What Is a 1-Sigma Move in Options Trading?

Introduction

A 1-sigma move (one standard deviation) in options trading refers to a price change the market expects to occur within a certain timeframe roughly 68% of the time. It is derived from implied volatility and gives traders a statistical way to frame the range of probable price outcomes over a specific period.

Understanding 1-sigma moves is fundamental to options strike selection, risk assessment, and understanding what your broker means when it says "expected move."

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What Does "Sigma" Mean in Statistics?

Sigma (σ) is the symbol for standard deviation — a measure of how spread out a set of values is from their average. In a normal distribution:

• ±1 sigma covers approximately 68% of all outcomes
• ±2 sigma covers approximately 95% of all outcomes
• ±3 sigma covers approximately 99.7% of all outcomes

Options pricing uses this framework because implied volatility is, in essence, the market's collective estimate of the standard deviation of future price returns over a given period.

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How Is a 1-Sigma Move Calculated?

The formula is:

1-sigma move = Underlying price × IV × √(DTE / 365)

Where:

• Underlying price = current price
• IV = annualized implied volatility (as a decimal)
• DTE = days to expiration

Example:

• Underlying = $4,500
• IV = 18% (0.18)
• DTE = 21 days

1-sigma move = $4,500 × 0.18 × √(21/365) = $4,500 × 0.18 × 0.2397 = ~$194

This means the market expects price to stay within ±$194 of the current level (between $4,306 and $4,694) approximately 68% of the time over the next 21 days.

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How Does This Relate to Options Delta?

Delta and standard deviation are closely linked. An option with a delta of approximately 16 corresponds to a strike placed at roughly the 1-sigma level. This is because 16-delta options have roughly a 16% probability of expiring in-the-money — which matches the probability outside the 1-sigma range on each side (100% − 68% = 32%, divided by 2 = 16% per side).

This connection makes delta a convenient shorthand for standard deviation positioning. Traders who want to place short strikes at the 1-sigma level simply look for options with deltas around 16.

For a practical guide to using delta in strike selection, see best delta for iron condor short strikes.

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Why Do Options Traders Care About 1-Sigma Moves?

Strike placement. If you're selling an iron condor and you place the short strikes at the 1-sigma level, you know statistically that the market is expected to stay within your profit range about 68% of the time. Moving strikes to 2-sigma raises that to 95%.

Risk framing. When evaluating a potential options trade, knowing what constitutes a 1-sigma move helps you assess whether the short strikes are reasonable — or dangerously close to the current price.

Expected move vs. actual move. Markets routinely make moves larger than 1-sigma (especially in volatile environments). The 68% figure is a statistical expectation based on implied volatility at the time, not a guarantee. Fat tails are real, and options traders account for this.

See how to use standard deviation to set iron condor strikes for a practical application of this calculation.

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1-Sigma in Context: Normal Market vs. Elevated Volatility

The size of the 1-sigma move changes as implied volatility changes. When the VIX is at 15, the expected 30-day 1-sigma move for the S&P 500 is significantly smaller than when the VIX is at 30.

This has a direct impact on iron condor strike placement. In a high-IV environment:

• The 1-sigma range is wider
• Options are priced higher, so selling strikes at the same delta generates more credit
• More credit means the risk-reward is often more favorable

In a low-IV environment:

• The 1-sigma range is narrower
• Options are priced lower, so less credit is available
• Strikes may feel too close to current price to provide adequate margin for error

The CBOE VIX is the most commonly referenced measure of 30-day implied volatility for the S&P 500 and provides a benchmark for where the 1-sigma range stands at any given time.

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Sigma Moves and Iron Condors

When Tradematic selects iron condor strikes, it incorporates market data that goes beyond a simple standard deviation calculation. Real-time gamma levels, dealer hedging flows, and institutional hedge walls provide a structural overlay on top of the statistical probability range.

Tradematic is an automated iron condor trading platform that uses this institutional market intelligence to find zones of price stability where iron condors have the highest probability of remaining within the profit range. Accounts start at $1,000 and operate through Tradier and Tastytrade.

The platform handles the math — traders don't need to calculate sigma ranges manually. What matters is knowing what a 1-sigma move means so you can understand why strike placement is positioned where it is.

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Frequently Asked Questions

Is a 1-sigma move the same as the "expected move" shown by my broker? Yes, in most cases. When your broker shows an expected move for a given expiration, it is typically derived from the implied volatility of the at-the-money straddle and represents approximately the 1-sigma range (68% probability).

What happens if the market makes a 2-sigma or 3-sigma move? Your short strikes are breached. A 2-sigma move has roughly a 5% probability of occurring (2.5% on each side) in a given period. A 3-sigma move has roughly 0.3% probability. These tail events happen more often in real markets than the normal distribution predicts, which is why risk management and defined-risk structures matter.

Does implied volatility predict actual volatility accurately? Often, but not always. Implied volatility reflects the market's consensus estimate of future volatility, but actual realized volatility can be higher or lower. In general, the options market tends to overprice volatility slightly, which is one reason premium-selling strategies have historically had positive expectancy.

Can I use 1-sigma calculations for stocks as well as indices? Yes. The same formula applies to any underlying with a quoted implied volatility. Stock options often have higher IV than index options, resulting in wider 1-sigma ranges.

How often do 1-sigma moves actually occur? If the normal distribution perfectly described price returns, exactly 68% of trading periods would end within the 1-sigma range. In practice, markets have fat tails — extreme moves occur more frequently than the normal distribution predicts. This is why many experienced options traders use a slightly wider range than the raw 1-sigma calculation suggests.

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Conclusion

A 1-sigma move is the statistical range within which the market is expected to stay about 68% of the time, based on implied volatility. It is the foundation for understanding strike placement in iron condors, expected move calculations, and the probability math behind premium-selling strategies. Knowing where the 1-sigma range sits — and how it shifts with volatility — gives you a principled basis for evaluating any options trade.

Start your 7-day free trial and trade iron condors with systematic strike placement informed by probability and institutional market data.

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Trading involves risk and losses can occur. Past performance does not guarantee future results. Options trading is not suitable for all investors. Only allocate capital you are comfortable risking.