除息日在股市指一个特定日期，如果某一上市公司宣布派发股息，在除息日之前一日持有它的股票的人士（即股东）可享有该期股息，在除息日当日或以后才买入该公司股票的人则不能享有该期股息。

许多上市公司定期或不定期向股东派发股息，由于这些公司的股东随股票交易而经常变更，因此需要定出一个登记基准日来判定可享有某期股息的股东名单及他们的持股量。股东如欲收取该期股息，必须确保他的股票在登记基准日前的截止过户日期前已办妥过户手续（即股票转名手续）。股票成交日期与交收日期通常不是同一天，如果在截止过户日期前最早的某一日买入的股票已赶不及办理过户，即是买方不能享有股息（卖方享有股息），该日即为除息日。

The ex-dividend date, also known as the reinvestment date, is an investment term involving the timing of payment of dividends on stocks of corporations, income trusts, and other financial holdings, both publicly and privately held. If a sale is before this date, the dividend belongs to the new owner; if on or after the date, the seller is entitled to the dividend.