
A great company with strong fundamentals can show an RSI above 70 simply because it has had a strong run of good news and investors have been buying enthusiastically. That doesn’t make it overvalued – it makes it in demand.
A troubled company can show an RSI below 30 because investors have been selling heavily. That doesn’t make it a bargain – it might make it cheap for a very good reason.
This is the critical difference between technical analysis (the study of price movements) and fundamental analysis (the study of the business behind the price) – and RSI is firmly in the technical camp.
Everything we’ve covered in this screener series until now – P/E ratio, EPS, RoIC, profit margin, debt-to-equity – is fundamental analysis. Relative Strength Index (RSI) is something different. It doesn’t ask “is this a good business?” It asks “has this price moved a lot recently?”
Relative Strength Index (RSI) is a measure of momentum, not of value.
The Danger That Nobody Warns Beginners About
Here is where Relative Strength Index (RSI) becomes genuinely dangerous in the hands of someone who doesn’t fully understand it.
The temptation is this: RSI below 30 = oversold = buy. RSI above 70 = overbought = sell. Simple signal. Easy rule. No research required.
The problem is that this mechanical interpretation fails constantly – and the failures tend to be expensive.
Stocks can stay overbought for a very long time. A company in a genuine strong growth phase, reporting exceptional earnings quarter after quarter, can maintain an RSI above 70 for weeks or even months. An investor who sold based on the RSI signal missed the entire continuation of the trend. Every time the RSI reached 70, it seemed to say “too high” – and kept going higher.
Stocks can stay oversold for a very long time. A company in genuine decline – deteriorating fundamentals, losing market share, facing structural headwinds – can maintain an RSI below 30 for extended periods. An investor who bought based on the RSI signal, expecting a bounce, caught a falling knife that kept falling. The RSI said “oversold.” The business was genuinely, fundamentally impaired.
This is the trap that professionals call divergence between technical signals and fundamental reality – and it’s where most beginner trading losses originate.
RSI below 30 is not a buy signal. It’s a flag that says: this stock has been sold heavily recently. Now find out why.
The answer to “why” requires fundamental analysis – the kind of research this entire screener series has equipped you to do. Relative Strength Index (RSI) identifies a situation worth looking at. Your research determines whether it’s an opportunity or a warning.
How Relative Strength Index (RSI) Works Best: Identifying Divergences
Professional technical analysts who use RSI effectively rarely use it as a simple overbought/oversold signal. They use it to identify divergences – situations where the price and the RSI are telling different stories.
Bullish divergence: The stock price makes a new low, but the RSI makes a higher low than it did at the previous trough. Price is still falling; momentum is weakening. This can sometimes signal that the selling pressure is exhausting itself – even before the price reverses.
Bearish divergence: The stock price makes a new high, but the RSI makes a lower high than it did at the previous peak. Price is still rising; momentum is fading. This can sometimes signal that the buying pressure is running out of conviction – even before the price reverses.
Divergences are more nuanced than simple level readings, and they require looking at the RSI chart rather than just a single number. They’re also not reliable in isolation – they work best as one signal among several, confirming or contradicting what fundamental and other technical analysis already suggests.
For most long-term investors, divergence analysis is more tool than they need. But understanding that it exists – and that this is how serious technical analysts actually use RSI – helps calibrate the right level of weight to give the headline overbought/oversold reading on a screener.
Want to understand how to evaluate investment opportunities using both fundamental and technical context? Get the complete Stocks Explained guide here.
Relative Strength Index (RSI) Across Different Time Frames
One detail that screeners often obscure: RSI is time-frame dependent. The standard 14-day RSI tells you about momentum over the past two weeks. A 14-week RSI tells you about momentum over the past three months. These can give very different readings for the same stock.
A stock might have a 14-day RSI of 28 — appearing oversold on short-term momentum – while its 14-week RSI sits at 62 – indicating the longer-term trend remains firmly intact. The short-term reading might reflect a temporary pullback within a healthy longer-term uptrend.
When you see an RSI figure on a screener, always check which time period it uses. Most default to 14 days – but the interpretation changes significantly for shorter or longer periods.
Short-term RSI: More sensitive, more noise, more false signals. Useful for traders with short holding periods. Dangerous for investors making longer-term decisions.
Longer-term RSI: Smoother, fewer signals, more meaningful when they do appear. More relevant context for investors with multi-month or multi-year horizons.
The AF Core Global Position on Relative Strength Index (RSI)
We want to be completely honest about how RSI fits into our investing philosophy — because transparency is what this site is built on.
We do not use Relative Strength Index (RSI) as a primary signal for any of our three categories.
In Fortress, we invest for the long term in broad ETFs and index funds. Short-term momentum readings are irrelevant to a strategy built on decades of compounding. Whether the market’s RSI is 72 or 28 today does not change the fundamental case for staying invested through market cycles.
In Cash Flow, we evaluate dividend stocks based on yield sustainability, dividend growth rate, earnings quality, and balance sheet health. A low RSI on a dividend stock might make us look more closely at whether the recent selloff has created an attractive entry point — but only after fundamental analysis confirms the dividend is intact and the business is sound.
In High Voltage, we occasionally note RSI context for picks that have experienced significant short-term price movements – as one piece of the picture, never as the decision driver. A High Voltage pick with a strong fundamental case and a short-term RSI below 30 after an overreaction to a news event might represent a better entry point than the same stock at RSI 65. But the fundamental case comes first, always.
Relative Strength Index (RSI) is a contextual tool. For long-term investors, it belongs in the background – a filter for timing refinement, never for investment selection.
Not blind trust. Informed choice.
What to Look For When You See Relative Strength Index (RSI) on a Screener
When Relative Strength Index (RSI) appears in your research, treat it as the beginning of a question, never the end of an answer:
Is the RSI above 70 or below 30? Note it – then immediately ask why. What has happened fundamentally to drive that momentum? Strong earnings, bad news, sector rotation, macro event?
What does the fundamental picture say? An RSI below 30 on a company with deteriorating fundamentals is a falling knife. The same reading on a fundamentally strong company after an overreaction to temporary bad news might be a genuine entry opportunity.
What time frame is this Relative Strength Index (RSI)? The 14-day default is short-term noise for most long-term investors. Consider whether a longer-term RSI reading gives more useful context for your holding period.
Is the RSI diverging from the price trend? Bullish divergence during a downtrend, or bearish divergence during an uptrend, is more meaningful than a simple level reading. Look at the chart, not just the number.
Have you done the fundamental research first? Relative Strength Index (RSI) should confirm or add nuance to a fundamental conclusion. It should never replace one.
For a complete guide to evaluating stocks and building a real investment case using both fundamental and contextual analysis, our Stocks Explained guide covers everything you need. 👉 Get the Stocks Explained Guide Here
Nothing in this article constitutes financial advice. All content is for informational and educational purposes only. Always do your own research before making any investment decision.
