Arms Index

Also called TRIN (Short-Term TRading INdex) — a market breadth indicator that relates the ratio of advancing to declining stocks with the ratio of advancing to declining volume.

The Arms Index (TRIN) was developed by Richard Arms in 1967. It is calculated as: (Advancing Issues ÷ Declining Issues) ÷ (Advancing Volume ÷ Declining Volume). A reading of 1.0 indicates that volume is flowing evenly between advancing and declining stocks relative to the number of stocks in each group. Below 1.0 means more volume is going into advancing stocks (bullish); above 1.0 means more volume is going into declining stocks (bearish).

The Arms Index is a short-term indicator, best used on an intraday or daily basis. Extremely low readings (below 0.5) indicate frenzied buying and can signal short-term overbought conditions. Extremely high readings (above 2.0 or even 3.0+) indicate panic selling and can signal short-term oversold conditions or capitulation. Like contrarian indicators generally, extreme TRIN readings at the peak of panic often mark good short-term buying opportunities.

The Arms Index is one component in a broader toolkit of market internal indicators used by market timers and breadth analysts. It is most useful in combination with the Advance/Decline Line and McClellan Oscillator for a comprehensive picture of market breadth and sentiment. During normal, trending markets the TRIN may oscillate without generating clear signals; it is most actionable during extreme market conditions.

This definition is for informational and educational purposes only. Nothing on Finance Compass constitutes financial, investment, or trading advice. Always conduct your own research and consult a qualified professional before making financial decisions.