Calculations are an important part of planning around a construction project. From concept to completion of the project calculation is a tool to try to predict the actual cost. During the production stage in particular, deviations occur which makes the actual cost different from the calculations.This thesis is done in collaboration with JM Residential Stockholm. The study includes a cost follow-up in which a comparison was made between the calculated production cost and actual cost for the five projects. The aim of the study was to observe the most common reasons that a project deviates from the calculated production cost and then summing these causes in a number of categories. The survey covers a limited number of accounts for each project. Information on deviations has been retrieved from cross-checking with calculations, and from interviews with those responsible for each project. The work also explains how the process of calculation is done, from early planning through to production.