Key Takeaways
- A priced range, not a forecast: the expected move is the one-standard-deviation move options imply.
- The core formula: price × implied volatility × √(days ÷ 365).
- The straddle shortcut: an at-the-money straddle is worth about 0.8 of that move.
- Two numbers, one name: platforms quote different versions, so check which one you see.
- Events break the scaling: earnings pack volatility into one day, then implied volatility drops.
The expected move, sometimes called the implied move, is the price range that options prices imply a stock or index will finish inside at a given expiration, about 68% of the time. You calculate it by multiplying the stock price by its implied volatility and by the square root of the time left as a fraction of a year. A quicker shortcut is the price of the at-the-money straddle, which comes out at roughly 0.8 times the same move.
Neither number is a forecast of direction or a promise about size. It is what the options market is charging for movement, and it is useful precisely because it turns an abstract implied volatility percentage into dollars and a price range you can compare with a chart.
What the Expected Move Actually Is
A one-standard-deviation range, priced by the market. Implied volatility is quoted as an annualized standard deviation of returns. Cboe's VIX explainer gives the cleanest example: a VIX reading of 16 means that, based on S&P 500 option premiums, the index is expected to stay within a ±16% range over one year about 68% of the time, which is one standard deviation.
The same logic applies to any optionable stock. For example, if the options on a stock carry 30% implied volatility, the market is pricing an annual one-standard-deviation move of about 30% in either direction. The calculation simply rescales that annual figure to the time you actually care about, whether that is a week, a month or the next earnings report.
Two words in that definition carry most of the weight. Standard deviation is a measure of spread: under a normal distribution, about 68% of outcomes land within one standard deviation of the starting point, the convention Cboe uses when it describes the VIX, and about 95% within two. Implied means the figure is backed out of what traders are paying for options, not measured from the stock's own history, so it reflects demand for protection and speculation as well as expectations.
The concept most often confused with this priced range is the straddle price, which many platforms display under the same label. They are related but not equal, and the gap between them is covered in its own section below.
How to Calculate the Expected Move
The formula: expected move = stock price × implied volatility × √(days to expiration ÷ 365).
The square root is the important part. A Cboe Insights post on the Rule of 16 puts it directly: volatility is proportional to the square root of time, and implied volatility is expressed as an annualized number. Twice as much time does not double the expected range; it multiplies it by about 1.41.
Work it through with round numbers. Suppose XYZ trades at $100 and its options expiring in 30 days carry 30% implied volatility:
- Time factor: √(30 ÷ 365) = √0.0822 = 0.2867.
- Expected move: $100 × 0.30 × 0.2867 = $8.60.
- Expected range: $100 − $8.60 = $91.40 to $100 + $8.60 = $108.60.
Under the model, the options market in this hypothetical is pricing about a 68% chance that XYZ finishes that month between $91.40 and $108.60, and about a 32% chance it finishes outside, split between the two sides. Doubling the range to two standard deviations, $82.80 to $117.20, would cover about 95% of outcomes.
Volatility grows with the square root of time, not with time itself. Four times as long buys only twice the range.
The daily shortcut. For a one-day move, Cboe's post uses the Rule of 16: there are roughly 256 trading days in a year, and the square root of 256 is 16, so dividing annualized implied volatility by 16 gives an approximate one-day, one-standard-deviation move. For example, a stock with 32% implied volatility has a daily expected move of about 32 ÷ 16 = 2%, or ±$2 on a $100 stock.
How the Expected Move Differs From the Straddle Price
The straddle is about 80% of the expected move. An at-the-money long straddle is one call and one put at the same strike, so its price is a direct, model-free quote of what the market charges for movement. A well-known approximation published by Brenner and Subrahmanyam in 1988 shows that an at-the-money option (strictly, one struck near the forward price, with low interest rates and no dividends) is worth roughly 0.4 × price × implied volatility × √time, which puts the straddle at about 0.8 times the one-standard-deviation move.
Check it against the example. Suppose the 30-day XYZ $100 call trades at $3.45 and the $100 put at $3.40, so the straddle costs $3.45 + $3.40 = $6.85. The approximation gives 0.8 × $100 × 0.30 × 0.2867 = $6.88, nearly the same. Dividing the straddle by 0.8 recovers the full move: $6.85 ÷ 0.8 = $8.56, close to the $8.60 from the formula.
The two figures answer different questions:
- What it measures. The formula gives a one-standard-deviation range. The straddle price gives what it costs to buy movement in both directions.
- Where it comes from. The formula needs an implied volatility number, usually from your platform. The straddle comes straight from two quoted prices.
- What it means for a trade. The straddle price is also the breakeven distance for a straddle buyer at expiration. The formula's range is a probability band.
- How platforms show it. Some display the formula's value, some the straddle price, and some a fixed percentage of the straddle. All three get called "the expected move," and in the example above they would show about $8.60, $6.85 and, at 85% of the straddle, $5.82.
In practice, the difference matters most when you compare a stock's actual move with what was priced. For example, a stock that moves $7.50 on an $8.60 expected move and a $6.85 straddle finished inside the one-standard-deviation range but outside the straddle's breakeven, so whether it "beat the expected move" depends entirely on which number you started from.
Why the Expected Move Matters to Traders
It turns implied volatility into something you can see on a chart. For example, a 30% implied volatility is abstract, but the hypothetical $91.40 to $108.60 range from earlier is a pair of lines you can compare with support, resistance and recent swings. That makes it easier to judge whether options are pricing a move that looks large or small relative to how the stock has actually been trading.
It is also the standard yardstick around earnings, where the earnings expected move is the figure most traders check first. They compare the move priced into a report with the stock's history of earnings moves, and after the report they compare the actual move with what was priced. Our piece on how earnings change implied volatility covers the run-up in implied volatility before a report and why it fades afterward.
Finally, it frames the risk on both sides of a trade. A straddle buyer holding to expiration needs a move larger than the straddle price to come out ahead, while a seller profits if the move stays smaller. The priced range does not say which side is right; it tells you what the market is charging, which is the starting point for deciding whether that price looks rich or cheap.
The expected move is not where the stock is going. It is how far the options market is paying for it to go, in either direction.
Edge Cases and Gotchas
The simple formula breaks down in several specific situations:
- Events concentrate volatility. Into an earnings report, much of the implied volatility belongs to a single day. Scaling a weekly option's volatility smoothly with the square root of time misstates the move, so traders use the expiration just after the event and read its straddle directly.
- Implied volatility drops after the event. Once the news is out, the event premium largely disappears. Our explainer on volatility crush shows why a straddle can lose value even when the stock moves.
- Downside and upside are not symmetric. Out-of-the-money puts on stock indexes and most large stocks carry higher implied volatility than equally distant calls, so the market prices a greater chance of a large drop than of an equally large rally. The SKEW index measures that asymmetry for the S&P 500.
- Real returns have fat tails. The 68% and 95% figures assume a normal distribution. Real markets produce large moves more often than that model suggests, so moves beyond two standard deviations happen more often than the 5% the model implies.
- Day-count conventions differ. Using 365 calendar days or about 252 to 256 trading days changes the result only slightly, as long as the days remaining are counted the same way: calendar days over 365, or trading days over 252. That is why the Rule of 16, a trading-day shortcut, gives a slightly larger one-day move than plugging one calendar day into the 365-day formula.
FAQ
These answers cover the questions traders ask most often once they start reading expected-move figures on their platform.
What Does the Expected Move Mean?
It is the range options prices imply the underlying will finish inside at a given expiration about 68% of the time, which is one standard deviation.
The price can trade outside that range before expiration more often than that. It is not a prediction of direction, and finishes beyond it happen roughly a third of the time if prices followed the model exactly.
How Do You Calculate the Expected Move From a Straddle?
Add the prices of the at-the-money call and put for the expiration you care about. Under a standard approximation, that straddle price is roughly 0.8 times the one-standard-deviation move, so dividing it by 0.8 gives an estimate of the full one-standard-deviation range.
Is the Expected Move Accurate?
It is a price, not a measurement of what will happen. It reflects what traders are paying for options, including any premium for uncertainty, so actual moves can land well inside or well outside it. Treat it as the market's estimate of size, not a boundary.
How Do I Find the Daily Expected Move?
Divide annualized implied volatility by 16 to get an approximate one-day, one-standard-deviation move in percent. A Cboe Insights post explains this as the Rule of 16, because the square root of roughly 256 trading days in a year is 16.
Why Does My Platform's Expected Move Differ From My Calculation?
Platforms use different conventions. Some show the full one-standard-deviation move from implied volatility, some show the at-the-money straddle price, and some show a fixed percentage of the straddle. Each answers a slightly different question, so check which one your platform uses before comparing.
