The invention relates to a method and device for predetermining treatment parameters for an extra-corporal dialysis treatment with a dialyser (1) subdivided by a semipermeable membrane (2) into a blood chamber (3) and a dialysis liquid chamber (4). Blood flows at a predetermined blood flow rate Q<；SUB>；b<；/SUB>； through the blood chamber, and dialysis liquid flows at a predetermined dialysis liquid flow rate Q<；SUB>；d<；/SUB>； through the dialysis liquid chamber. The method and device according to the invention for predetermining treatment parameters involve the determination of the dialysis dose real value of a dialysis treatment and the predetermination of the dialysis dosis set value for a subsequent dialysis treatment with a particular treatment time. The clearance for the subsequent treatment is then calculated from the dialysis dosis real value and the dialysis dosis set value.
