Migration to Zero-Offset (MZO) or Prestack Partial Migration (PSPM) transforms prestack data into zero-offset data and is equivalent in a constant velocity medium to normal moveout correction (NMO) followed by the dip moveout correction (DMO) applied as a single step process. I present an algorithm to construct the MZO operator in variable velocity media as a potentially efficient alternative to full prestack migration. The MZO impulse response is computed using finite-difference travel-time maps, by considering the MZO process as the combination of full prestack migration followed by zero-offset modeling. The generalized impulse response can be applied to the data as an integral operator. I apply the operator to different synthetic models with depth variable velocity and show the improvements in stacking alignment over conventional DMO and NMO processing.