Historical vs Implied Volatility

Introduction

The word "volatility" hides two quite different ideas, and confusing them is one of the most common ways new options traders go wrong. Historical volatility looks backward: it measures how much a stock has actually moved. Implied volatility looks forward: it is the movement the market expects, baked into the price of options today. One is a fact about the past; the other is an opinion about the future.

The gap between them is where much of options trading lives. When the market expects far more movement than a stock has been delivering, its options are expensive; when it expects less, they are cheap. This lesson defines and measures both volatilities, explains the persistent gap between them — the variance risk premium — and shows how comparing the two turns "is this option dear or cheap?" from a guess into a judgement.

Quick Definition

Historical (realised) volatility is the annualised standard deviation of an underlying's past returns — what it actually did. Implied volatility is the volatility figure back-solved from current option prices — what the market expects it to do.

Historical is measured from the chart; implied is read from the options.

Historical Volatility: What Actually Happened

Historical volatility (HV), also called realised volatility, is a purely statistical measure. Take the underlying's returns over a window — say the last 30 daily closes — compute their standard deviation, and annualise it. A stock with an HV of 20% has, over that window, moved in a way consistent with a 20% annualised swing. It says nothing about the future; it is simply a description of how turbulent the past has been.

Because it is backward-looking, HV is objective but stale: a stock can be placid for months (low HV) right up until the moment it gaps on news. HV tells you the weather that was, not the storm that is coming.

Implied Volatility: What The Market Expects

Implied volatility (IV) is the opposite in spirit. It is not measured from the stock at all — it is extracted from option prices. An option's premium depends on how much movement the market expects; run that logic backward, and the premium reveals the volatility the market is pricing in. If traders expect a wild ride, they bid options up, and IV is high; if they expect calm, options are cheap, and IV is low.

Crucially, IV is forward-looking and reactive. It can rise while the stock sits perfectly still — for instance in the days before an earnings report, when everyone knows a move is coming but it has not happened yet. And it can collapse the instant the uncertainty resolves, the volatility crush that catches so many option buyers who were "right" on direction but bought when expectations — and premiums — were sky-high.

The Gap: The Variance Risk Premium

Compare the two over time and a striking pattern emerges: implied volatility usually sits above realised volatility. On average, options price in slightly more movement than stocks actually deliver.

This gap is the variance risk premium, and it exists for a sound reason. Selling options means taking on open-ended risk — the seller is the one who pays when a move blows through their strike — so sellers demand compensation for bearing it. Buyers, meanwhile, are often purchasing insurance and will pay a little over the odds for peace of mind, just as they do with home or car cover. The net effect is that option premiums are, on average, priced slightly richly relative to what the underlying goes on to do. It is not free money — a single large move can wipe out many small premiums collected — but it is a genuine, persistent tilt that disciplined sellers try to harvest.

Putting The Two Together

Comparing implied to realised turns volatility into a relative-value gauge:

• IV well above HV: the market expects far more movement than the stock has delivered. Options look rich, which can favour strategies that sell premium (credit spreads, iron condors) — accepting the move might justify the price.
• IV near or below HV: the market expects little, perhaps less than the stock has actually been doing. Options look cheap, which can favour buying premium (long options, debit spreads) — if you think a move is underpriced.

This comparison is a judgement of value, never of direction. A stock with rich IV can still crash; a stock with cheap IV can still sit still. But knowing whether you are buying or selling volatility at a good price is half of trading options well — and it is why the IV Rank and IV Percentile lesson exists, to put today's IV in the context of its own history.

Risks & Considerations

• HV is stale. A low reading reflects a calm past and can lull you right before a violent move.
• IV is an expectation, not a promise. High IV does not guarantee a big move, nor low IV a quiet one.
• The variance risk premium is an average, not a certainty. Sellers harvest small edges but can lose badly in a single event; the tilt only pays out over many disciplined trades.
• Events distort IV. Earnings and announcements inflate IV beforehand and crush it afterward — always know what is on the calendar.
• Windows matter. HV over 10 days and over 90 days can tell very different stories; choose a window that matches your horizon.

Common Misconceptions

• "High implied volatility means the stock will move a lot." It means the market expects a move and is charging for it — expectations are often wrong.
• "Historical volatility predicts future volatility." It describes the past; the future can differ sharply, especially around events.
• "If I'm right on direction, high IV doesn't matter." It matters greatly — buying when IV is inflated exposes you to the volatility crush even on a correct call.
• "The variance risk premium is guaranteed profit." It is a persistent tilt, not a certainty; one bad event can erase a long run of collected premiums.

Real-World Application

A trader is bullish on a stock the week before its earnings report. Checking volatility, they find realised volatility around 25% but implied volatility at 60% — the market is pricing in a huge move, and options are correspondingly expensive. Buying calls now would mean paying up for that inflated expectation and risking a volatility crush the moment earnings pass, even if the stock rises. Recognising the gap, they either wait until after the report, when IV has collapsed and options are cheaper, or choose a spread that partly sells the rich premium rather than buying it outright. Reading implied against realised turned an expensive, trap-laden trade into an informed choice about when and how to express the view. That is the practical power of separating what the market expects from what the stock has actually done.

Key Takeaways

• Historical (realised) volatility is backward-looking — the annualised standard deviation of past returns. Implied volatility is forward-looking — the market's expectation, back-solved from option prices.
• Implied volatility can rise while a stock is quiet (ahead of an event) and crush once the uncertainty resolves.
• Implied usually sits above realised: the variance risk premium, the compensation sellers demand and buyers pay for insurance.
• Comparing the two gauges whether premium is rich or cheap — rich IV can favour selling, cheap IV buying — but it judges value, never direction.
• Context is everything: today's IV is best read against the underlying's own history, via IV Rank and IV Percentile.