Fertility patterns play a pivotal role in determining population growth and maternal health outcomes. Uttar Pradesh, India’s most populous state, continues to experience fertility levels exceeding the national average, with a total fertility rate (TFR) of 2.4 compared to 2.0 at the national level. The present study aims to analyze the determinants of the total number of living children among women aged 15–49 years, utilizing data from 93,124 participants in the National Family Health Survey-5 (2019–2021). A cross-sectional analytical design was applied, and associations between fertility and twelve socio-demographic factors were assessed using chi-square tests of independence. The results showed statistically significant associations between all examined variables and fertility levels (p < 0.001). Among these, age group showed the strongest association, followed by educational attainment and contraceptive use. Women residing in rural areas, with lower education, lower wealth status, and non-use of contraception, were found to have higher fertility levels. The findings underscore the critical importance of strengthening female education, expanding access to contraceptive services, and implementing targeted rural reproductive health programs. An integrated approach that simultaneously promotes education, economic empowerment, and reproductive health accessibility is essential for advancing fertility decline and supporting sustainable demographic transition in Uttar Pradesh.