How the Ex-Dividend Date Works?

What is the Ex-Div Date?

For purposes of receiving a dividend from a share of stock or a mutual fund there is only one thing you need to know:

You must buy the stock Before the Ex-Div date.

Why? Because the Ex-Div date is the day the stock begins trading 'EXcept the DIVidend'

On the ex-div date the stock virtually always opens lower by exactly the amount of the dividend.

This is because no-one who buys the stock that day can receive the dividend.

Ref: http://www.squidoo.com