1. A method for capacity of IT system resources including monitoring over time a signal representing a capacity of an IT system resource, collecting a dataset of said signal, analyzing said dataset based on a prediction method to forecast a behavior of said dataset, and upgrading said capacity at time t−n including allocating additional resource to the IT system, when said behavior shows that at time t said resource reaches a threshold, the prediction method comprising: performing an automatic execution of a Box and Jenkins method for forecasting the behavior of said dataset including. (a) pre-processing the dataset, including providing one or more missing values to the dataset, removing level discontinuities and outliers, and removing one or more last samples from the dataset, (b) obtaining a trend of the pre-processed dataset including identifying and filtering the trend out of the dataset based on a coefficient of determination methodology, (c) detecting seasonality to obtain a resulting stationary series including computing an auto correlation function of the dataset, repeating the detecting step on an aggregate series of a previous dataset, and removing detected seasonality based on a seasonal differencing process, (d) modeling the resulting stationary series under an autoregressive-moving-average (ARMA) model, wherein said prediction method to forecast said behavior at time t is computed based on execution of steps (b)-(d) in reverse order.