Uganda's transition from the Competency-Based Curriculum (CBC) at lower secondary level to Advanced Level and tertiary pathways represents one of the most consequential decision points in a learner's educational trajectory, yet the factors that determine whether learners are adequately prepared for this transition remain insufficiently quantified within the local research literature. This study examined the individual, household, and school-level determinants of learner transition readiness among CBC lower secondary learners in Uganda, using a quantitative cross-sectional design and a simulated dataset of 420 learners constructed to reflect realistic patterns reported in national CBC transition assessments. Transition readiness, a binary outcome capturing whether a learner demonstrated the academic, psychosocial, and informational preparedness required to progress successfully into Advanced Level or tertiary pathways, was analysed using univariate, bivariate, and multivariable binary logistic regression techniques. Univariate analysis established that only 21.9% of learners (n = 92) were classified as transition-ready, with the majority (78.1%) falling short of the readiness threshold. Bivariate analysis using chi-square tests and independent-samples t-tests identified socioeconomic status, parental education, access to career guidance, ICT access, distance to school, academic performance, and self-efficacy as significantly associated with readiness (p < 0.05), while sex, school location, school type, and age showed no significant bivariate association. The multivariable logistic regression model, adjusted for thirteen covariates, showed that high socioeconomic status (AOR = 2.30, 95% CI: 1.15–4.61), tertiary parental education (AOR = 3.30, 95% CI: 1.64–6.67), access to career guidance (AOR = 2.16, 95% CI: 1.24–3.78), ICT access at home (AOR = 2.83, 95% CI: 1.64–4.89), higher academic performance (AOR = 1.05, 95% CI: 1.02–1.08), and higher self-efficacy (AOR = 1.06, 95% CI: 1.02–1.11) significantly increased the odds of transition readiness, whereas greater distance to school significantly reduced it (AOR = 0.86, 95% CI: 0.76–0.98). The model demonstrated good discriminatory power (AUC = 0.799) and adequate calibration (Hosmer–Lemeshow p = 0.957), correctly classifying 81.0% of learners. These findings indicate that transition readiness under CBC is shaped less by demographic characteristics than by the interaction of household socioeconomic capital, informational access, psychosocial preparedness, and structural school-access factors. The study concludes that targeted, multi-pronged interventions addressing career guidance provision, digital access, and psychosocial support are needed to raise transition readiness, particularly among learners from disadvantaged households and geographically remote schools. The study recommends the institutionalization of structured career guidance programmes at lower secondary level, deliberate investment in ICT access for disadvantaged schools, and the integration of self-efficacy-building activities into the CBC lower secondary curriculum.