A method and system optimally determines a desired Height of Burst (HOB) over a target based solely upon the time at which the projectile reached or passes through the apogee or apex of its trajectory (t.sub.a). There are several modes of implementation. According to one mode, the downleg is determined as a percentage of the upleg. According to another mode, the time to Height Of Burst (t.sub.HOB) is calculated algebraically based substantially solely upon the time to height of apogee t.sub.a.