A measurement of the top-antitop charge asymmetry is underway at the ATLAS experiment at the LHC. This is being being performed at 13 TeV with 80 fb-1 of proton-proton collision data, with the eventual aim to use the full 140 fb-1 Run 2 dataset. The method of Fully Bayesian Unfolding (FBU) is employed to determine the parton-level charge asymmetry. This technique generates a posterior probability distribution for the asymmetry which we compare with the expectation from Monte-Carlo simulation. The method also helps to reduce the systematic uncertainties and will allow the combination of three ttbar decay channels: dilepton, lepton+jets with resolved jets and lepton+jets with boosted (collimated) jets. The asymmetry is expected to be small, though effects beyond the Standard Model can change this. It is being determined inclusively and also in bins of top-antitop transverse momentum, mass and velocity. In addition to the asymmetry for the top-antitop pair, a measurement is made in the dilepton channel of the asymmetry between the two leptons. This has reduced uncertainties but the predicted asymmetry is smaller.