Implied vs realized volatility: the gap that decides an options trade
Options Verdict · Updated October 18, 2026
Short answer: implied volatility is how much movement option prices assume. Realized volatility is how much the stock actually moves. If a stock moves less than implied, option sellers come out ahead on average. If it moves more, buyers do.
What implied volatility is
Implied volatility (IV) is backed out of option prices. Take an option's market price, plug everything else into a pricing model such as Black-Scholes, and solve for the volatility that makes the model match the price. It's the market's price for movement, quoted as an annual percentage. An IV of 25% means options are priced as if the stock's typical yearly move were about 25%.
What realized volatility is
Realized volatility (also called historical volatility, or HV) is measured from the stock's own price changes: the standard deviation of daily returns over a lookback such as 10, 20 or 30 trading days, scaled to a year. It describes how much the stock has actually been moving, not what anyone expects.
Put them on the same clock
IV is quoted over calendar time, including weekends. Realized volatility is measured over trading days, about 252 a year. Before comparing them for a specific trade, convert both to the trade's own horizon: IV × √(calendar days ÷ 365) and realized × √(trading days ÷ 252). Skipping this makes short-dated trades over a weekend look better or worse than they are.
Why the gap matters: one trade, five outcomes
A $100 stock with 30 days to expiration and 25% IV. The 87 / 92 / 109 / 114 iron condor collects about $66.53 per contract. Hold the price fixed and change only how much the stock really moves:
| Realized vol | Profit chance (realized) | Expected value |
|---|---|---|
| 15% | 96.6% | +$58.85 |
| 20% | 88.9% | +$34.91 |
| 25% (= implied) | 79.8% | +$0.00 |
| 30% | 71.2% | −$37.44 |
| 35% | 63.7% | −$72.85 |
Same trade, same price, opposite results. When realized volatility matches implied (25%), the expected value is close to zero, because the option prices are then exactly fair. Every dollar of edge comes from the gap.
Does implied usually run above realized?
For broad stock indexes, research has found that implied volatility has exceeded the volatility that followed more often than not. Academics call the difference the volatility (or variance) risk premium. It's why selling index options has earned money on average over long periods, with occasional large losses when markets crash and realized volatility spikes far above implied. For single stocks the premium is smaller and less reliable, especially around earnings.
The catch: realized volatility looks backward
- It's a forecast stand-in. Last month's movement is a reasonable guess for next month's, but regimes change, and the biggest losses come when they do.
- The lookback matters. A 5-day reading is noisy; a 1-year reading misses today's market. A lookback close to the trade's length is a sensible start.
- Known events. Earnings, Fed days and other scheduled news raise IV for good reason. A quiet realized volatility from before the event understates what's coming.
- Measurement error. A realized volatility measured over n days has a sampling error of about 1 ÷ √(2n): roughly 22% of its value for 10 days. A small gap between implied and realized may just be noise.
How Options Verdict uses it
The app prices options with implied volatility (and skew), and estimates outcomes with realized volatility. Expected value, profit chance and position size all come from that comparison, and every formula is shown in the app's "Check the math" sheet. It never tells you to place a trade; it shows what the numbers imply. See the full methodology.
Questions
Is high implied volatility good for option sellers?
Only relative to how much the stock actually moves. High IV on a stock that's about to move a lot (say, before earnings) can still be cheap.
What's IV rank or IV percentile?
Where today's IV sits within its own range over the past year. It says whether IV is high for that stock, not whether it's high relative to realized volatility.
Which realized volatility should I use?
One measured over a similar length to the trade. For a 30-day trade, 20- or 30-day realized volatility is a sensible start.
Try it
- Options profit calculatorPayoff, max profit and loss for 20 strategies.
- Expected value calculatorWhat a trade makes on average, from realized volatility.
- Probability of profit calculatorThe market-implied chance a trade ends with a profit.
- Position size calculatorHow many contracts fit your risk rules.
- Expected move calculatorHow far the market expects a stock to move.