Beginner’s guide: What is the RSI indicator & how to use the RSI formula effectively?

When it comes to technical analysis, there is a range of indicators you can use to help guide your trading decisions. The relative strength index (RSI) is one such popular indicator used in stock chart analysis. It serves as a momentum oscillator that measures the speed and rate of change of price movements.

This guide will explain what the RSI indicator is, how it is calculated, how to interpret it, and how to effectively use it in your trading or analysis.

What is The Relative Strength Index?

The relative strength index was developed by J. Welles Wilder in 1978. It measures the magnitude and velocity of directional price movements and then translates that into a numerical value ranging between 0 and 100. The closer the RSI value is to 0, the weaker the momentum. The closer it is to 100, the stronger the momentum.

RSI compares the average gains and losses over a specified lookback period. It shows whether an asset is overbought or oversold relative to recent price performance. The default RSI settings use a 14-day lookback period with the average gains and losses calculated using the default parameters.

The RSI formula looks complex but is straightforward once broken down:

RSI = 100 - (100/(1 + RS))

Where,

RS = Average gain over past 14 days/Average loss over past 14 days

Average gain = Sum of gains over past 14 days/14

Average loss = Sum of losses over past 14 days/14

How is RSI Calculated?

The RSI calculation process can be broken down into a 7-step process

Step 1) Determine price change for each period (such as daily closing prices)

Step 2) Classify each period as up/positive or down/negative based on price change

Step 3) Determine average gain over the lookback period (14 days default)

Step 4) Determine average loss over the lookback period

Step 5) Calculate relative strength = Average gain/Average loss

Step 6) Calculate RSI = 100 - (100/(1 + RS))

Step 7) Plot the RSI values on a scale of 0 to 100

The RSI formula only considers the magnitude of gains and losses, not the direction. Gains are summed and averaged separately from losses.

As the average gain increases relative to the average loss, the RSI value moves higher. The opposite causes RSI to move lower.

Example of RSI Calculation

Consider a 14-day period with the following hypothetical gains and losses:

Day 1: Gain of 1
Day 2: Loss of 4
Day 3: Gain of 2
Day 4: Loss of 2
Day 5: Gain of 3
Day 6: Gain of 1
Day 7: Loss of 2
Day 8: Loss of 5
Day 9: Gain of 2
Day 10: Gain of 4
Day 11: Loss of 1
Day 12: Gain of 2
Day 13: Loss of 3
Day 14: Gain of 1

Total gain = 16
Total loss = 17

Average gain = Total gain/14
      = 16/14
      = 1.14

Average loss = Total loss/14
      = 17/14
      = 1.21

RS = Average gain/Average loss
  = 1.14/1.21
  = 0.942

RSI = 100 - (100 / (1 + RS))
  = 100 - (100 / (1 + 0.942))
  = 100 - (100 / 1.942)
  = 100 - 51.49
  = 48.51

Therefore, the 14-day RSI value for this hypothetical period is 48.51.

This step-by-step example demonstrates how to practically calculate the RSI value from price data using the basic RSI formula.

How to Interpret the RSI Indicator

The RSI indicator offers traders and analysts several ways to interpret and utilise its value. Here are the main methods:

Overbought (Above 70)/Oversold (Below 30)

RSI readings above 70 indicate an asset is overbought while readings below 30 indicate an asset is oversold. This signals potential trend reversals or corrective pullbacks.

Bullish/Bearish Divergence

Divergence occurs when RSI forms highs and lows that do not align with price. This divergence signals potential reversals.

Failure Swings

Failure swings are when RSI reaches overbought or oversold and then reverses direction. This flags potential trend continuations.

Trend Confirmation

RSI can confirm uptrends when above 50 and downtrends when below 50. Trend strength increases when RSI reaches overbought or oversold zones.

Centreline Crossovers

RSI crossing above or below the 50 centreline can signal a trend change. It reflects shifting momentum.

RSI Trading Strategies

Some common trading strategies utilising RSI include:

• Buying oversold and selling overbought levels
• Fading failure swings
• Trading bullish/bearish divergence
• Using centreline crossovers
• Confirming breakouts when RSI reaches overbought or oversold zones

Tips for Using RSI Effectively

1. Use with confirmation
Combine RSI with other indicators or analysis for confirmation. RSI alone is prone to false signals.

2. Watch for divergence
The divergence between RSI and price is a powerful signal worth acting on.

3. Adjust parameters
Tweak the RSI lookback period and overbought/oversold levels to better detect trends in a particular security.

4. Fit RSI to market conditions
More volatile markets may need a shorter RSI period, while less volatile markets can use longer periods.

5. Use on multiple timeframes
Analyse RSI across short, medium, and long-term timeframes for a robust read.

6. Consider both signal line and bars
Watch both the RSI line and histogram bars for insight. The bars show momentum direction.

7. Focus on failure swings and crosses
Failure swings above 70 or below 30 and centreline crosses at 50 are high-probability signals.

Mastering the usage of the RSI indicator takes practice. RSI works best when blended into a broad analysis approach including various technical and fundamental factors.

Conclusion

The RSI indicator offers traders a useful momentum tool to spot potential reversals and gauge trend strength. Its bounded range and clear overbought/oversold signals provide helpful insight into market dynamics.

Make sure to combine RSI with other indicators and analysis methods. Adjust it to fit different markets and timeframes. With practice, RSI can aid in making lucrative trading decisions.