A method for verifying a lithographic process is described. During the method, a set of guard bands are defined around a target pattern that is to be printed on a semiconductor die using a photo-mask in the lithographic process. An estimated pattern is calculated using a model of the lithographic process. This model of the lithographic process includes a mask pattern corresponding to the photo-mask and a model of an optical path. Then, whether or not positions of differences between the estimated pattern and the target pattern exceeded one or more guard bands in the set of guard bands is determined.