What Is the Expected Move and How to Calculate It

From straddle pricing to a daily expected range — what the expected move calculation actually measures and how to use it.

The expected move is the market's best estimate of how far a stock or index will travel — in either direction — over a given time horizon. It is not a forecast from an analyst or a model; it is extracted directly from option prices. Because options are insurance contracts, their premiums reflect the uncertainty the market is willing to pay to hedge. The expected move calculation turns that premium into a concrete dollar range: "the market implies this stock moves roughly ±$8 over the next five days." Every trader using an options pricing calculator or sizing a position around earnings should understand exactly where that number comes from.

What the expected move calculation actually measures

Formally, the expected move is the one-standard-deviation range implied by options prices over a specific horizon. If a stock is at $100 and the expected move is $8, the market is pricing in roughly a 68% probability that the stock closes within $92–$108 by expiration. The remaining 32% of the distribution sits in the tails — roughly 16% above $108 and 16% below $92. It is a containment band, not a point forecast, and symmetry is baked in: the model assumes the stock is equally likely to rally or fall by that magnitude.

That 68% figure comes from the lognormal distribution that underlies standard options pricing. One standard deviation captures 68.27% of outcomes in a normal distribution, and the expected move inherits that interpretation. Understanding this framing matters because it tells you what the number is not: it is not a worst-case, it is not a 95% band, and it says nothing about direction.

Method 1 — deriving it from the ATM straddle

The fastest route to the expected move is pricing a straddle at the at-the-money strike. A straddle — long a call and a put at the same strike, same expiration — profits from a large move in either direction. At-the-money, the straddle's premium is dominated by extrinsic value and is a close proxy for the market's expected move over that period.

The relationship is approximate but well-known:

Expected Move ≈ ATM Straddle Price

Many desks apply a 0.85× correction to account for the fact that the straddle slightly overstates the one-standard-deviation move (the precise coefficient is 1/√(2π/2) ≈ 0.7979 for a half-normal, but ~0.85 is the common desk shorthand once bid-ask friction and skew are considered):

Expected Move ≈ 0.85 × ATM Straddle Price

If an ATM straddle on a $200 stock expiring in one week is quoted at $9.00, the raw straddle estimate is ±$9.00 and the adjusted estimate is ±$7.65. The fuller treatment of this approach — including how to read the straddle to back out the implied move from a straddle — covers additional edge cases around skew and early exercise.

Method 2 — the IV-based formula

The second method derives the expected move directly from implied volatility (IV). Because IV is annualized by convention, you need to scale it to your target horizon:

Expected Move = S × IV × √(T / 365)

where S is the current stock price, IV is the at-the-money implied volatility expressed as a decimal, and T is the number of calendar days to expiration.

This formula follows directly from the lognormal model: a $200 stock with 30% IV has an annualized one-standard-deviation move of $60. Over a 30-day period that scales to $200 × 0.30 × √(30/365) = $200 × 0.30 × 0.2864 ≈ $17.19. Over a single day it compresses to $200 × 0.30 × √(1/365) = $200 × 0.30 × 0.0523 ≈ $3.14.

Worked example — daily and weekly moves

Consider a stock trading at $150 with an ATM IV of 40%.

• Daily expected move: $150 × 0.40 × √(1/365) = $150 × 0.40 × 0.05236 ≈ ±$3.14
• Weekly expected move (5 trading days, use 7 calendar days): $150 × 0.40 × √(7/365) = $150 × 0.40 × 0.1385 ≈ ±$8.31
• Earnings (1-week window): If the near-term ATM straddle for the earnings expiration is priced at $11.00, the straddle method gives ±$11.00 raw or ±$9.35 adjusted — somewhat wider than the IV-based estimate because earnings IV typically spikes above the realized-volatility run-rate.

The two methods will not always agree. When the straddle and the IV formula diverge materially, it usually signals elevated skew or a term-structure kink — for example, a single expiration priced rich into an event while surrounding expirations are flat.

Using the expected move around earnings and 0-DTE

Earnings releases are the primary use case. Because a binary event is crammed into a single expiration, the at-the-money straddle for that expiration gets bid up to reflect jump risk. The expected move calculated from that straddle isolates the market's consensus for the earnings gap — stripping out the "ambient" IV that would price normal daily drift. Typical S&P 500 large-caps imply 4–8% earnings moves; beaten-down or high-growth names can imply 15–20%.

For 0-DTE options (zero days to expiration), the IV-based formula uses T = 1 but many practitioners substitute intraday time fractions (e.g., T = 0.5 for a half-day window). The straddle method is often more reliable here because IV readings can be noisy at the extremes of the term structure. A 0-DTE ATM straddle on SPY priced at $2.50 implies roughly ±$2.50 on a $560 index — about ±0.45%, consistent with a typical quiet-session realized range.

Caveats and limits of the measure

Three structural limitations are worth keeping front of mind:

• Symmetry assumption. The formula returns a symmetric range. Real distributions — especially around earnings — are skewed. A company likely to beat reports differently than one on a credit watch. Put skew can be severe while calls are comparatively cheap, but the single expected-move number obscures this asymmetry. Separate analysis of put vs. call skew is needed to read directionality.
• Lognormal tails. The 68% containment statement holds only under lognormal (or normal) return assumptions. Realized return distributions have fat tails; empirically, stocks exceed their expected move more than 32% of the time, particularly over short horizons with event risk.
• It moves with IV. The expected move is only as stable as the implied volatility feeding it. IV itself fluctuates with supply and demand for options. A straddle priced at market open may imply a meaningfully different range than the same straddle two hours later after a macro headline. Treat the number as a snapshot, not a constant.

Used correctly, the expected move is one of the most useful single numbers an options trader can extract from the market — a calibrated, forward-looking range that summarizes the collective pricing of every participant. Pair it with the options pricing calculator to stress-test specific strikes, and treat the ±1σ band as your map of where the market expects the action to stay — with the understanding that roughly one in three sessions, it won't.