The Relative Strength Index (RSI) is a momentum indicator that oscillates between 0 and 100, designed to measure the magnitude of recent price changes and evaluate overbought or oversold conditions. Developed by J. Welles Wilder in 1978, RSI has become one of the most widely used technical analysis tools among traders and investors. It answers a straightforward question: is this asset priced too high relative to its recent performance, or too low?
How It Works
RSI compares the average of recent gains to the average of recent losses over a set period—typically 14 trading days, though investors can adjust this timeframe. The formula produces a single number between 0 and 100. Readings above 70 generally indicate overbought conditions (suggesting a potential price pullback), while readings below 30 suggest oversold conditions (suggesting potential upside). An RSI of 50 represents a neutral midpoint with no directional bias.
The calculation itself is straightforward: RSI = 100 - (100 / (1 + RS)), where RS equals the average gain divided by the average loss. Most trading platforms calculate this automatically, so you only need to interpret the results.
Why It Matters for Investors
For angel investors and HNW individuals evaluating entry and exit points, RSI provides objective quantitative signals rather than relying purely on price charts or sentiment. It's particularly useful when analyzing volatile startup investments or growth stocks that experience sharp swings. RSI helps confirm trends—a rising stock with rising RSI suggests strong momentum, while divergences (price making new highs while RSI fails to do so) often precede reversals.
RSI works best as a confirmation tool rather than a standalone decision-maker. Combining it with moving averages or support and resistance levels significantly improves accuracy. During strong trending markets, RSI can remain overbought or oversold for extended periods, so context matters.
Example
Imagine a promising fintech startup's stock price rises from $50 to $75 in two weeks. RSI climbs to 82, signaling overbought conditions. Rather than buying at the peak, a savvy investor might wait for RSI to fall below 70, indicating the initial enthusiasm has cooled and a better entry point may emerge. Alternatively, if RSI drops to 25 during a market panic, it could signal an attractive buying opportunity.
Key Takeaways
- RSI measures momentum on a 0-100 scale; above 70 = overbought, below 30 = oversold
- Use it as a confirmation tool alongside other technical indicators, not as your sole decision criterion
- 14-period RSI is standard, but adjust based on your trading timeframe and investment style
- Watch for divergences where price and RSI move in opposite directions—these often precede significant moves