An option exercisable any time before expiration. Most single-stock options are American.
What this style is
American Style (American Style) allows exercise at any moment until expiration, not only on the last day. Nearly all options on individual US stocks use this style. The name is historical geography, not a description of the market.
When early exercise actually happens
Rarely, and with strict logic: just before cash dividends that a deep in-the-money call holder exercises to capture, or in very deep puts where the cash from exercising now outweighs their thin time value. Outside those two cases, selling the contract is almost always better than exercising it. Exercise burns the remaining time value.
What it means for an option seller
The risk of early assignment lasts for the whole life of the contract, not only on expiration night. A covered call seller can have shares called away before dividends, and a put seller can be handed the shares early. The dividend calendar is part of every seller's toolkit.
Hypothetical example
A cash dividend of $1.20 tomorrow, and a deep in-the-money call with $0.30 of time value left: its sensible holder exercises today and collects the dividend instead of the thin time value. The seller of that covered call wakes up with no shares and no dividend.
Common mistake
Exercising out of enthusiasm because the contract is in the money: selling in the market gives you the immediate value and the time value together, while exercising gives you only the first. The two exceptions above are calculated, not emotional.
What it means in practice for the seller
American style means assignment can happen on any day, not only at expiration. A covered call seller can wake up to find the shares gone the evening before a cash dividend. This is why professionals running complex structures prefer European-style index options, which close that door.
Where to see it on the platform
The options chain for all the stocks we cover is American style, and the lesson pages explain early exercise step by step.
The specs of each chain show its style, and the lesson pages detail how the difference affects structures.
