When does early assignment become economically rational?
Early assignment of a short call is rational only when the dividend the holder would receive by exercising exceeds the remaining extrinsic value of the option; early assignment of a short put is rational when interest income on the proceeds exceeds the remaining extrinsic value.
Formula
incentive = dividend per share − remaining extrinsic valueShort put:
incentive = interest income on strike × remaining-life days − remaining extrinsic valueWorked example
XYZ pays a $1.50 dividend and goes ex-dividend tomorrow. A short call with remaining extrinsic value of $0.40 has an early-assignment incentive of $1.50 − $0.40 = $1.10 per share. The call holder is likely to exercise the night before ex-dividend to capture the dividend.
Common misinterpretation
Assuming that all in-the-money options will be exercised before expiration. Most are not. Early exercise destroys the extrinsic value the holder is forgoing; only when an offsetting income (dividend, interest) exceeds the extrinsic value does early exercise become rational.
Limitations
- Assumes a rational option holder. In practice, retail holders sometimes exercise irrationally.
- Does not model tax-driven early exercise (year-end harvesting).
- For deep-ITM puts in high-rate environments, the threshold becomes very small — treat any deep-ITM short put as high early-exercise risk.
Tools that use this metric
Primary references
- OCC — "By-Laws and Rules"
- Hull, J. (2017). "Options, Futures, and Other Derivatives" — Chapter on early exercise.
References cite the source institution where the underlying definition or rule is published. OptionIncomeTools does not redefine standardized options terms; it ranks and presents data using widely accepted definitions.
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Educational only — not investment advice. See the disclaimer and methodology. Material methodology corrections are logged at corrections.