The returns from public investment, especially during periods of scaling up, are often lower than expected. To understand the mechanisms behind this regularity we exploit original information on investment projects obtained from World Bank project reports to document the extent and the drivers of time delays in project implementation. We find that almost 60 percent of investment projects are delayed by at least one year. Time overruns are common across sectors and countries. A sound planning and preparation matter for the timing of project execution. Country characteristics also play a role, as projects undertaken in countries with weaker institutions and in periods of public investment scaling up are completed with longer delays.