Ex-Dividend Date Mechanics

A company doesn't just announce "we're paying a dividend" — it fixes four dates, and only one of them determines whether you get paid. The declaration date is when the board announces the dividend. The record date is the cutoff: whoever is the official shareholder of record on that date gets the payment. The ex-dividend date is the first trading day on which a new buyer will not be on the books in time to be the shareholder of record, because settlement takes a day or two. The payment date is when the cash actually shows up.

Because a share bought on or after the ex-dividend date carries no claim on the upcoming payment, the stock is worth exactly that much less the moment trading opens — an owner from yesterday still gets the dividend, a buyer from today does not, so the price mechanically adjusts down by roughly the dividend amount to keep both sides fair.

$$P_{\text{ex}} \approx P_{\text{cum}} - D$$

where $P_{\text{cum}}$ is the "cum-dividend" price (still carrying the right to the payment) and $D$ is the dividend per share. This is not a market crash or a sell-off — it is bookkeeping the market performs automatically at the open.

A worked example

A stock closes at $52.00 on the day before its ex-dividend date, carrying a $0.60 quarterly dividend. It opens the next morning around $51.40 — a $0.60 drop that has nothing to do with company news. An investor who bought at $52.00 the day before still receives the $0.60 payment on the payment date a few weeks later, so their combined position (stock + declared dividend) is unchanged; an investor who buys at the $51.40 open gets no dividend but paid $0.60 less for the stock.

Anyone building a historical price series has to adjust for every ex-dividend date the same way as for splits, or a chart of "returns" will show a fake loss on every dividend date that never actually happened to a holder who reinvested.