A process is proposed for preparing acid formates by providing a liquid stream I containing formic acid and a liquid stream II containing a metal formate, and mixing the liquid stream I with the liquid stream II, obtaining the corresponding acid formate, which comprises feeding, to the liquid stream I or a precursor thereof, to the liquid stream II or a precursor thereof, or to the mixture of the liquid streams I and II, a liquid stream III containing the following components at contents of in each case >0.1% by weight: metal formate, metal methoxide, methanol and MeFo (MeFo), which is produced in a process for preparing MeFo by carbonylating methanol in a reactor at a pressure up to 50 MPa absolute in the presence of a metal methoxide as homogeneous catalyst.