Expanding access to contraception and ensuring that need for family planning is satisfied are essential for achieving universal access to reproductive healthcare services, as called for in the 2030 Agenda for Sustainable Development. To quantify the gaps that remain in meeting needs among adolescents, this study provides a harmonised data set and global estimates and projections of family planning indicators for adolescents aged 15-19 years. We compiled a comprehensive dataset of family-planning indicators among women aged 15-19 from 754 nationally representative surveys. We used a Bayesian hierarchical model with country-specific annual trends to estimate contraceptive prevalence and unmet need for family planning, with 95% uncertainty intervals (UIs), for 185 countries, taking into account changes in proportions married or in a union and differences in sexual activity among unmarried women across countries. Among 300 million women aged 15-19 years in 2019, 29.8 million (95% UI 24.6-41.7) use any contraception, and 15.0 million (95% UI 12.1-29.2) have unmet need for family planning. Population growth and the postponement of marriage influence trends in the absolute number of adolescents using contraception or experiencing unmet need. Large gaps remain in meeting family-planning needs among adolescents. The proportion of the need satisfied by modern methods, Sustainable Development Goals (SDG) indicator 3.7.1, was 59.2% (95% UI 44.8-67.2) globally among adolescents, lower compared to 75.7% (95% UI 73.2%-78.0%) among all women age 15-49 years. It was less than one half of adolescents in need in Western Asia and Northern Africa (38.7%, 95%UI = 20.9-56.5), Central and Southern Asia (43.5%, 95%UI = 36.6-52.3), and sub-Saharan Africa (45.6%, 95%UI = 42.2-49.0). The main limitations of the study are: (i) the uncertainty surrounding estimates for countries with limited or biased data is large; and (ii) underreporting of contraceptive use and needs is likely, especially among unmarried adolescents.