Free calculators by Spoke. Get a daily AI brief on every open wheel position with the iOS app.

Assignment Probability Calculator

How likely is this short put or call to get assigned? Give it stock price, strike, expiration, and IV. It returns the Black-Scholes probability the option finishes in the money, plus the probability it touches your strike at any point before expiration. Wheel traders usually care more about the second number.

Trade inputs

Option sideProbability the stock closes below your strike.

Current stock price

Strike price

Expiration30 days to expiration.

Implied volatility (%)Pull from your broker's option chain. Annualized.

Risk-free rate (%)Approximately the 3-month T-bill yield.

Probability of assignment

P(finishes in the money at expiration)

37.5%

P(touches strike before expiration, approx.)

75.0%

Wheel traders often care more about the touch probability than the ITM probability. You're rolling or taking defensive action well before expiration once the stock trades through your strike.

Quick delta shortcut

Option delta from your brokerEnter as a decimal (0.30) or a whole number (30). Sign is ignored.

|Δ| is a widely-used shorthand for the probability of ending ITM. It differs from the Black-Scholes number above by the drift term and rounding, but is usually within a few percentage points.

Two short paragraphs. Educational, not advice. Powered by the same AI behind Spoke's iOS app.

Educational tool. Not investment advice. IV is the biggest lever: a few points either way can move the assignment probability by several points. Black-Scholes is European-style and doesn't model early assignment (dividends, deep-ITM calls the day before ex-div), so real-world risk is a bit higher than what you'll see here.