Background <p>Contraceptive service is a fundamental reproductive right for all women to safeguard the unplanned pregnancies and unsafe abortions that remain a significant public health challenge in India. Early marriage places a greater burden on sexual reproductive health for adolescent girls. This study aims to investigate the determining factors associated with Modern contraceptive use (mCPR) among adolescent and adult married women aged 15–49 years in India.</p> Methods <p>We assessed the use of mCPR and its determinants among 13,760 adolescents (15–19 years) and 5,29,070 adult married women (20–49 years) in India using the National Family Health Survey (NFHS-5) data. A multivariable binary logistic regression model was applied to identify factors associated with mCPR use.</p> Results <p>We discovered that around 13% adolescent girls in India were married in NFHS-5, and only 18% respondents from this category use modern contraceptives. Therefore, most respondents were not using the method. Traditional contraceptive use has increased over time in both groups. Male condom and periodic abstinence are the most famous contraception in the adolescent group here. The results also revealed that an overall 38.17% gap in mCPR usage was found between adolescents and adult married women. The adolescent women with higher educational attainment, wealthier households, having more children, and media exposure and services talked regarding family planning in the last 3 months were more likely to use mCPR significantly. On the contrary, married adults who lived in urban areas, have higher educational attainment, belonged to general caste, and the Muslim religion was found to be associated with lower mCPR usage.</p> Conclusion <p>The mCPR use among married adolescent girls in India remains substantially lower than among married adult women, with a wide and persistent gap in mCPR despite overall increases in contraceptive use. The findings reveal the impact of household wealth, social groups, exposure to mass media, and recent contact with family planning services. Among adolescents, higher education, greater wealth, parity, media exposure, and recent family planning discussions were found to be associated with mCPR use, while a large proportion still rely on traditional methods or use no method at all. These results underscore that targeted, age-responsive policies and programmes require improvements in education, enhanced outreach through mass media, and ensure equitable access to mCPR to reduce these disparities and improve reproductive health outcomes for women.</p>