Smile risk is often managed using the explicit implied volatility formulas developed for the SABR model [1]. These asymptotic formulas are not exact, and this can lead to arbitrage for low strike options. Here we provide an alternate method for pricing options under the SABR model: We use asymptotic techniques to reduce the SABR model from two dimensions to one dimension. This leads to an effective one-dimensional forward equation for the probability density which has the same asymptotic order of accuracy as the explicit implied volatility formulas. We obtain arbitrage-free option prices by numerically solving this PDE. The implied volatilities obtained from the numerical solutions closely match the explicit implied volatility curves, apart from a boundary layer at very low rates. For very low-rate environments, or for very low strikes, the implied absolute (normal) volatility dips downward, closely matching market observations. We also show how negative rates can be accommodated by replacing the F factor with (F + a) .