Predictions of standard BBN for the primordial abundance of ⁴He (top) and deuterium (bottom), as a function of the baryon density. The width of the green stripes corresponds to 68% uncertainties on nuclear reaction rates. The horizontal bands show observational bounds on primordial element abundances compiled by various authors, and the red vertical band shows the Planck+WP+highL bounds on ω_b (all with 68% errors). BBN predictions and CMB results assume N_eff = 3.046 and no significant lepton asymmetry.