Ex-dividend date
The ex-dividend date is the day from which buying a share no longer carries the right to the next dividend. To collect it you must hold the share before that date; anyone buying on it or later does not receive it. At the open of the ex-dividend session the price typically opens marked down by roughly the amount distributed, which explains falls that look abrupt on a chart and answer to no news at all. This is why adjusted historical series correct that jump: without the adjustment, any long-run return calculation comes out wrong.
How it is calculated
There is no formula, there is a calendar, and only one of its dates decides. If the ex-dividend date is 8 March and payment is on the 20th, you must own the share before the 8th to collect: someone buying on the 9th does not get that dividend even if they hold past the 20th. The record date, when the company looks at its shareholder register, coincides with the ex-dividend date in the United States since settlement moved to T+1 in May 2024, and falls one business day later in Europe, where it is still T+2. And on that day the share opens cheaper, roughly by the dividend amount: that is arithmetic, not a fall.
The figures in the example are invented and rounded so the arithmetic can be redone by hand. They are not data from any real company.
What it is NOT
It is not the payment date, which is the one most listings show first because it sounds like "when do I get paid". By the time the payment date arrives, the register closed weeks ago. And buying just before the ex-dividend date to collect and sell afterwards gives you nothing: you collect the dividend and lose practically the same in the price, with the difference that part of it has now been taxed.
See also
Explained in depth
See it on real data
Celsmar computes this from the accounts companies file with their regulator, and shows which line every figure comes from. Free to start, no card.
Definition for informational purposes. It is not financial advice nor a recommendation to buy or sell.