Purpose: Construction projects in India continue to suffer excessive delays. This paper aims to investigate the delay causes in India by project sector (transport, power, buildings and water) and carry out a comparative study of delay causes in design build (DB) projects with that of design bid build (DBB) projects along with mitigation measures. Design/methodology/approach: A questionnaire survey was conducted among major clients, contractors and consultants in India. Importance Index was used for ranking of the delay causes. Projects were categorized based on the type, and causes of delay in each project type were identified. Projects were also categorized based on type of contract, and delay causes in DB and DBB projects were compared. Statistical analysis of responses by Cronbach’s alpha, one-way analysis of variance, Kruskal–Wallis tests was carried out with Statistical Package for Social Sciences. Semi-structured in-depth interviews were conducted with senior industry professionals to develop exhaustive mitigation measures. Findings: The research findings indicate finance-related causes as the most critical causes of delay in Indian projects. Delay in settlement of claims, contractor’s financial difficulties, delay in payment for extra work/variations by owner, late payment from contractor to subcontractor or suppliers, variation orders/changes of scope by owner during construction and changes in design by owner were the highly ranked delay causes. The research found no significant difference in the delay causes in DB and DBB projects. Originality/value: This is the first study wherein delay causes for various project types within a single country are identified. In addition, the study has identified and compared the delay causes in DB projects and DBB projects. Mitigation measures developed in this study will help professionals and project managers not just in India but other developing countries as well to alleviate delay causes and in improvement of project timelines. © 2019, Emerald Publishing Limited.