In finance, a binary option is a type of option in which the payoff can take only two possible outcomes, either some fixed monetary amount (or a precise predefined quantity or units of some asset) or nothing at all (in contrast to ordinary financial options that typically have a continuous spectrum of payoff). The two main types of binary options are the cash-or-nothing binary option and the asset-or-nothing binary option. The cash-or-nothing binary option pays some fixed amount of cash if the option expires in-the-money while the asset-or-nothing pays the value of the underlying security. They are also called all-or-nothing options, digital options (more common in forex/interest rate markets), and fixed return options (FROs) (on the American Stock Exchange).

For example, a purchase is made of a binary cash-or-nothing call option on XYZ Corp's stock struck at $100 with a binary payoff of $1,000. Then, if at the future maturity date, often referred to as an expiry date, the stock is trading at above $100, $1,000 is received. If the stock is trading below $100, no money is received. And if the stock is trading at $100, the money is returned to the purchaser.

The value of a digital option can be expressed in terms of the probability of exceeding a certain value, that is, the cumulative distribution function, which in the Black-Scholes equation is the Gaussian. Due to the difficulty for market-makers to hedge binary options that are near the strike price around expiry, these are much less liquid than vanilla options. Dealers often replicate them using vertical spreads, which provides a rough, inexact hedge.

Though binary options sometimes trade on regulated exchanges, they are generally unregulated, trading on the internet, and prone to fraud. The U.S. Securities and Exchange Commission (SEC) and Commodity Futures Trading Commission (CFTC) have issued a joint warning to American investors regarding unregulated binary options.

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