Beta
How many percent this stock moves on average when the market moves 1% — it measures the degree of moving with the market, not the size of risk.
In plain terms
Beta shows "when the market (e.g. the S&P 500) rises or falls 1%, how many percent does this stock move on average." A beta of 1.5 moves 1.5 times the market; 0.5 moves about half as calmly.
One crucial point: what beta measures is not "risk" but "how much it moves with the market." Many mistake beta for the size of risk, but it is really closer to gauging "will adding this stock make my whole portfolio swing more or less."
What it tells you
Beta shows how much this stock sways with the big wave of the market. So when holding several stocks together, it is a reference for tuning whether the whole portfolio's swings get bigger or smaller.
Put the other way, beta does not capture at all the risk specific to that company regardless of the market (bankruptcy, lawsuits, accounting fraud, product failure). What beta tells you is only "the relationship with the market," not "is this company safe."
Formula
beta 1 = moves the same amount as the market greater than 1 = moves more than the market, less than 1 = less than the market, below 0 (negative) = moves opposite the market (usually computed by comparing several years of price against the market index)
What high or low means
A beta above 1 is a stock that swings more than the market (aggressive); below 1, one that swings less (defensive). Negative means it moves opposite the market.
⚠ There is a counterintuitive point. A low beta does not mean "safe." A company slowly declining regardless of the market can also show a low beta. It simply does not move with the market — the company itself may be collapsing.
Beta is computed from several years of past prices, so for a company whose business changed greatly, the old character can linger and not fit. Change the period or benchmark index used, and the value changes too.
Beta fits well in calm markets but easily breaks in a big crash. When a crisis hits, even stocks that usually moved independently fall together at once, so the hope of "low beta, so it must be safe" often collapses.
Beta measures volatility, not the possibility of loss itself. A good company can have a high beta, and beta is unrelated to a company's value, so it should be kept separate from value judgment.
During the 2008 financial crisis and the 2020 COVID crash, assets and low-beta stocks that usually moved differently collapsed nearly all at once. It plainly showed that in a crisis most stocks move in one direction together.
A portfolio that, trusting its usual beta, believed it was "well diversified" fell together at the very moment it was needed most. The lesson: beta measures the character of a calm market and is the least trustworthy indicator at the moment fear takes over.
Metrics to read alongside
See it in real stocks
Search US stocks on Stocklore to see Beta and other financial metrics alongside the sector average.
This explanation is for information and reference only and is not a recommendation to buy or sell any security. Investment decisions and their consequences are your own.