Historical volatility (HV) measures how much a stock has actually moved in the past; implied volatility (IV) is the forward-looking estimate of how much it will move, read from current option prices. One is a fact about the past, computed from price history. The other is an expectation about the future, backed out of what people are paying for options right now. They are quoted in the same units — an annualized percentage — which is exactly why they get confused.
What is historical volatility?
Historical volatility — also called realized volatility — is a measure of how much a stock's price has actually fluctuated over some past window. It is computed as the annualized standard deviation of the stock's recent returns, typically over a trailing period such as 10, 20 or 30 trading days. A higher number means the stock has been making larger daily swings; a lower number means it has been calm. Because it is built entirely from price history, historical volatility is backward-looking — it tells you what already happened, not what comes next.
What is implied volatility?
Implied volatility is the volatility figure that is baked into current option prices. Option pricing models (such as Black–Scholes) connect an option's price to an expected level of volatility; given the price the market is actually paying, you can run the model in reverse to find the volatility that price implies. That number is the market's forward-looking estimate of how much the stock will move over the option's remaining life. Unlike historical volatility, implied volatility is not a single value for the whole stock — it varies by strike and expiration (the volatility "smile" and term structure). For more on how options translate IV into an expected dollar range, see the implied move.
Implied vs historical volatility: side by side
| Historical volatility (HV) | Implied volatility (IV) | |
|---|---|---|
| Looks | Backward — at realized moves | Forward — at expected moves |
| Source | The stock's past price returns | Current option prices |
| How it's found | Standard deviation of past returns, annualized | Backed out of an option pricing model |
| Shape | One number per window for the stock | Varies by strike & expiration |
| Changes when | The stock actually moves | Expectations or option demand change |
| Around earnings | Reacts after the move happens | Rises before the report, falls after |
Why implied volatility usually sits above historical
Across most stocks and most of the time, implied volatility tends to trade a little above recent historical volatility. The gap is commonly called the volatility risk premium: because option sellers take on the risk of a large, sudden move, options tend to be priced with a cushion over what the stock has actually been realizing. The gap is not fixed — it expands and contracts — but on average IV being modestly richer than HV is the normal state of affairs. This is a description of a well-documented market tendency, not a prediction or a recommendation.
The earnings connection: rush and crush
Earnings is where the IV-vs-HV gap becomes dramatic. In the run-up to a report, the market knows a potentially large one-day move is coming that the recent, calm price history does not reflect — so implied volatility climbs well above historical volatility. That build-up is the IV rush. Once results are out and the uncertainty is resolved, implied volatility collapses back down toward historical levels in the next session — the IV crush. So the distance between IV and HV is usually widest just before earnings and narrowest just after. Seeing them as one cycle — IV stretching away from HV and then snapping back — is the clearest way to understand option prices around a report. For the two-sided view, see IV rush vs IV crush.
IV vs HV is not the same as IV rank or IV percentile
A common mix-up: comparing implied volatility to historical volatility is a different comparison from comparing implied volatility to its own past values. IV rank and IV percentile measure where the current IV sits within its own range over (usually) the last year — they answer "is IV high or low for this stock?" Implied-vs-historical instead asks "is the market pricing in more movement than the stock has actually been delivering?" Both are useful lenses; they simply use different yardsticks.
How EarningsWatcher shows both
EarningsWatcher is built around the forward-looking side of this picture for earnings:
- The Moves Analyser puts a stock's implied move next to its history of actual earnings moves — implied expectation versus realized result, side by side.
- IV Rush Radar shows how implied volatility has historically built up into past reports, so you can see the rush relative to the stock's calmer baseline.
- The Simulator models the IV crush back toward normal levels after the print, per strike and expiration.
Frequently asked questions
What is the difference between implied and historical volatility?
Historical volatility (also called realized volatility) measures how much a stock actually moved in the past, calculated as the annualized standard deviation of its past returns over a window such as 20 or 30 days. Implied volatility is forward-looking: it is the level of volatility implied by current option prices, representing the market's estimate of how much the stock will move over the life of the option. In short, historical volatility looks backward at realized moves while implied volatility looks forward at expected moves.
Why is implied volatility usually higher than historical volatility?
On average, implied volatility tends to trade above recent historical volatility. This gap is often called the volatility risk premium: option sellers take on the risk of large moves, so options tend to be priced with a cushion above what the stock has actually realized. The gap is not constant, and it widens most ahead of known catalysts such as earnings, when a larger future move is expected than the recent past suggests.
How does implied vs historical volatility behave around earnings?
Into an earnings report, implied volatility rises well above the stock's recent historical volatility because the market is pricing in a potentially large one-day move (the IV rush). After the report, the uncertainty is resolved and implied volatility collapses back toward historical levels (the IV crush). So the gap between IV and HV tends to be widest just before earnings and narrowest just after.
Is implied volatility the same as IV rank or IV percentile?
No. Implied volatility is a single forward-looking number from option prices. IV rank and IV percentile instead compare the current implied volatility to its own range over the past year, to show whether IV is relatively high or low for that stock. Comparing implied volatility to historical (realized) volatility is a different comparison from comparing implied volatility to its own past values.
This article is educational and does not constitute financial advice. Options involve risk and are not suitable for every investor.