As systems become more complex, the costs to identify and correct requirements errors can consume large portions of project budgets. In general, there are two categories of cost associated with errors – cost of identification and cost of correction. This paper addresses an important element of the second category – the behavior of the cost of error correction as a project progresses. It is based on a study that used three approaches to determine the relative costs: the bottom-up cost method, the total cost breakdown method, and the top-down hypothetical project method. The approaches and results described in this paper presume development of a hardware/software system having project characteristics similar to those used in the development of a large, complex spacecraft, a military aircraft, or a small communications satellite. The results of the study show clearly that cost-to-fix escalates exponentially as the project progresses. If the cost of fixing a requirements error discovered during the requirements phase is defined to be 1 unit, the cost to fix that error if found during the design phase increases to 3–8 units; at the manufacturing/build phase, the cost to fix the error is 7–16 units; at the integration and test phase, the cost to fix the error becomes 21–78 units; and at the operations phase, the cost to fix the requirements error ranged from 29 units to more than 1500 units.