Trying to predict the future – resource planning and allocation in CMS

In the large LHC experiments the majority of computing resources are provided by the participating countries. These resource pledges account for more than three quarters of the total available computing. The experiments are asked to give indications of their requests three years in advance and to evolve these as the details and constraints become clearer. In this paper we will discuss the resource planning techniques used in CMS to predict the computing resources several years in advance. We will discuss how we attempt to implement the activities of the computing model in spread-sheets and formulas to calculate the needs. We will talk about how those needs are reflected in the 2012 running and how the planned long shutdown of the LHC in 2013 and 2014 impacts the planning process and the outcome. In the end we will speculate on the computing needs in the second major run of LHC.