According to the decision No. 812 of the Supreme Court of Iran, the calculation of damages for delay in check payment is based on the due date. However, the application of the said decision and the different views among the doctrine and the judges caused that even after the issuance of the said decision, unanimity was not established among the judicial authorities and conflicting opinions were arisen in many cases. Some of the most important hypothetical disputes are the transfer of a check after protest, the passage of a long period of time from the due date and the lack of demand by the holder (rule of action) and the inclusion of the passage of time for commercial documents stipulated in Article 318 of the Commercial Law. The current research, by examining the view of the doctrine, international documents and especially the judicial procedure regarding the origin of the calculation of damages for the delay in check payment with a descriptive and analytical method, has reached the conclusion that the application of the decision of the Supreme Court does not lead to other legal rules such as expiration of commercial documents, failure to comply with commercial document transfer formalities or action rules to be inapplicable. Therefore, due to the special ruling, these cases are excluded from the application of the unanimous decision and the basis for calculating the damages for the delay in check payment will be generally from the date of claim.