The low level of public compliance in paying Motor Vehicle Tax (PKB) presents a significant challenge for local governments in optimizing Regional Own-Source Revenue (PAD). This study seeks to enhance the efficiency of the PKB due-date reminder system by implementing the Earliest Deadline First (EDF) scheduling algorithm and integrating the WooWA WhatsApp API as a medium for delivering automated notifications to taxpayers. The system was developed as a web-based application using the Waterfall methodology and tested with data from 100 vehicle license plate numbers in Ponorogo Regency. The experimental results demonstrate that the EDF algorithm effectively prioritizes message delivery in accordance with the nearest due dates. Furthermore, the use of WhatsApp through the WooWA API proved more effective than SMS, as it facilitates the transmission of more comprehensive information, offers greater flexibility, and is more likely to be read promptly by users. Overall, this system contributes to the modernization of public service delivery and fosters improved taxpayer compliance with PKB payment obligations.