A computer-implemented method for determining or approximating a daily loss of iron (fe_loss) of a patient who suffers from impaired renal function or cancer and/or requires dialysis, the method comprising the steps: - determining the patient's iron uptake (fe_uptake) cumulated over a certain period of time; - determining the development of the quantity of ferritin as a marker of iron stored within the patient's body outside of haemoglobin (Hb) over the certain period of time; and - determining the quantity of iron stored within the haemoglobin (Hb) over the certain period of time; - determining or approximating the patient's daily loss of iron based on the patient's cumulated iron uptake (fe_uptake) and the quantity of iron stored within the patient's body by: - determining a ferritin curve indicating the development of ferritin measurements over time; - assuming at least three different constant values for a constant daily loss of iron; - determining, for each of the assumed constant iron loss values, a curve that reflects changes in the concentration of the iron stored within the patient's body based on the haemoglobin (Hb) as the functional iron, the cumulated loss of iron due to the assumed constant daily loss of iron and the cumulated iron uptake (fe_uptake); - determining a statistic correlation by relating the ferritin curve of the patient to the curve that reflects the change in the concentration of iron stored in the patient's body; and - determining or setting the value of the assumed constant daily loss of iron that fits best with regards to statistic correlation as the actual daily loss of iron. - determining the patient's iron uptake (fe_uptake) cumulated over a certain period of time; - determining the development of the quantity of ferritin as a marker of iron stored within the patient's body outside of haemoglobin (Hb) over the certain period of time; and - determining the quantity of iron stored within the haemoglobin (Hb) over the certain period of time; - determining or approximating the patient's daily loss of iron based on the patient's cumulated iron uptake (fe_uptake) and the quantity of iron stored within the patient's body by: - determining a ferritin curve indicating the development of ferritin measurements over time; - assuming at least three different constant values for a constant daily loss of iron; - determining, for each of the assumed constant iron loss values, a curve that reflects changes in the concentration of the iron stored within the patient's body based on the haemoglobin (Hb) as the functional iron, the cumulated loss of iron due to the assumed constant daily loss of iron and the cumulated iron uptake (fe_uptake); - determining a statistic correlation by relating the ferritin curve of the patient to the curve that reflects the change in the concentration of iron stored in the patient's body; and - determining or setting the value of the assumed constant daily loss of iron that fits best with regards to statistic correlation as the actual daily loss of iron. - determining a ferritin curve indicating the development of ferritin measurements over time; - assuming at least three different constant values for a constant daily loss of iron; - determining, for each of the assumed constant iron loss values, a curve that reflects changes in the concentration of the iron stored within the patient's body based on the haemoglobin (Hb) as the functional iron, the cumulated loss of iron due to the assumed constant daily loss of iron and the cumulated iron uptake (fe_uptake); - determining a statistic correlation by relating the ferritin curve of the patient to the curve that reflects the change in the concentration of iron stored in the patient's body; and - determining or setting the value of the assumed constant daily loss of iron that fits best with regards to statistic correlation as the actual daily loss of iron.