RSI Calculator: Measure Relative Strength Index Instantly

Master the Market with Our Free Online RSI Calculator

The Relative Strength Index (RSI) calculator is a powerful trading instrument designed to identify potential market turning points. It signals whether a stock is in an overbought state, possibly facing a price correction, or in an oversold condition, potentially poised for a rally. This momentum indicator empowers traders with insights for strategic entry and exit decisions. This guide will explain the RSI, its calculation formula, and how to effectively utilize our advanced online calculator.

Understanding the Relative Strength Index (RSI)

The RSI is a momentum oscillator that analyzes the magnitude of recent price gains and losses over a defined period. Its core function is to gauge the speed and change of price movements, helping to assess whether an asset's current trend is sustainable or likely to reverse.

Financial instruments like stocks, bonds, and commodities fluctuate in value through economic cycles. By measuring momentum, traders can attempt to pinpoint shifts from bullish to bearish phases, or vice versa. This knowledge can be crucial for selling before a downturn or buying ahead of an upswing.

This indicator computes a value ranging from 0 to 100, with 50 as a central equilibrium line. A reading above 50 generally suggests positive momentum and potential for continued price increases. Conversely, an RSI below 50 indicates negative momentum and the possibility of further price declines. The further the value moves from 50, the stronger the momentum signal.

Interpreting RSI Readings

For a standard 14-period RSI, traders focus on two key thresholds:

• An RSI reading at or above 70 typically suggests an overbought condition. This signals that the upward price trend may be exhausted and a downward reversal could be imminent, representing a potential sell signal.
• An RSI reading at or below 30 usually indicates an oversold condition. This implies that the downward price move may be overextended and a price increase could be forthcoming, representing a potential buy signal.

Consider a real-world scenario from late 2020 involving Synnex stock. Between October 30 and November 12, some investors sold their holdings, fearing a crash after a significant price run-up. However, the RSI on November 12 was 57.64—below the 70 overbought threshold. An investor using our scientific calculator might have held the stock, which subsequently rose to $162.82, yielding a 23.69% gain.

The RSI Calculation Formula

The RSI is derived from average price changes over a selected period, using these two core formulas:

1. First, calculate the Relative Strength (RS): RS = Average Gain / Average Loss
2. Then, calculate the RSI: RSI = 100 - [100 / (1 + RS)]

The 'Average Gain' is the average of all positive price changes during the period, while the 'Average Loss' is the average of all negative price changes (expressed as absolute values). A typical default period is 14 days.

Here is a simplified calculation process:

1. Record the closing prices for 15 consecutive days to get 14 price changes.
2. Separate the daily gains (positive changes) from the daily losses (negative changes).
3. Calculate the average gain and the average loss over the 14 days.
4. Compute the RS value by dividing the average gain by the average loss.
5. Plug the RS value into the RSI formula.

For subsequent RSI values after the first calculation, a smoothing formula is often used: New Average = [(Previous Average x 13) + Current Price Change] / 14. This applies to both the average gain and average loss, allowing the RSI curve to be plotted over time.

Applying RSI with Other Indicators: A Practical Example

For more reliable signals, the RSI is often combined with other tools like Simple Moving Averages (SMA). Let's examine the SPY ETF in March 2020 using RSI alongside 7, 20, and 50-day SMAs.

The price peaked in February 2020 before a sharp decline. Analysis shows a bearish RSI divergence occurred early on, where the price made a higher high while the RSI made a lower high, indicating weakening upward momentum. This was followed by the price crossing below key moving averages (7-SMA and 20-SMA) while the RSI was below 50, providing a sell signal.

Later, the RSI entered the oversold region (below 20 in this adjusted example), hinting at a potential trend change. However, price confirmation came only when the RSI broke above a key trendline and, crucially, when the 7-day SMA crossed above the 20-day SMA, confirming a buy signal. This multi-indicator approach could have helped investors navigate the volatile period.

Frequently Asked Questions