River deltas will likely experience significant land loss because of relative sea-level rise (RSLR), but predictions have remained elusive. Here, we use global data of RSLR and river sediment supply to build a validated model of delta response to RSLR for all ~10,000 deltas globally. Applying this model to predict future delta change, we find that all IPCC RCP sea-level scenarios lead to a net delta loss by the end of the 21st century, ranging from -52 ± 36 (1 s.d.) km2yr-1 for RCP2.6 to -808 ± 80 km2yr-1 for RCP8.5. We find that river dams, subsidence, and sea-level rise have had a comparable influence on reduced delta growth over the past decades, but that by 2100 under RCP8.5 more than 80% of delta land loss will be caused by climate-change driven sea-level rise.