Interest and capital yield of bonds

The yield of bills and bonds when sold before maturity can be divided into interest and capital parts. If there is an increase (decrease) in interest rates at some point before maturity, capital yield is positive (negative). If an owner holds the bills and bonds until maturity there is only interest yield; capital yield is zero. Capital yield can be realized or unrealized. Coupon accrued interest rate yield is defined only for bonds and is equal to the accrued coupon between the coupon payments. On the other hand, accrued interest rate yield is defined for both bills and bonds and is equal to the accrued difference between nominal value and purchase price of the bill or bond. Accrued interest rate yield for bills is positive; for bonds it is positive, zero or negative.