To help to plan for minimum costs during the whole life of a pavement, a computer model, of the costs of construction and of structural maintenance incurred throuhgout the life of a pavement, has been developed. In the model, pavement designs for initial construction are obtained from mathematical expressions of the design procedures given in Road Note No.29, and for overlays, the relationships between pavement pavement standard deflection and traffic given in TRRL Laboratory Report LR 833. Costs of initial construction are combined with discounted costs of subsequent overlays to give a total present value of the costs for each design being considered. In its present stage of development the model makes no estimate of the costs of traffic delay or of consequential work at the times of overlays construction, though the likely influence of these effects is discussed. Costs of constructing flexible pavements in 2,3 or 4 stages have been compared with the cost of single-stage constrcution using the resource costs from actual construction contracts. The sensitivity of the results to variation in the model parameters is examined. The results show that construction in more than two stages is rarely economical. For pavements designed to have lives of up to 20 years single-stage construction is the economical choice. For pavements designed to last between 35 and 40 years, two stage construction is cheaper than construction in one stage