What Is the Arms Index (TRIN), and How To Calculate It? | My Espresso

Ultimate Guide to the Arms Index (TRIN)

The arms index, also known as TRIN, is a short-term analysis and a trading indicator that compares the number of declining and advancing stocks with advancing and declining volume.

Published on 03 March 2023

The Arms Index, also known as the short-term trading (TRIN), has three readings:

  • TRIN indicator is required in finance but is often used in relation to other indices.
  • This breadth indicator was developed by Richard Warms in 1967.
  • TRIN serves to identify conditions where the market is short-term and is oversold or overbought.

TRIN meaning involves comparing all advancing and declining stock issues and trading volume as an indicator that helps judge overall market sentiment. It draws a relationship between the demand and supply of market data and helps in predicting price movement on an intraday basis.

  • Trin is calculated by dividing AD, advance-decline ratio, by the same volume ratio.
  • Trin indicator is used to gauge the overall market sentiments.

The Formula TRIN, Arms Index

TRIN= Advancing or Declining stocks / Advancing or Declining volume


  • Advancing stocks are the number of stocks that are higher on the day
  • Declining stocks are the stocks that are lower on the day
  • Advancing volume is the total volume of advancing stocks in total
  • Declining volume is the total volume of declining stocks.

Calculating TRIN or the Arms Index Formula

The arms index, known as TRIN, can be calculated using software and charting applications. However, it can be calculated by hand as well.

  • The first step is to calculate the AD ratio, i.e., advancing/declining stock at a set interval
  • Moving on, calculate the AD volume ratio
  • Now, divide the advancing, declining, AD ratio by the AD volume
  • Record the results from the above readings, plot them on the graph, and repeat the process at the next interval.
  • The last and final step is to connect multiple or all points of the data to plot on a graph and observe the movement of the TRIN over time.

What does the TRIN Reading Indicate?

  • If the advancing declining AD volume ratio creates a higher ratio than the advancing declining AD ratio, TRIN will be >1. This is considered to be bullish.
  • If the advancing declining AD volume ratio has a lower ratio than the advancing declining AD ratio, TRIN will be <1. This is considered to be bearish.
  • TRIN reading of less than 1 generally accompanies a strong price advance because the strong volume in risking stocks helps to fuel the rally
  • TRIN reading above 1 accompanies a strong price decline. This is because the strong volume in decline helps in fueling the selloff.
  • The arms index or TRIN moves to lower levels when there is a strong price rally, and a falling index will lead to TRIN pushing higher.

Note: The farther the TRIN value is from 1, the greater the contrast in force there is between buying and selling on an intraday basis.

Since daily readings are volatile, the Arms Index is displayed as a 10-day moving average on a scale.

Importance of TRIN, the Arms Index

The TRIN indicator plays a vital role in finance. TRIN is displayed on the NYSE (New York Stock Exchange) central wall during trading hours.

The Arms Index or TRIN differentiates itself from other indices by taking the volume of stocks into consideration. Various indices are available, and companies must use more than one index to provide a more in-depth and thorough analysis.

Moreover, it is vital to note that the farther the TRIN reading is from 1, the larger the contract between the buying and selling stocks. A TRIN reading exceeding 3 is indicative of an oversold market where the bearish sentiment is overheating. This might also lead to an upward reversal in prices in the future. On the other hand, a TRIN reading below 0.5 might indicate that the market is overbought.

Nevertheless, it is imperative to refer to various indices to get a better understanding and more clarity. Additionally, not only is the Arms Index reading carefully examined but the rate of change is also looked at closely and carefully to see if the market changes direction in the near future.


However, there are a few shortcomings to the Arms Index or TRIN as well. Such a system might have some errors in its analysis and hence give false readings as a result. The TRIN must be used in partnership with other indices to achieve cohesive results.

Also, the Arms Index is based on overall market performance, specifically in volume and breadth. Also, other technical parameters are to be combined with trades to get an accurate and appropriate reading. Using a TRIN or an arms index can result in inaccuracies associated with the volume of stocks taken into account while calculating the value.

Chandresh Khona
Team Espresso

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