This paper explores the accuracy of cost estimates at different planning stages for Swedish transport infrastructure projects 2004-2022. Changes in project costs are tracked between the national investment plans established in 2010, 2014, 2018 and 2022. Cost estimates tend to increase considerably during the planning stages on average, while cost estimates at start of construction do not deviate systematically from final costs. The distributions of cost escalations between subsequent investment plans are highly skewed, with modes close to zero, but means in the order of 20-30 percent for projects in the planning stages. Average cost escalations are larger for rail projects than for road projects. The paper also briefly describes the Swedish infrastructure planning and decision process, summarizes previous Swedish studies, and discusses possible causes and remedies of cost overruns.