INTRODUCTION: A strong focus on sexual and reproductive health of female adolescents is a key to achieving sustainable development goals, due to the large size of the current cohort in low-income and middle-income countries (LMICs) and adolescents' biological and social vulnerability. Several indicators of fertility among adolescents are in wide use, but the contribution of adolescent births to all births is poorly understood. We propose and calculate a package of three indicators capturing the contribution of adolescent births to all births, stratified by parity (first and second/higher). METHODS: We used Demographic and Health Survey data for 30 LMICs and vital registration for two high-income countries (to calculate levels and trends across a range of countries) for three time periods: 1990-1999, 2000-2009 and 2010-2015. The three indicators were calculated overall and by age thresholds (<16, <18  and <20  years) and exact ages, for each country and time point. Patterns of changes in indicators for the three cumulative thresholds over time are described. RESULTS: In the 30 LMICs, the percentage of all live births occurring to adolescents varied across countries, with a median of 18% for adolescents <20  years. Three countries (Jordan, Indonesia and Rwanda) had levels below 10%; Bangladesh had the highest at 33%. The contribution of adolescent first-order births to all first-order births was high; a median of 49%. Even among second-order and higher-order births, the contribution of adolescent childbearing was appreciable (median of 6%). Over the period under examination, the proportion of adolescent births among all live births declined in the majority of the LMICs. CONCLUSION: These three indicators add to our understanding of the scale of adolescent childbearing and can be used in conjunction with population estimates to assess the absolute need for age-appropriate and parity-appropriate reproductive, maternal and newborn healthcare and to monitor progress in improving young people's health.