A day count convention that is used to determine the total number of days needed to calculate the interest accrued on corporate and municipal bonds (in the United States). This method centers on the assumption of a 30-day month and a 360-day year. For example, the total number of days between the two coupon days March 1 and September 1 is 180. The interest earned on a corporate bond between March and August 10 (the total number of days is 159), assuming a coupon of USD 6, would be:

159/180 x 6 = 5.3