On 5/30/12, National Grid plc (NGG) will trade ex-dividend, for its semi-annual dividend of $2.0166, payable on 8/15/12. As a percentage of NGG's recent stock price of $53.40, this dividend works out to approximately 3.78%, so look for shares of National Grid plc to trade 3.78% lower all else being equal when NGG shares open for trading on 5/30/12.