The expected move: what the ATM straddle prices in

6 min read•Updated on 26 Oct 2026•by GeniAnalysis

What the at-the-money straddle prices in, how it becomes a range to expiry and a day's range, and why it is an implied range rather than a forecast.

Every option price carries an opinion about movement. The at-the-money straddle carries it in its plainest form: one number, in index points, that says how far the market is paying for the index to travel before expiry.

That number is often called the expected move. The name is a little misleading. It is not a prediction of where the index goes, or even a promise of how far. It is a price, and like any price it reflects what buyers and sellers agreed to pay at that moment.

Read that way, it is a useful figure. It turns implied volatility, which is abstract, into a range in points that can be laid over a chart.

What the ATM straddle is

A straddle is a call and a put at the same strike and the same expiry. The at-the-money straddle uses the strike nearest the current price of the index.

With Nifty at 24,000, the ATM straddle is the 24,000 call plus the 24,000 put. If the call trades at 185 and the put at 175, the straddle is 360 points. For one lot of 65, that is 360 × 65 = ₹23,400.

Why its price reads as a range

At expiry, the straddle is worth exactly the distance between the index and the strike, in either direction. If Nifty settles at 24,250, the call is worth 250 and the put nothing. If it settles at 23,800, the put is worth 200 and the call nothing. Direction does not matter. Only distance does.

So the price of the straddle today is the market's price for that distance. A buyer of the 360-point straddle needs Nifty to finish more than 360 points from 24,000 to get the premium back; a seller keeps something only if it finishes within 360. The breakevens are 23,640 and 24,360.

That is why the straddle is read as the implied range to expiry: spot plus or minus the straddle. It is the move the options market has priced as roughly average, given everything it knows now.

From the range to expiry to the day's range

A range to expiry is useful, but most intraday work needs a figure for one session. The usual conversion divides the straddle by the square root of the trading days left.

The square root comes from how movement adds up over time. Daily moves do not all point the same way. Some days go up, some go down, and part of each day's move cancels part of another's. If a typical day is 180 points, four such days do not add up to 720 points; they add up to something closer to 180 × √4 = 360.

As a share of the index, the range to expiry is 1.5 per cent either side, and the day's range 0.75 per cent.

An implied range, not a forecast

The straddle is not one standard deviation of the move. A common rule of thumb is that it comes to about 0.8 of a one-standard-deviation move. The reason is that the straddle prices the average size of the move, and under the usual pricing assumptions the average size of a move is about 0.8 of its standard deviation. Treat the 0.8 as an approximation; it rests on those assumptions holding.

In the example, one standard deviation to expiry would then be about 360 ÷ 0.8 = 450 points, or 23,550 to 24,450. Running that backwards gives an annualised implied volatility of roughly 15 per cent.

On the same assumptions, the index ends inside the straddle range a little under 60 per cent of the time, and inside the one-standard-deviation range about 68 per cent of the time.

Real markets do not follow the assumptions closely. Index moves have more quiet days and more sharp days than a normal curve allows. Over long stretches, index options have tended to price somewhat more movement than followed, and when the range breaks, it tends to break by more than the curve suggests. Neither pattern holds reliably in any one week.

How the straddle decays through the week

If nothing changes except time, the straddle shrinks in proportion to the square root of the days left. The table assumes Nifty stays at 24,000 and implied volatility holds steady.

Two things stand out. The straddle loses more points each day as expiry nears: 48, then 57, then 75, and the last 180 on the final session. That acceleration is the theta described in the Greeks. And the day's range stays at 180 throughout. With volatility unchanged, the market is pricing the same size of day at the end of the week as at the start. Only the number of days left has changed.

With one trading day left, the straddle and the day's range are the same number, because the square root of one is one.

A straddle that holds its price, and one that gives way

The table is the baseline. The actual straddle rarely follows it exactly, and the gap is the informative part.

Suppose that with three days left the ATM straddle still trades at 360 instead of 312. The day's range becomes 360 ÷ √3, about 208 points. The market is now pricing larger daily moves than it did a day earlier. Implied volatility has risen, or the market has added premium for something ahead.

Suppose instead it trades at 280. The day's range becomes 280 ÷ √3, about 162 points. The market is pricing calmer sessions than before, and implied volatility has eased.

One caution. The ATM strike moves with the index. If Nifty has moved from 24,000 to 24,200, today's ATM straddle is the 24,200 straddle, not yesterday's. The comparison is of the price of movement at the nearest strike, not of one contract.

What changes it

Implied volatility. The straddle is close to proportional to IV. A rise in IV from 15 to 18 per cent lifts it by about a fifth, from 360 to about 432, with the index unchanged. This is vega at work on both legs at once.

Events. Ahead of an RBI policy decision, the Union Budget, an election result or a heavyweight's earnings, the straddle carries extra premium for that one day. Dividing by the square root of days spreads that premium evenly across the week. The result overstates the range for the ordinary days and understates it for the event day itself. Once the event passes, the extra premium usually comes out quickly.

Expiry day. On the last session the remaining time is measured in hours, and the straddle can lose much of its value in the final part of the day. Gamma is at its highest, so small moves in the index swing the straddle's value sharply. A straddle read at 10am and one read at 2pm on expiry day describe very different amounts of remaining time.

What it does not tell you

• Direction. The straddle is symmetric by construction. It says nothing about which way the index goes.
• Where the index ends. It describes a range the market has paid for, not a level it is drawn to.
• The path. Nifty can travel well outside the day's range and close back inside it. The range is about the size of the move, not the swings along the way.
• Skew. Puts at lower strikes often carry higher IV than calls at higher strikes. The ATM straddle sits at the centre and does not show that tilt; the skew article covers it.
• Whether the price is fair. A straddle can be expensive or cheap relative to the movement that follows. The number alone does not say which, and only hindsight does.

Related

• Implied volatility and skew, read off the chain
• Straddles, strangles and iron condors, in payoff terms
• The Greeks, in the order they matter
• Reading an option payoff chart
• Reading an option chain, column by column