Adhesively bonded joints are gaining popularity among automotive industries due to their light-weight, cost-effective, and multi-material joining solutions. Adhesively bonded joints not only yield light-weighted structures but also provide a more uniform stress distribution than riveted joints resulting in higher fatigue life. However, due to their complex damage mechanism it is not easy to analytically predict the transition between crack initiation, propagation and failure of the joint. To improve the confidence of crack detection and estimation in adhesively bonded lap-joint, this paper proposes a numerical guided wave modal analysis to better understand the fatigue damage. From initial experiments it was found that the crack inside adhesive lap-joints increases at different rates depending on the state of the damage and can be modelled according to the paris-paris law. However, accurate estimation of the transition from crack initiation and crack propagation until total failure is non-trivial. In this paper, a series of finite element simulations are conducted to understand the modal behavior of guided waves at various damage states of the lap-joint and extract the most useful features indicative of transition form from crack initiation and crack propagation. Extracted features shall be used in various prognosis models to improve the remaining-useful-life prediction.