small change The Macaulay duration is one measure of the approximate change in price for a small che yield. Macaulay duration= where P-price of the bond, C-semiannual coupon interest in dollars), y one-half the yield to maturity or required yield, number of semiannual periods (number of years times 2), and M-maturity value in dollars). dP1 dy P = -modified duration modified duration= In general, the price of a bond can be computed using the following formula: . The price equation for a zero-coupon bond is: When an investor purchases a bond whose next coupon payment is due in less than six months, the accepted method for computing the price of the bond is as follows