Ex-dividend trading is the buying and selling of a share without the right to a dividend that has been declared but not yet paid. It begins on the ex-dividend date. Anyone buying on or after that date will not appear on the register in time for the record date, so the payment goes to the seller. Before the ex-date the share is dealt with the dividend, as described under cum-dividend trading.
Exchanges set the ex-date from the record date and the settlement cycle. With settlement one business day after the trade, as in the United States since May 2024, the ex-date is normally the record date itself; with two-day settlement it is one business day earlier. On the ex-date the share price typically opens lower by about the amount of the dividend, since new buyers will not receive it, and exchanges adjust open orders and derivatives accordingly.