Rational design for flexible pavement uses fatigue models to determine allowed stresses and deformations in pavement structures which are compared with stresses and deformations calculated with response models.Fatigue models developed for different materials and climatic conditions produce different results.Due to this reason, fatigue models need to be calibrated for local conditions.No pavement fatigue models calibrations have been performed in Colombia.Pavement designers need to use fatigue laws developed for materials and conditions different to national ones, thus creating high uncertainty in the calculated pavement dimensions and long-term performance.The main goal of this research was to evaluate the effect of different fatigue laws used over the final dimensions and construction prime costs of flexible pavements.In order to do this, two pavement structures designed by the rational method were evaluated using the Bisar model and different fatigue laws.As a result, a large variation in costs and dimensions was found, thus confirming that the development and fatigue models calibration may result in significant savings when constructing pavements within the country.