Historical Volatility

What Is Historical Volatility?

Historical volatility (HV) measures how much an asset’s price actually moved over a past period, calculated from daily returns and expressed as an annualized percentage. Common lookback periods are 10, 20, 30, 60, and 90 days.

Unlike implied volatility, which reflects forward-looking expectations, HV is backward-looking — it describes what happened, not what the market expects. A stock with 20-day HV of 25% moved roughly 25% annualized over the past 20 sessions.

HV is also called realized volatility. In most contexts, the terms are interchangeable: both describe actual past price movement versus the expected volatility priced into options.

Why It Matters for Options Traders

HV provides a benchmark for judging whether options are cheap or expensive. Options pricing reflects expected future volatility. Comparing that expectation to actual past movement reveals pricing context.

When IV significantly exceeds HV, options price in more movement than the asset has recently delivered. This often signals opportunity for premium sellers — if realized volatility matches historical norms, options decay favorably. When IV is below HV, options appear cheap relative to actual behavior — a potential signal for buyers.

The relationship isn’t deterministic. An asset may have low HV precisely because it’s been calm before a known catalyst. Elevated IV can be justified. Context matters: HV describes the past, which isn’t always a reliable guide to near-term behavior.

For systematic premium sellers, tracking the IV-HV spread is core to building edge. When selling strategies consistently capture premium above realized volatility, that spread becomes structural advantage — but it requires monitoring HV across multiple lookback windows, not just the most recent period.

Key Characteristics

• Backward-looking: HV measures actual past price movement, not market expectations of future movement.
• Annualized by convention: Raw daily movement is scaled up to a yearly figure for consistent comparison across assets and time frames.
• Multiple lookback windows: 10-day, 20-day, and 30-day HV each capture different aspects of recent behavior; none is definitively correct.
• IV vs. HV comparison: When IV exceeds HV by a meaningful margin, options sellers may have a statistical edge; when IV is below HV, options may be underpriced.
• Volatility clustering: Periods of high volatility tend to cluster together; low-volatility regimes also persist. HV reflects the current regime.
• Not predictive alone: Historical volatility describes what happened — future realized volatility can diverge significantly, especially around catalysts.