Options Probability Calculator

How It Works

The Options Probability Calculator estimates the likelihood that an option will finish in-the-money (ITM) or out-of-the-money (OTM) at expiration using statistical probability models based on implied volatility. It also projects expected price movements at one and two standard deviation ranges, helping traders understand realistic move scenarios and make more informed decisions about option entry, exit, and strike selection. This tool is designed for both quick estimates and detailed planning scenarios. Results update instantly as you adjust inputs, making it easy to compare different approaches and understand how each variable affects the outcome. For best accuracy, use precise measurements rather than rough estimates, and consider running multiple scenarios to establish a realistic range of expected results.

The Formula

Variables

• S — Current Stock Price — the market price of the underlying stock today, used as the reference point for all probability calculations
• K — Strike Price — the price at which the option can be exercised; ITM occurs when stock price exceeds this for calls (or falls below it for puts)
• σ — Implied Volatility (%) — the market's forecast of how much the stock will fluctuate before expiration, expressed as an annualized percentage; higher volatility increases probability of larger moves
• T — Time to Expiration (Days) — the number of calendar days remaining until the option expires; less time means tighter expected move ranges
• Probability ITM — The statistical likelihood (0-100%) that the option will be in-the-money at expiration, assuming the stock moves according to log-normal distribution
• Expected Move — The anticipated price range the stock could move, expressed in dollars; 1 SD captures ~68% of likely outcomes, 2 SD captures ~95% of likely outcomes

Worked Example

Let's say you're considering buying a call option on a stock currently trading at $100, with a strike price of $105, implied volatility of 25%, and 30 days until expiration. Using the calculator, you input these values and discover the probability ITM is approximately 40%, meaning there's a 40% chance the stock will rise above $105 by expiration. The expected move at 1 standard deviation is about $3.95, suggesting the stock could realistically trade between $96.05 and $103.95 (roughly 68% probability). The 2 standard deviation move is roughly $7.90, painting a wider scenario range of $92.10 to $107.90 (roughly 95% probability). This tells you that while your strike is technically out-of-the-money now, there's a meaningful chance the stock reaches it, but you'd need a move larger than the typical 1 SD expectation.

Practical Tips

• Higher implied volatility increases expected move ranges significantly, so compare the same option when IV is elevated versus depressed—a stock with 50% IV will have roughly double the expected move of the same stock at 25% IV, all else equal.
• Probability ITM is not the same as profit probability; even if a call finishes ITM, you only profit if the stock rises more than the premium you paid, so always factor in the actual option price relative to the probability calculation.
• As expiration approaches (fewer days remaining), expected move ranges shrink dramatically, so if an option shows only a 30% probability ITM with 5 days left, the probability is unlikely to improve significantly unless implied volatility suddenly spikes.
• Use the expected move ranges to set realistic stop-loss and take-profit levels; trading counter to the 2 SD move is statistically risky, as moves beyond 2 SD occur only about 5% of the time under normal market conditions.
• Compare calculated probabilities across different strike prices on the same stock and expiration—this reveals whether you're choosing a high-probability conservative strike or a lower-probability aggressive strike, helping you align the trade with your risk tolerance and account size.

Last updated: April 02, 2026 · Reviewed by the CalcSuite Editorial Team · About our methodology