A method includes setting a target pattern to be formed on a substrate using a reticle, obtaining a first pattern using the reticle and a first illumination condition, calculating, a second illumination condition under which the target pattern is transferred onto the substrate using the reticle, and a third illumination condition under which the first pattern is transferred onto a substrate using the reticle, using mathematical models each of which defines the relationship between an illumination condition and a virtual pattern transferred onto a substrate using the illumination condition, determining a fourth illumination condition, obtained by adding the difference between the calculated second illumination condition and third illumination condition to the first illumination condition, as the illumination condition, and transferring the pattern of the reticle onto the substrate by illuminating the reticle using the determined illumination condition.