Glomerular filtration rate (GFR) is the amount of blood cleared by the kidneys over a given period of time. GFR is the main indicator for assessing renal function and stage renal failure. In clinical practice, GFR is calculated using special formulas based on the concentration of creatinine in the blood and some anatomical and physiological parameters (height, weight, age). The presented calculator calculates using the Cockroft-Gault formulas, MDRD and the CKD-EPI equation. GFR in children is calculated according to the formula of Schwartz and Counahan-Barratt.