Digital grids of basement age of the world's oceans are essential for modern geodynamic and paleoceanographic studies. Any such grid is built using a plate kinematic model, whose accuracy and reliability directly influence the accuracy and reliability of the grid. We present a seafloor age grid for the South Atlantic based on a recent high-resolution plate kinematic model. The grid is built from a data set of points whose ages are defined in or for the plate kinematic model, incorporating breaks at tectonic boundaries like fracture zones where the age function is discontinuous. We compare predictions of the new grid and of a previously published one, which is based on an older plate kinematic model, to magnetic isochron pick data sets. The comparison shows the new grid to provide a more reliable depiction of seafloor age in the South Atlantic. Numerical estimates of the new grid's uncertainty are determined by interpolation between (1) misfits at grid cells coinciding with magnetic isochron ages, (2) misfits implied by locational uncertainties in predicted isochrons propagated from uncertainties in the plate kinematic model, and (3) by the proximities of cells to fracture zone traces or ridge-jump scars. Estimated total uncertainty is <10 My for 94% of the grid and <5 My for 72%, but much larger in areas where magnetic anomaly data are scarce (such as the Cretaceous Normal Superchron) and in the vicinity of long-offset fracture zones.