The expected move is the price range the options market implies for a stock over a given period, derived from implied volatility or from the price of the at-the-money straddle. It is a statistical estimate, roughly a one-standard-deviation band, not a forecast of direction or a limit on how far the stock can go.
How it works
From implied volatility
Implied volatility is quoted as an annualized standard deviation. Scaling it to the period gives the one-standard-deviation move:
expected move ≈ price × IV × √(days to expiry ÷ 365)
Calendar days over 365 is the common convention; some traders use trading days over 252 instead, which gives similar results. Under a normal approximation, the stock finishes within this band about 68% of the time, and outside it about 32% of the time. Because the move scales with the square root of time, quadrupling the period only doubles the expected move.
From the straddle
An at-the-money straddle is a call plus a put at the strike nearest the current price. Its price is what the market charges for exposure to a move in either direction, so traders often quote it directly as the expected move. The two methods are related but not identical: for a normal distribution, the average absolute move is about 0.8 of one standard deviation, so
at-the-money straddle ≈ 0.8 × price × IV × √(days ÷ 365)
The straddle therefore approximates the average size of the move, while the IV formula gives a one-standard-deviation band. Some traders divide the straddle by 0.8 to convert it into a one-standard-deviation figure. Either way, it pays to know which definition a source uses.
How to read it
- As a range, not a target. The expected move gives as much weight to a rise as to a fall.
- Against history. Comparing the move priced in for earnings with the stock's past earnings reactions shows whether options look rich or cheap for the event (see IV crush).
- For strike selection. Option sellers often place short strikes at or beyond the expected move, as in an iron condor; strikes inside it can be reached by an ordinary move.
- For risk sizing. A ±8% expected move over a month is a reminder that a stop 2% away sits well inside the range options treat as normal.
- Across expiries. An expiry that contains earnings or a scheduled decision carries a larger move than its neighbors, which shows how much the event itself is priced at.
Worked example (illustrative numbers)
A stock trades at $100, and its 30-day at-the-money implied volatility is 30%.
| Measure | Calculation | Result |
|---|---|---|
| 30-day expected move (1 standard deviation) | 100 × 0.30 × √(30 ÷ 365) | ≈ ±$8.60, a range of about $91.40 to $108.60 |
| 30-day at-the-money straddle | ≈ 0.8 × $8.60 | ≈ $6.90 |
| 7-day expected move | 100 × 0.30 × √(7 ÷ 365) | ≈ ±$4.15 |
Even though the week is less than a quarter of the month, its expected move is about half the monthly figure, because of the square-root scaling. In the model, roughly one month in three would end outside the $91.40 to $108.60 range.
Limitations and common mistakes
- Real returns have fat tails. Large moves happen more often than a normal distribution suggests, especially around earnings and macro events.
- Implied volatility changes. The expected move is a snapshot; it widens when IV rises and narrows when it falls.
- Quotes matter. Straddle values built from wide or delayed bid/ask quotes can be off, especially in thin options.
- Mixing definitions. Comparing a straddle-based figure with an IV-based one without adjusting overstates or understates the gap by about 20%.
- Reading direction into it. A large expected move says the market expects movement, not which way.
In Clear Tape
The free SPY, QQQ and IWM cards on the Options page show the expected move for the week, taken from the at-the-money straddle of the nearest expiry at least one day out. Pro members can analyze any stock with listed options. The Earnings panel compares the move priced in (the at-the-money straddle of the first expiry after the report) with the stock's average move over its last several reports, and labels it rich, cheap or fair once at least four past reports are available. The strategy builder shades the expected move to expiry, taken from that expiry's at-the-money straddle, on the payoff chart and measures how many expected moves away each short strike sits. All of these use the straddle definition, so they approximate the average move rather than a full standard deviation. Members see each session's closing data once the next session has opened. See pricing.
For educational purposes only. Not investment advice.