The dividend yield is the ratio of a company’s total annual dividend compared to its share price.
A forward dividend yield is the percentage of a company's current stock price that it expects to pay out as dividends over a certain time period, generally 12 months.
A trailing dividend yield shows a company's actual dividend payments relative to its share price over the previous 12 months.
Dividend yield = Dividends for the primary issue excluding special dividends / Price of the primary issue
Dividend yield shows the percentage of income that comes from dividends relative to the share price. Dividend yield is commonly calculated on the basis of ordinary shares and dividends, for example it excludes the payment of special dividends.