What does volatility mean?
Stock prices and market indexes go up on some days and down on others. FINRA, which oversees US brokerage firms, calls this movement volatility.[S1]
FINRA puts it this way: "The more dramatic the swings, the higher the level of volatility".[S1] The word covers moves in both directions, so it says how far a price travels, not which way.
How is volatility measured?
There is no single number. Three common measures answer three different questions.
Standard deviation: how widely did this price swing? FINRA's glossary says that, mathematically, volatility is "the annualized standard deviation of returns".[S2]
Standard deviation is a statistic for how far results usually land from their average. "Annualized" means the figure is stated for a one-year period.
Beta: how did this price move compared with the market? Beta compares a stock with a benchmark index, and the index is assigned a beta of 1.[S1]
FINRA's example is a stock with a beta of 1.2. It has historically moved 120 percent for every 100 percent move in the benchmark.[S1]
FINRA also notes the limit of this measure. Beta shows how a stock moves relative to the market, not its total volatility.[S1]
A stock can swing widely and still have a low beta, if its moves do not track the market.[S1]
The VIX: how much movement do option prices imply for the whole market? Cboe, which publishes the index, says it is designed to measure the market's expectation of 30-day forward-looking volatility.[S4]
It covers the US stock market, as conveyed by S&P 500 Index option prices.[S4]
An option is a contract giving the right to buy or sell at a set price by a set date.[S2] FINRA notes that the VIX is not based on actual price moves on a given day.[S3]
Volatility worked out from option prices is called implied volatility. FINRA says it is calculated from current options prices, not from a stock's historical price changes.[S2]
Why is volatility not the same as risk?
The two are linked, but they are different ideas. FINRA connects them when it says wider swings mean higher volatility "and potential risk".[S1]
FINRA defines risk more broadly, as "the possibility that a negative financial outcome that matters to you might occur".[S5]
Volatility is a measure of movement. Risk is about a bad outcome, and price movement is only one route to one.
FINRA's list of risks shows the gap. It includes these:[S5]
- Inflation risk: returns may not keep up with the rising cost of living. FINRA says this applies even to insured products such as CDs.
- Liquidity risk: how easy or hard it is to cash out of an investment when the money is needed.
- Business risk: corporate decisions, such as expanding into a new line of business, can affect an investment.
- Concentration risk: the more money sits in one investment, the greater the risk taken.
So a calm price does not mean an absence of risk. A volatility figure also leaves out why a price moved.
Where does the word appear in company filings?
Companies use the word about their business as well as their shares.
Tesla's 10-K for fiscal 2025 says vehicle sales tend to be cyclical in many markets. It adds that this "may expose us to volatility from time to time".[S6]
That sentence is about the ups and downs of car sales, not a statistic about the stock. Reading the sentence around the word shows which meaning a filing intends.
Cityfort stock pages do not show a volatility or beta figure. They set out business risks from the filings under "What could go wrong", for example at Tesla.