Using different techniques, and Fermi-liquid relationships, we calculate the variation with applied magnetic field (up to second order) of the zero-temperature equilibrium conductance through a quantum dot described by the impurity Anderson model. We focus on the strong-coupling limit $U gg Delta$ where $U$ is the Coulomb repulsion and $Delta$ is half the resonant-level width, and consider several values of the dot level energy $E_d$, ranging from the Kondo regime $epsilon_F-E_d gg Delta$ to the intermediate-valence regime $epsilon_F-E_d sim Delta$, where $epsilon_F$ is the Fermi energy. We have mainly used density-matrix renormalization group (DMRG) and numerical renormalization group (NRG) combined with renormalized perturbation theory (RPT). Results for the dot occupancy and magnetic susceptibility from DMRG and NRG+RPT are compared with the corresponding Bethe ansatz results for $U rightarrow infty$, showing an excellent agreement once $E_d$ is renormalized by a constant Haldane shift. For $U < 3 Delta$ a simple perturbative approach in $U$ agrees very well with the other methods. The conductance decreases with applied magnetic field for dot occupancies $n_d sim 1$ and increases for $n_d sim 0.5$ or $n_d sim 1.5$ regardless of the value of $U$. We also relate the energy scale for the magnetic-field dependence of the conductance with the width of low energy peak in the spectral density of the dot.
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