An apparatus for extracorporeal blood treatment is described, including a treatment unit, an extracorporeal blood circuit, an infusion line of a replacement fluid, a dialysis line connected in inlet to the second chamber, and a fluid evacuation line; sensors for determining a first parameter relating to a patient's blood volume (BV %) a second parameter relating to an ultrafiltration flow rate (UFR) or to a patient's weight loss rate (WLR), a third parameter (Cd, Na) relating to a conductivity or concentration of a liquid crossing the dialysis line and/or the infusion line, and a fourth parameter relating to an infusion flow rate (QINF), and a control unit for performing a control procedure.