According to the present disclosure, a method of calculating a formation time of a perimeter stain is performed by a device for calculating a formation time of a perimeter stain, and includes obtaining a captured image of an analysis target by using a camera, extracting an image of a perimeter stain included in the analysis target, by analyzing the obtained captured image, calculating a major axis length and a width of the perimeter stain, estimating a formation time of the perimeter stain by using the major axis length and the width of the perimeter stain, and outputting the image of the perimeter stain and the formation time of the perimeter stain.