LSI / RSI Calculator

The Relative Strength Index (RSI) Calculator estimates market momentum. Simply enter your price series and lookback period to calculate your Relative Strength Index and related metrics. This tool helps traders better understand recent price movements to spot potential trends. This calculator also calculates Relative Strength (RS) and average gains and losses.

Enter closing prices separated by commas or new lines (e.g., 100, 102, 101)
Enter the number of periods to average (typically 14 days)

This calculator provides estimates only. It is not intended to provide financial advice. Consult a financial advisor for personalized guidance.

What Is Relative Strength Index

The Relative Strength Index (RSI) is a tool that measures how fast prices are changing. It looks at recent price gains and losses to see if a stock is bought too much or sold too much. The result is a number between 0 and 100. Traders use this number to guess if the price might go up or down next.

How Relative Strength Index Is Calculated

Formula

RSI = 100 − (100 / (1 + RS))

Where:

  • RS = Average Gain / Average Loss
  • Gain = Price increase (current - previous)
  • Loss = Price drop (previous - current, made positive)

The calculator first looks at how much the price went up or down each day. It finds the average gain and the average loss over the chosen time period. Then, it divides the average gain by the average loss to get the Relative Strength (RS). Finally, it plugs the RS into the formula to get a score. If the average loss is zero, the RSI is 100.

Why Relative Strength Index Matters

Knowing the RSI helps you see the strength of a current price trend. It can alert you to potential reversals before they happen. This number helps you make safer choices about when to buy or sell.

Why Momentum Is Important for Trading

Momentum tells you how fast prices are moving. If you ignore momentum, you might buy just before the price drops or sell right before it goes up. Watching the RSI helps you avoid making a trade at the wrong time. It suggests when a price move might be running out of energy.

For Short-Term Trading

Short-term traders look for extreme RSI values to find quick turns. They may consider selling when the RSI is very high. They may think about buying when the RSI is very low. This helps them catch small price changes for profit.

For Long-Term Investing

Long-term investors use RSI to spot major shifts in market mood. A very high or low RSI might suggest a trend is getting too strong. This can help investors decide if they should hold their position or take some money off the table.

Calculation logic verified using publicly available standards.

View our Accuracy & Reliability Framework →