The simple but imprecise way to calculate semi-annual bond yields
To get an initial approximation of a semi-annual bond yield, one simple method is simply to take the coupon rate on the bond to calculate the semi-annual bond payment and then divide it by the current price of the bond to get a yield. Coupon rates are quoted in terms of annual interest payments, so you'll need to divide the rate by two in order to figure out the semi-annual payment.
For instance, say you own a bond with a par value of $1,000 whose current price is $900. Its coupon rate is 2%, and it matures five years from now. To calculate the semi-annual bond payment, take 2% of the par value of $1,000, or $20, and divide it by two. The bond, therefore, pays $10 semiannually. Divide $10 by $900, and you get a semi-annual bond yield of 1.1%.