Say you invest $100 in the call that expires in 30 minutes. The S&P 500 price at expiration determines whether you make or lose money. The price at expiration may be the last quoted price, or the (bid+ask)/2. Each binary options broker outlines their own expiration price rules. In this case, assume the last quote on the S&P 500 before expiration was 1,802. Therefore, you make a $70 profit (or 70% of $100) and maintain your original $100 investment. If the price finished below 1,800, you would lose your original $100 investment. If the price expires exactly on the strike price, it is common for the trader to receive her/his money back with no profit or loss, although brokers may have different rules. The profit and/or original investment is automatically added to the trader's account when the position is closed.
These are two different alternatives, traded with two different psychologies, but both can make sense as investment tools. One is more TIME centric and the other is more PRICE centric. They both work in time/price but the focus you will find from one to the other is an interesting split. Spot forex traders might overlook time as a factor in their trading which is a very very big mistake. The successful binary trader has a more balanced view of time/price, which simply makes him a more well rounded trader. Binaries by their nature force one to exit a position within a given time frame win or lose which instills a greater focus on discipline and risk management. In forex trading this lack of discipline is the #1 cause for failure to most traders as they will simply hold losing positions for longer periods of time and cut winning positions in shorter periods of time. In binary options that is not possible as time expires your trade ends win or lose. Below are some examples of how this works.
Binary options "are based on a simple 'yes' or 'no' proposition: Will an underlying asset be above a certain price at a certain time?"[20] Traders place wagers as to whether that will or will not happen. If a customer believes the price of an underlying asset will be above a certain price at a set time, the trader buys the binary option, but if he or she believes it will be below that price, they sell the option. In the U.S. exchanges, the price of a binary is always under $100.[20]