Beta and systematic risk
When markets fall together, assets respond by different amounts. Beta describes co-movement with a chosen market, helping separate market exposure from asset-specific risk.
Change one assumption
How does market sensitivity change?
Isolate beta × market move; realized returns also include residuals and other factors.
Current market-sensitivity illustration
- Beta is supplied by the slider. No historical return sample, covariance or market variance is estimated here; this calculates only the market-sensitive component.
This illustrates model sensitivity, not a return promise or investment recommendation.
What can diversification reduce?
Asset-specific risk comes from a particular business or security, such as a failed product or an issuer event. Combining assets can reduce some imperfectly synchronized fluctuations, without guaranteeing against losses.
Systematic risk comes from shared factors affecting many assets. Adding more holdings generally does not eliminate this exposure. Beta uses a chosen market to describe linear sensitivity, rather than every possible common risk.
Read beta's size and sign
Beta = 1 indicates market-like linear sensitivity; above 1 indicates stronger sensitivity; between 0 and 1 indicates weaker sensitivity in the same direction. A 2% market move and beta 1.5 give a 3% market-sensitivity illustration, not a complete return forecast.
Beta = 0 indicates zero linear market sensitivity, while negative beta indicates opposite sensitivity in the model. Intercepts, residuals, and other factors still affect realized returns, so individual moves need not match the beta multiple.
Historical estimates depend on measurement
Choose a market benchmark suited to the investment universe, then align daily, weekly, or monthly returns and sample dates. Do not casually mix price returns with dividend-inclusive total returns. Frequency, window, and benchmark choices can all change beta.
The financial calculator's STAT linear regression helps explain slopes and scatter. An ordinary-return regression intercept is not Jensen alpha. Historical Jensen alpha estimation regresses asset excess returns on market excess returns with an explicit risk-free rate.
How does beta enter CAPM?
CAPM adds the risk-free rate to beta times the market risk premium to obtain a model-required return. With a 3% risk-free rate, 9% required market return, and beta 1.5, that return is 12%: compensation under the model's assumptions.
Comparing that required return with a realized return leads to Jensen alpha. Combining assets also requires weights, volatility, and correlation. Beta alone cannot replace a full portfolio risk analysis.
Show formal definition and formula
Historical beta = Cov(Ri, Rm) / Var(Rm). Asset and market returns must share dates, frequency, and return conventions, and market variance must be positive. Beta is an estimate, not a permanent property.
- Ri / Rm
- Same-period individual asset / specified market returns.
- Cov(Ri, Rm)
- Covariance of asset and market returns, measuring co-movement.
- Var(Rm)
- Variance of market returns; must be positive.
A common misconception
A low beta does not imply low total risk or high quality. Zero beta means little linear market sensitivity in the sample; credit, liquidity, event, and other risks can remain. Negative beta is no promise of capital protection.
Frequently asked questions
Can beta change?
Yes. Operations, leverage, and market relationships can change, as can the benchmark, sampling frequency, and estimation window. Report the method and period alongside the estimate.
Does negative beta guarantee gains in a falling market?
No. It describes an opposite linear relationship in a specified sample or model. Other factors and estimation error can dominate realized returns.