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What is the difference between American and European options?

An American-style option can be exercised at any time during its life; a European-style option only in a set period just before expiry 1. In the US, options on stocks and ETFs are American-style, while S&P 500 index options (SPX) are European-style 1. For a seller of American-style options, assignment can come on any day the market is open 1.

A call with a $50 strike at 30% implied volatility (made-up numbers). An American-style call could be exercised today: compare that with selling it, for any price, days left and spread.

Source: the StrikePath engine, pricing with the Black–Scholes formula 2 at 4.3% interest a year; a simulated example, not market prices. For learning; not advice.

Why exercising early rarely pays

A call on a stock that pays no dividend is worth more alive than exercised before expiry 3: exercising collects only the stock's price minus the strike and throws away the time value, which selling keeps, less the spread. Most exercises and assignments come on or near expiry 1.

When it happens

The usual exception for calls is the day before a stock goes ex-dividend, when a call holder may exercise to collect the dividend 4: a call holder who exercises becomes entitled to it 5. With a wide bid-ask spread and little time value left, exercising can also bring more than selling: move the spread up and the days down to see it.

What this shows, and what it doesn't

One call, model prices, no fees and no dividend. The formula behind the prices is for options exercised only at expiry 2.

Go further

Should I exercise my call option or sell it? →The same choice, in detail.What happens if my call expires in the money? →The automatic exercise.
Sources (5), checked 20 October 2026 and 27 October 2026
  1. FINRA, “Trading Options: Understanding Assignment” (14 December 2020). Read it (read 27 October 2026)
  2. Fischer Black and Myron Scholes, “The Pricing of Options and Corporate Liabilities”, Journal of Political Economy 81(3), 637–654, 1973. Read it (read 20 October 2026)
  3. Robert C. Merton, “Theory of Rational Option Pricing”, Bell Journal of Economics and Management Science 4(1), 141–183, 1973. Read it (read 20 October 2026)
  4. The Options Industry Council, “Covered Call (Buy/Write)”. Read it (read 27 October 2026)
  5. The Options Clearing Corporation, “Characteristics and Risks of Standardized Options” (June 2024), chapters I to III. Read it (read 20 October 2026)

Now try it on a scenario of your own

Pick where a simulated stock might be, and by when: drag one dot and see, side by side, what buying shares, one option, or a pair of options (a call or put spread) would each do. Free, no sign-up.

Check a trade before you make it →