Objective <p>Root caries is a significant oral health concern among older adults, yet accessible self-assessment tools are lacking. This study aimed to identify factors associated with root caries experience and develop a web-based user-friendly tool for self-assessment.</p> Methods <p>Oral examination and questionnaire data from adults aged 65–74 were extracted from the Fourth National Oral Health Survey in Sichuan, China (<i>n</i> = 714). Factors associated with root caries experience were identified by using univariate/multivariate logistic regression models to build the Root-caries-assessment Nomogram (RAN). The model was internally validated via five-fold cross-validation and externally validated on a spatiotemporally distinct cohort from Jianyang, Sichuan in 2024 (<i>n</i> = 200). Based on the nomogram, a mobile-friendly online self-assessment tool was developed using web-based technologies.</p> Results <p>Five significant variables were included in the RAN model: annual per capita household income ≤ 10k CNY (OR 2.34, 95% CI 1.62–3.38), brushing teeth less than twice daily (1.79, 1.24–2.59), not using or being unsure about toothpaste during brushing (5.13, 2.89–9.61), self-rated oral health as average/poor (2.62, 1.81–3.82), and a low standardized Geriatric Oral Health Assessment Index score (1.45, 1.04–2.02). The model demonstrated good discrimination internally (AUC 0.73, 95% CI 0.69–0.76), which was preserved upon external validation (0.73, 0.66–0.80). An online self-assessment tool based on RAN enables older adults or caregivers to estimate the probability of root caries experience without professional clinical exams.</p> Conclusions <p>The RAN model supports accessible, community-based screening by enabling older adults and their caregivers to estimate their probability of experiencing root caries and seek timely professional evaluation, thereby helping to reduce disparities and improve the efficiency of preventive care.</p>