Abstract: The purpose of this study is to assess the effect of project scheduling on cost overruns of Nyabisindu–Nyagatovu Road Upgrading Project. Descriptive and correlational research design was employed, utilizing both quantitative and qualitative approaches to gather comprehensive data. The target population consisted of 260 professionals involved in the project, from which a sample size of 155 respondents was selected using Krejcie and Morgan sample and stratified sampling. Data collection tools included documentation, structured questionnaires and interview guides, with analysis performed using SPSS Version 29. Descriptive statistics such as means and standard deviations was calculated, while inferential analysis, including multiple regression, tested the research hypotheses. Findings showed that communication scheduling had a significant effect on cost overruns of Nyabisindu–Nyagatovu Road Upgrading Project (β = 0.257, t = 5.039, p = 0.000), resource allocation had a significant effect on cost overruns (β = 0.285, t = 5.377, p = 0.000), coordination had a significant effect on cost overruns (β = 0.136, t = 2.720, p = 0.007), and evaluation scheduling had a significant effect on cost overruns (β = 0.282, t = 4.780, p = 0.000). The study concluded that project scheduling significantly influenced cost overruns of Nyabisindu–Nyagatovu Road Upgrading Project in Gasabo District. The study recommended that the management of Nyabisindu–Nyagatovu Road Upgrading Project should strengthen communication scheduling, resource allocation, coordination, and evaluation scheduling to improve cost control and reduce unnecessary cost increases.