The zero-bias conductance peak in d-wave superconductors splits in an applied magnetic field. In this work, the experimentally observed universal relation delta ~ B0^(1/2) for strip-shaped samples is derived analytically based on the long-ranged current contributions from Abrikosov vortices inside the sample. The result is in full agreement with observed key properties, and features such as hysteresis effects are made accessible. Employing a magnetically induced additional order parameter is not necessary for the physical explanation of the universal relation.