What Is Standard Deviation in Stocks?
Standard deviation is a statistical measure that quantifies the amount of variation or dispersion in a set of data values. When applied to stock prices, it measures how much a stock's price deviates from its average price over a given period. A higher standard deviation indicates greater price volatility — meaning the stock's price swings more dramatically — while a lower standard deviation suggests the stock trades within a tighter range.
Price standard deviation describes dispersion in quoted price units, as used in Bollinger Bands. Return standard deviation describes variation in relative returns, as used in portfolio risk analysis. The raw price indicator is not interchangeable with return volatility in a Sharpe ratio or portfolio calculation.
How to Use This Stock Volatility Calculator
- 1
Search for a Stock
Type a stock ticker symbol (e.g., AAPL, TSLA, MSFT) in the search box. The autocomplete dropdown will help you find the correct provider-supported symbol. Confirm its exchange and currency.
- 2
Choose Period & Timeframe
Select the period length for the standard deviation calculation (10, 14, 20, 30, 50, or 100 bars) and the timeframe (daily, weekly, or monthly). Shorter periods capture recent volatility changes. These settings apply only to the price indicator; the return-volatility summary uses separate daily observations.
- 3
Analyze the Results
Review the dual chart showing the stock's price history alongside its rolling standard deviation. The summary cards display key volatility metrics including annualized volatility, daily log-return volatility, and the historical range of up to 30 daily closing prices. The range is not a forecast.
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Read the Historical Comparison
The table compares price standard deviation with the mean of all returned indicator observations: below 80%, within 80–120%, or above 120%. These descriptive bands use the complete loaded history, including observations after older rows. They are not signals that were available at each historical date.
Why Use a Stock Volatility Calculator?
Separate Two Measures
Compare return volatility only when window, sampling, and adjustment conventions match. Raw price standard deviations also depend on currency and price level and should not rank different stocks.
Spot Volatility Trends
Inspect how historical price dispersion changes as new bars enter the lookback window. A rising value does not establish the direction or timing of a future breakout.
Understand the Limits
Volatility is one input to a risk assessment. This calculator does not model portfolio correlations, liquidity, leverage, gaps, or a suitable position size.
How Is Stock Standard Deviation Calculated?
The price indicator comes from FMP’s standard-deviation endpoint for the chosen bar count and timeframe. This page displays that result without independently reproducing the provider’s denominator convention. Its summary mean, minimum, and maximum use all valid returned indicator observations. Zero is a valid standard-deviation value.
For the separate return estimate, the page calculates 100 × ln(Pt / Pt−1) from up to 31 recent daily closes and uses sample variance with n−1. Multiplying the resulting daily standard deviation by √252 is an annualization convention that assumes comparable, uncorrelated daily returns. It does not make the historical estimate a future price interval. Split-adjusted closes exclude dividend reinvestment, and missing provider sessions are not filled in. Read the observed window and count beside the result before comparing stocks.
Interpreting the Result
There is no universal safe or risky cutoff. Historical volatility changes with the sample and can miss rare events. A small recent value does not rule out a future gap; a large one does not establish an attractive opportunity. The historical closing-price range also excludes intraday extremes. Use the displayed units and window to understand what was measured rather than treating it as a trading recommendation.