Analysis of the standard SABR model leads to an effective forward equation which has time-independent coefficients, and analysis of this reduced-dimensionality equation leads to explicit asymptotic formulas for the implied normal volatilities of European options. These formulas are accurate to within O( 2 ), and are used extensively in practice for pricing and managing the risks of European options. A recent analysis of the dynamic SABR model leads to an identical effective forward equation, except that the coefficients are time-dependent. Here we use singular perturbation methods to analyze this new equation. For each exercise date T ex , we derive a set of constant coefficients. Replacing the time-dependent coefficients with the constant coefficients, and solving the effective forward equation, yields the correct probability density function -and thus the correct European option values -to within O ( 2 ) . These constant coefficients now let us apply the existing analysis to obtain explicit asymptotic formulas for the implied volatilities of European options, accurate to within O ( 2 ) , for the dynamic SABR model. Current analyses of several other stochastic volatility models, including the -SABR and generalized Heston models, also yield identical effective forward equations with time-dependent coefficients. Therefore, the implied volatilities for these models are also given by the SABR implied volatility formulas.