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.