American vs European options (exercise style)
An option's exercise style says when it can be exercised: American-style options at any time up to expiry, European-style options only at expiry. SPY, QQQ and single-stock options are American; SPX and NDX index options are European; CME lists both styles on its equity index futures options.
Senzoukria · Glossary · Updated September 2026
At a glance
- American
- Exercisable any business day up to expiry (SPY, QQQ, stocks)
- European
- Exercisable at expiry only (SPX, NDX)
- Name
- Refers to exercise rules, not to where the option trades
The two styles
The holder of an American-style option may exercise it on any business day before expiry; the holder of a European-style option may only exercise at expiry. The labels have nothing to do with geography. Because American exercise includes every European right plus more, an American option is worth at least as much as an otherwise identical European one; the difference is the early-exercise premium.
Which products use which style
For futures options the contract specification of each series states its style; quarterly, monthly and weekly series do not necessarily share one.
| Product | Style | Settlement |
|---|---|---|
| SPY, QQQ, IWM ETF options | American | Physical delivery of ETF shares |
| SPX and NDX index options | European | Cash |
| Options on E-mini index futures (CME) | American or European depending on the series | Exercise into the futures contract |
When early exercise matters
- Calls on non-dividend payers: early exercise throws away time value and is almost never optimal.
- Calls before an ex-dividend date: exercising a deep in-the-money call to capture the dividend can be optimal when the dividend exceeds the remaining time value. ETFs such as SPY pay dividends.
- Deep in-the-money puts: exercising early to receive the strike and earn interest on it can be optimal when rates are high enough.
- Short American options can therefore be assigned before expiry; European options cannot.
Pricing and data consequences
European options have closed-form prices (Black-Scholes, Black-76) and satisfy put-call parity exactly; American options need lattices or approximations and only satisfy parity bounds. Implied volatilities computed with a European formula on American prices carry a small bias, larger for deep in-the-money contracts. In Senzoukria's GEX module, greeks computed locally use the European Black-Scholes formula even on American ETF chains, and the Calculation assumptions panel labels that model Black-Scholes (European); for the near-the-money short-dated legs that dominate gamma exposure, the difference is usually small.
Related
In the same section
- Put-call parity
- Anchored VWAP
- AM vs PM settlement
- Arming
- Alpha decay
- At the money
- Algorithmic trading
- Auction market theory
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Frequently asked questions
- Why are SPX options European?
- They are cash-settled on an index that cannot be delivered, and European exercise removes early-assignment risk for sellers. It also makes pricing and hedging simpler, since the option can only be settled at the stated settlement value on expiry.
- Can I be assigned early on a short SPY option?
- Yes. SPY options are American-style, so a holder can exercise any business day, which results in assignment to some short position. It is most likely for deep in-the-money options with little time value, notably calls before an ex-dividend date.