The ex-dividend date is the day on which all shares bought and sold no longer come attached with the right to be paid the most recently declared dividend. In other words, If you purchase a stock on its ex-dividend date or after, you will not receive the next dividend payment.
When a company declares a dividend, it sets a record date when you must be on the company’s books as a shareholder to receive the dividend. Once the company sets the record date, the ex-dividend date is set based on stock exchange rules. The ex-dividend date for stocks is usually set one business day before the record date.
Some investors like to wait till the last day, purchase the stock, become eligible for the dividend and then sell the stock back again. It’s a decent strategy that sometimes works and sometimes doesn’t.