Delays in projects continue to be a major threat in the construction industry, especially in developing countries where inefficiencies in planning abound. This study seeks to identify planning related determinants of construction project delays so as to come out with critical factors that influence project performance. This research adopted a quantitative methodology using a structured questionnaire survey to a number of professionals in the construction industry. A structured questionnaire survey to construction professionals in order to identify the planning-related factors of delays in construction projects so as to come out with critical factors that influence project performance using descriptive statistics and rankings to ascertain the significant factors impacting project performance. A Cochran's sample size formula was used to determine an appropriate sample size for the study.The results show that poor pre-construction planning, poor scheduling techniques, suboptimal resource allocation and poor risk assessment had the highest impact on project delays, while the pre-construction planning had a higher impact than scheduling.The study advocates the use of better planning tools, good coordination of all stakeholders, and better risk management in order to avert delays, providing critical factors impacting project performance to the professionals in the construction industry.