Gradient echo imaging using in-phase echoes has been proposed to reduce the field-map estimation in water–fat regions to a convex nonlinear least squares problem. Conventionally, the in-phase assumption is based on a single-peak fat-model. However, fat is known to have a complex spectrum rendering the definition of in-phase echo times problematic. In this work, the single-fat-peak in-phase assumption is replaced by a multi-peak effective in-phase assumption. QSM based on multi-peak in-phase echo times is shown to yield similar results to water–fat imaging based field- and susceptibility-mapping in a simulation and in vivo in the spine and the breast.