Link the brief to a budget. To be credible, a brief needs to be linked to a budget. This should be common practice, but financial figures are often missing in the brief. And if they are there, they are not always useful because clients tend to be overly optimistic about the financial implications of their projects. It is what psychologists call optimism bias or planning fallacy. As architects are wont to complain: clients ask for a Mercedes while they can only afford a Honda.This problem can be avoided by making careful and realistic costs estimates at different stages of the briefing process. At the start of the briefing process, such estimates cannot be other than rough order of magnitude (rom) estimates with a high degree of uncertainty. As the brief becomes more detailed, estimates become more accurate, although there may still be a 10 to 50% uncertainty range, depending on the building type and the information available. To avoid the aforementioned optimism bias, it is recommended that the budget be set at the higher end of the range and that the projects financial risks be carefully scrutinized.The credibility of early cost calculations can be improved by looking closely at the underlying assumptions. Most calculations will be based on general industry figures, such as cost averages for office buildings. The skill of making good cost calculations is to know how to use these data, because they are strongly influenced by location (e.g. inner city versus suburban), building shape (e.g. low-rise versus high-rise) and the design quality (e.g. average versus high-end finishes). If comparative data are scarce, it will be beneficial to develop a reference design on which to base calculations. Careful examination of these issues is worthwhile because the early phases of the project offer the best opportunities for a client to influence the projects costs. Significant changes (e.g. in size, location or quality level) can still be made without major implications. Once the design process starts, costs become increasingly locked in and difficult to change. Last but not least, cost estimates should look not only at construction costs, but also at the occupancy costs (i.e. the costs for energy, water, cleaning and maintenance). It may seem premature to consider these costs at such an early stage, but over the lifespan of a building its occupancy costs tend to be greater than the initial investment costs. Recommendations-When proceeding from a cost estimate to a budget, be aware of the degree of uncertainty of the cost estimate (e.g. a variance of plus/minus 10% - 50% is common).-Define the projects major cost drivers and give these extra attention in the brief (project size obviously, but perhaps also specific requirements concerning indoor climate or flexibility).-Be clear about what the budget includes and what not (e.g. does it include furniture? professional fees? costs for temporary accommodation?).-Do not focus solely on construction costs, but also consider costs related to a buildings facility management (catering, cleaning, maintenance, security).-Consider making a reference design that can be used for an accurate estimate of quantities.