Construction projects are naturally tied up with contract agreement between parties involved in completing all the work that is contained in the contract. However, it is often observed that projects go beyond their allocated time due to various reasons including project uncertainties, scope changes and/or change orders. This study is therefore carried out Bahir Dar public building construction with the aim to determine a contract time procedure for public building projects, and also to investigate factors affecting contract time during construction phase. To achieve the objective of this research a desk study, survey questionnaires and case studies were carried out on selected projects. Primary data was generated from consultants and contractor organizations by using questionnaires surveys and direct interviews. Secondary data were obtained from relevant literature dealing with topics related to the study. The data was analyzed by using both descriptive and analytical statistics mainly linear regression analysis. The study revealed that some consultant organizations have standard procedure to determine contract time using empirical formula by considering project cost and factors affecting contract time. It was however found out that consultant engineers had not a clue on procedures of this empirical formula derivation, and also there is no adjustment on the project cost in case of currency inflation and this leads to assert that the empirical formula applied is in short of producing realistic contract time. Analysis of linear regression model was developed to predict new productivity rate for the selected critical civil work activities by using the data obtained from contractor’s organization and case studies were done by using this modeled productivity rates, average manpower from contractor’s data and total bill of quantities from selected projects to estimate the duration of each critical activities. Then the duration is entered to Microsoft project, which schedules the project to determine contract time in working days. Based on the findings, it can be concluded that realistic contract time are not drawn from the practices and ways that are used to determine contract time. It is therefore recommended that clients and respective consultants of a building projects have to give a realistic and reasonable contract time for the contractors, and consultant organizations have to use updated production rates for contract time determination systems.