Abstract Sumatra is located at the western end of the Sunda Arc, which resulted from the subduction of the Indo-Australian Plate beneath the Eurasian Plate. In this study, we report detailed zircon U–Pb and Hf isotope data for Cenozoic igneous rocks from the entire island of Sumatra to better constrain the temporal and spatial distribution of arc magmatism. The new dataset, combined with literature information, identifies the following two magmatic stages: (1) Paleocene to Early Eocene (66–48 Ma) and (2) Early Miocene to Recent (23–0 Ma), with a 25 myr-long period of magmatic quiescence in between. The magmatic zircons show predominantly positive and high ε Hf (t) values, ranging from +19.4 to +7.1 in western Sumatra, +17.1 to +1.6 in central Sumatra and +18.0 to +7.0 in eastern Sumatra, indicating an isotopically juvenile magma source in the mantle wedge along the western Sunda Arc. We explain the negative and low ε Hf (t) values (+0.5 to −13.1) of young samples around the supervolcano Toba as evidence for the subduction of sediment. We argue for a change in the subduction processes, where the first magmatic stage ceased owing to the termination of the Neo-Tethyan subduction and the following stage corresponded to the modern Sunda subduction.