An advanced method for the prediction of the ultimate strength of initially deflected steel plate subjected to axial compression is introduced. In order to predict the ultimate strength performance of a plate, a new concept so called the plate index (PI) which is a function of plate slenderness ratio (β) and coefficient of initial deflection is proposed. For the definition of PI, the ultimate strength analysis by the nonlinear finite element method using ANSYS was conducted. Totally selected 100 plate scenarios were adopted based on obtained probability density of β from three representative types of commercial ships at midship section. In the case of initial imperfection, only initial deflection was considered. The ultimate strength versus plate index diagram together with proposed formula which shows high accuracy was developed. The obtained method will be useful in predicting the ultimate performance of steel plate under axial compression. © 2016 Taylor & Francis Group, London.