Electron transport through a quantum-dot in the Coulomb blockade regime is modeled by a Kondo-type hamiltonian describing spin-dependent tunneling and exchange interaction with the local spin. We consider the regime of large transport voltage V and magnetic field B with max(V, B) » Tk, the Kondo temperature, and show that a renormalized perturbation theory can be formulated describing the local magnetization M and the differential conductance G quantitatively. Based on the structure of leading logarithmic corrections in bare perturbation theory we argue that the perturbative renormalization group has to be generalized to allow for frequency dependent coupling functions. We simplify the full RG equations in the spirit of poor man’s scaling and calculate M and G in leading order of 1/ln[(V, B)/T k].