The application discloses a real-time calculating method and device for areas of a trajectory. The real-time calculating method collects multiple position points of a central point of a farming tool in a real-time manner according to preset sampling frequency. Furthermore, the method determines an initial position point, an inflection point and an end point and divides the working trajectory of afarm machinery into multiple enclosed polygons according to the initial position point, the inflection point, the end point and the width of the farming tool. Moreover, areas of the multiple enclosedpolygons are orderly calculated according to a grid method. In the end, the working area of the farm machinery is obtained. Compared with the prior art, the working area of the farm machinery can be calculated in a real-time manner during operation of the farm machinery.