What does beta measure?

Beta measures a stock's systematic (market) risk — how much the stock's return tends to move for each 1% move in the market. Beta = 1 means the stock moves with the market. Beta > 1 means it amplifies market moves (higher risk, higher expected return). Beta < 1 means it is less sensitive. Beta < 0 means it tends to move opposite the market.

How is beta calculated?

Beta = Cov(Rs, Rm) / Var(Rm), where Rs is the stock return series, Rm is the market return series, Cov is the population covariance, and Var is the population variance. You need at least 3 paired observations; 12–60 monthly observations is the common standard in practice.

What return period should I use?

Monthly returns over 3–5 years (36–60 data points) are the most common choice for stock beta estimation. Weekly returns increase noise; daily returns can be affected by non-synchronous trading. Use consistent periods across both the stock and the index.

What market index should I use as the benchmark?

Use the index most relevant to the stock. For US equities the S&P 500 is standard. For international stocks, use the relevant local or global index (MSCI World, FTSE 100, etc.). The choice of benchmark changes the beta value.

Is a higher beta always bad?

Not necessarily. High-beta stocks offer higher expected returns as compensation for higher risk. Whether a high-beta stock is appropriate depends on your portfolio context and risk tolerance. In a well-diversified portfolio, only systematic (market) risk is priced — unsystematic risk is diversified away.

How many data points do I need?

You need at least 3 pairs for the math to work, but the estimate will be unreliable. 12 months is a practical minimum for a usable beta. 36–60 monthly observations gives a more stable estimate. More data reduces estimation error but may include periods where the company's business fundamentals changed significantly.

Beta Coefficient Calculator

Name: Beta Coefficient Calculator
Availability: InStock
Author: Nham Vu

Enter paired stock and market returns to compute the beta coefficient — a measure of how much the stock moves relative to the overall market.

Return Data

Paste return data (CSV or table)

One pair per line: stock_return, market_return. Values in % (e.g. 2.5 for 2.5%). Header row is optional.

Beta Coefficient (β)

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Enter data and click Calculate

Data Points (n)

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Covariance (Stock, Market)

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Market Variance

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Correlation (r)

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Summary

Enter paired stock and market returns to compute the beta coefficient — a measure of how much the stock moves relative to the overall market.

How it works

Enter at least 3 pairs of stock and market returns (e.g. monthly or weekly percentage returns).
Click "Calculate Beta" to run the computation.
The tool computes the mean return for both the stock and the market.
Covariance of stock vs. market returns and variance of market returns are derived from the data pairs.
Beta = Cov(stock, market) / Var(market) is displayed along with a risk interpretation.
Use the result in CAPM or portfolio analysis to understand the stock's systematic risk.

Use cases

Estimate a stock's sensitivity to broad market movements before adding it to a portfolio.
Feed the computed beta directly into a CAPM expected-return calculation.
Compare beta across multiple stocks to rank relative systematic risk.
Academic coursework: CFA, MBA finance, and quantitative investment courses.
Validate a broker-reported beta using your own historical return data.
Stress-test portfolio beta by combining individual stock betas weighted by allocation.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu