Rolling Beta against SPY

📈 Pine Script Showcase: Rolling Beta Against SPY

Understanding how your favorite stock or ETF moves in relation to a benchmark like the S&P 500 can offer powerful insights into risk and exposure. This script calculates and visualizes the rolling beta of any asset versus the SPY ETF (which tracks the S&P 500).

🧠 What Is Beta?
Beta measures the sensitivity of an asset's returns to movements in the broader market. A beta of:
- 1.0 means the asset moves in lockstep with SPY,
- >1.0 indicates higher volatility than the market,
- <1.0 implies lower volatility or possible defensive behavior,
- <0 suggests inverse correlation (e.g., hedging instruments).

🧮 How It Works
This script computes rolling beta over a user-defined window (default = 60 periods) using classic linear regression math:
- Calculates daily returns for both the asset and SPY.
- Computes covariance between the two return streams.
- Divides by the variance of SPY returns to get beta.

⚙️ Customization
You can adjust the window size to control the smoothing:
- Shorter windows capture recent volatility changes,
- Longer windows give more stable, long-term estimates.

📊 Visual Output
The script plots the beta series dynamically, allowing you to observe how your asset’s correlation to SPY evolves over time. This is especially useful in regime-change environments or during major macroeconomic shifts.

💡 Use Cases
- Portfolio construction: Understand how your assets co-move with the market.
- Risk management: Detect when beta spikes—potentially signaling higher market sensitivity.
- Market timing: Use beta shifts to infer changing investor sentiment or market structure.

📌 Pro Tip: Combine this rolling beta with volatility, Sharpe ratio, or correlation tracking for a more robust factor-based analysis.

Ready to add a layer of quantitative insight to your chart? Add the script to your watchlist and start analyzing your favorite tickers against SPY today!