How to calculate the missed opportunity in civil liability in Iranian and British law

Theory of lost opportunity that considers the future economic losses, Recoverable; Although widespread in British Law but Iranian law has not been addressed as it should be. We are faced with more challenges in assessing these damages, and no clear and precise criteria have been provided. Obviously, the existence of a vague criterion makes it difficult to argue for compensation under the rules of civil liability and has no preventive effect. Therefore, the main challenge of this article is to examine the criteria for calculating the opportunity loss in British law and to examine their applicability to Iranian law. At the end of this article it will be clear that in British law, the doctrine of lost opportunity is used as a way of calculating compensable damages in the assumption of loss. And calculate the amount of damage, using the "all or nothing" rule and the "Proportional Rule" to determine the Possibility and extent of the damages. The rule is relative to the recent approach of the British courts, which is also applicable to Iranian law when the probability of achieving the result is not weak.