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What Is Beta? Definition and Example

What beta measures, how to calculate your portfolio’s beta with the weighted-average method, and where the number misleads.

Reviewed by:David, Senior AnalystPublished Oct 26, 2026Updated Oct 26, 20263 min readHow we research

Key takeaways

Beta measures how much an investment has moved with the market: a beta of 1.2 means it rose or fell about 1.2% for each 1% move in the S&P 500 index.
Portfolio beta is the weighted average of each holding’s beta: multiply each beta by its weight and add them up.
In Exent’s data (60 months to Sep 30, 2026), NVIDIA’s beta was 2.21, Coca-Cola’s 0.32 and gold (GLD) 0.18.
Beta only captures market risk; a low-beta stock can still fall hard on its own news.

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In this article

What is beta?
How is beta calculated?
Example: the weighted-beta method
Why beta matters for a self-directed investor
Common mistakes

What is beta?

Beta is the sensitivity of an asset’s returns to the market’s returns, usually the S&P 500. A beta of 1 moves in line with the market, above 1 amplifies it, below 1 dampens it, and a negative beta tends to move the other way.

How is beta calculated?

Beta = covariance(asset, market) ÷ variance(market). It equals the asset’s correlation with the market times the ratio of their volatilities. The figures here use 60 monthly returns against the SPDR S&P 500 ETF (SPY).

Portfolio beta = Σ (weight × beta) across your holdings, including cash at a beta of about zero.

Example: the weighted-beta method

Holding	Weight (illustrative)	Beta	Weight × beta
Vanguard S&P 500 ETF (VOO)	40%	1.00	0.40
NVIDIA (NVDA)	20%	2.21	0.44
Schwab U.S. Dividend Equity ETF (SCHD)	20%	0.69	0.14
SPDR Gold Shares (GLD)	20%	0.18	0.04
Portfolio	100%		1.02

Even with 40% in dividend stocks and gold, a 20% position in NVDA lifts the portfolio to a market-like beta of about 1.02. Weights are illustrative; betas are Exent’s data as of Sep 30, 2026.

Why beta matters for a self-directed investor

Beta tells you how much of your result is just the market. A portfolio with a beta of 1.3 that beat the index in a rising year may simply have taken more risk; alpha is what is left after adjusting for that. A risk-matched benchmark makes that comparison fair. More in is my portfolio too risky?

Common mistakes

Treating low beta as low risk: Coca-Cola’s beta is 0.32, yet it fell 37.5% in the 2020 COVID crash.
Mixing windows: betas from 1-year daily data and 5-year monthly data can differ a lot.
Forgetting that beta changes; a stock’s beta in calm years may not hold in a crash.

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Frequently asked questions

There is no single good number. A beta near 1 tracks the market; below 1 suits investors who want smaller swings and accept lower returns in strong markets.

Yes. A negative beta means the asset has tended to rise when the market falls. Few long-only holdings have a reliably negative beta.

No. Volatility measures total swings. Beta measures only the part of those swings that moves with the market.

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Key takeaways

How Do I Know if My Portfolio Is Too Risky?