Constraints in the ωb–Neff plane from Planck and Planck+BAO data (68% and 95% contours) compared to the predictions of BBN, given primordial element abundance measurements. We show the 68% and 95% confidence regions derived from 4He bounds compiled by Aver et al. (2013) and from deuterium bounds compiled by Cooke et al. (2014). In the CMB analysis, Neff is allowed to vary as an additional parameter to base ΛCDM, with YP fixed as a function of ωb and Neff, according to BBN predictions. These constraints assume no significant lepton asymmetry.