Introduction Out-of-hours primary care services cannot provide the same continuity and coordination of care as general practice. Thus, patients with high risk of complex care trajectories should, when possible, be treated by the general practitioner during daytime opening hours. This study aims to analyse the variation among general practices in the frequencies of daytime services for persons aged ≥75 years and how it relates to the patients' use of out-of-hours services. Methods and analysis Register-based cohort study of all Danish citizens aged ≥75 years, of whom >98% are listed with a general practice. Using Poisson regression, we will estimate each practice's excess variation in delivered daytime services compared with the expected based on the characteristics of its listed patients. Delivered daytime services will be analysed overall and separately for face-to-face, phone, email, home visit and preventive services. The association with the use of out-of-hours services will be analysed by Poisson regression. Ethics and dissemination Complying with European data protection rules, the legal services at University of Southern Denmark (Research & Innovation Organisation) approved the data processing activities regarding this project (journal number 11.593). According to section 14.2 of the Act on Research Ethics Review of Health Research Projects, because the study is based solely on register data, approval from the ethics committee and informed consent are not required. Results from the study will be disseminated as publications in peer-reviewed scientific journals and at international conferences.