What Is Historical Volatility vs Implied Volatility?
Historical volatility (HV) and implied volatility (IV) are two fundamental measures used by options traders to assess market risk and price options. Historical volatility, also known as realized volatility or statistical volatility, measures how much a stock's price has actually moved over a past period. It is calculated from the standard deviation of logarithmic daily returns, then annualized by multiplying by the square root of 252 (the number of trading days in a year).
Implied volatility, on the other hand, is forward-looking. It represents the market's expectation of future price movement, derived from current options prices using models like Black-Scholes. When IV is higher than HV, the market expects more volatility ahead than what has been realized — meaning options are relatively expensive. When IV is lower than HV, options may be underpriced relative to actual market movement.
How to Use This HV vs IV Chart
- 1
Enter a Stock Ticker
Type any US stock symbol (e.g., AAPL, TSLA, SPY) to analyze its volatility profile.
- 2
Choose HV Window & Lookback
Select the rolling window for historical volatility calculation (10, 20, 30, 60, or 90 days) and the lookback period for the chart.
- 3
Analyze the Chart
The blue area shows historical volatility over time, while the red line shows the current implied volatility from ATM options. When the red line is above the blue area, options are relatively expensive.
- 4
Read the Signal
The summary cards show the IV−HV spread and a pricing signal. Positive spread means options are expensive (favor selling strategies); negative spread means options may be cheap (favor buying strategies).
Why Compare Historical Volatility and Implied Volatility?
Identify Mispriced Options
When IV significantly exceeds HV, options may be overpriced — ideal for premium-selling strategies like iron condors or credit spreads.
Time Volatility Trades
Track how the HV-IV relationship evolves to find optimal entry points for straddles, strangles, and other volatility-based strategies.
Manage Risk Better
Understanding the volatility landscape helps you size positions appropriately and avoid overpaying for protection or undercharging for risk.
How Is Historical Volatility Calculated?
Historical volatility is computed using the close-to-close method. First, daily log returns are calculated as ln(Close_t / Close_{t-1}). Then, the standard deviation of these log returns over the chosen window (e.g., 20 trading days) is computed. Finally, this daily standard deviation is annualized by multiplying by √252 and converting to a percentage. This gives you the annualized realized volatility, which can be directly compared to implied volatility quoted in options markets.
The choice of window matters: shorter windows (10-day) capture recent volatility spikes but are noisier, while longer windows (60-90 day) provide smoother readings but may lag significant regime changes. Most traders use 20-day or 30-day HV as their primary benchmark against IV.