How accurate is the expected move?

It is an estimate, not a boundary. Under a normal model, the close lands outside a one-standard-deviation range about 32% of the time, roughly one day in three. Real returns have more extreme days than a normal curve allows, and implied volatility can be higher or lower than the volatility that follows.

Why divide by the square root of 252?

Implied volatility is quoted as an annual figure, and a US trading year has about 252 trading days. Volatility scales with the square root of time, so dividing by the square root of 252, about 15.87, turns an annual volatility into one trading day.

How do I get a weekly expected move from the one-day range?

Under the same model, multiply the one-day move by the square root of the number of trading days. Five trading days is about 2.24 times the one-day move. Owl Mastery publishes only the one-day range.

Why does another site show a different expected move?

Methods differ. Owl Mastery uses IV30, the implied volatility of the listed expiry closest to 30 trading days out, and 252 trading days. Another site may use a different volatility, a calendar-day count such as 365, or the price of an at-the-money straddle for one expiry, so the numbers can differ.

What is the expected move? The implied one-day range

The expected move is the price range implied by option prices for a period, usually one standard deviation on either side of the current price. Owl Mastery's one-day range is spot plus or minus spot times IV30 divided by the square root of 252. IV30 is the implied volatility of the listed expiry closest to 30 trading days out. Under a normal model, the next close lands outside a one-standard-deviation range on roughly one day in three.

SPX levels for the Nov 10, 2026 close
Level	Price	From close
Call resistance (call wall) and gamma wall	8,100.00	+7.70%
HVL	7,660.00	+1.85%
1-day range high	7,592.67	+0.95%
Close	7,520.93
Put support (put wall)	7,500.00	-0.28%
1-day range low	7,449.19	-0.95%

How Owl Mastery computes the one-day range

Owl Mastery publishes the expected move as a one-day range, with a high and a low, for each stock and index with options data:

1-day range = spot ± spot × IV30 / √252

Spot is the underlying's price at the close the levels are computed from.
IV30 is the implied volatility of the listed expiry closest to 30 trading days out, the volatility that option prices imply, stated as an annual figure. It is the figure of one expiry, not an interpolation to exactly 30 days.
√252, about 15.87, converts an annual figure into one trading day, because a US trading year has about 252 trading days and volatility scales with the square root of time.

The range is computed once a day, after the US close, with the other gamma levels. The methodology page lists the formula with the rest.

A worked example

The numbers here are illustrative, not live data. Take a stock that closes at $200 with an IV30 of 25%.

One day of volatility is 25% ÷ 15.87, about 1.58%.
In dollars, that is $200 × 25% ÷ 15.87, about $3.15.
The one-day range runs from about $196.85 to about $203.15.

Because √252 is close to 16, dividing the annual implied volatility by 16 gives a quick estimate of the one-day move in percent. Here 25 ÷ 16 is about 1.56%.

What one standard deviation means

The one-day range is one standard deviation either side of spot. Under a normal model of returns:

about 68% of closes land inside the range
about 32% land outside it, roughly one day in three
about 16% land above it and 16% below it

These shares are approximate. Real daily returns have more extreme days than a normal curve allows, and a day's high or low can cross the range even when the close lands inside it. A close outside the range is not rare. It is a move larger than options priced for that day.

Implied volatility and historical volatility compared

The one-day range uses implied volatility, which looks forward. Do not confuse it with historical volatility, which looks back.

	Implied volatility (IV30)	Historical volatility (20D)
What it measures	The volatility option prices imply for the listed expiry closest to 30 trading days out	How much the price moved over the last 20 trading days
Direction in time	Forward	Backward
Comes from	Option prices	Daily closes
Owl Mastery formula	Input to the one-day range, spot ± spot × IV30 / √252	Sample standard deviation of the last 20 daily log returns, times √252 × 100
Where Owl Mastery shows it	The one-day range high and low	The Volatility (20D) signal

When implied volatility is well above historical volatility, options are pricing larger moves than the stock has made recently, and the reverse holds when it is below. The historical volatility article covers the backward-looking measure and its annualization.

How to read the one-day range

Distance from the close. Compare how far a level sits from the close with half the width of the range. A level inside the range is within reach of a one-standard-deviation day. A level outside it would take a larger move.
Context for a day's move. A close outside the previous day's range was a larger move than options priced for.
Next to the gamma levels. The HVL, call resistance and put support say where hedging flows may change. The one-day range says how far a typical day reaches. The guide to reading gamma levels puts them together.

The SPX page shows the one-day range high and low with their distance from the latest close.

Limits of the expected move

A normal model. The one-in-three figure assumes normally distributed returns. Real returns have fatter tails, so large moves happen more often than the model suggests.
One expiry spread over one day. IV30 is the implied volatility of a single expiry about 30 trading days out, so it is not a one-day figure. If earnings or another scheduled event falls on the next day, the one-day move that short-dated options price can be larger than IV30 ÷ √252 suggests. If the event is weeks away, it can be smaller.
Once a day. The range is computed after the close and stays fixed through the next session, while implied volatility changes during the day.
No direction. The range is symmetric around spot in dollars. It says how far price may move, not which way.
An approximate year. 252 is an approximate count of US trading days, and some sites use a calendar-day count instead.
A different model from the gamma levels. The range comes from implied volatility alone. The gamma levels beside it rest on a model of dealer hedging, which assumes who is long and who is short the options. Open interest does not show that, so the two answer different questions with different assumptions.