Our study aimed to establish the best prediction equation for different age ranges in estimating Glomerular Filtration Rate (GFR) in clinical practice in Slovakia. The GFR by 24-hour creatinine clearance (Ccr) and the estimated GFR (eGFR) using the Cockcroft-Gault (CG), the four-variable Modification of Diet in Renal Disease (MDRD4) and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations were obtained in adults aged 30-80 (n = 433, 10-years intervals). The correlation between these prediction equations and Ccr was evaluated. Errors in prediction equations were detected by moving average and by comparisons of the formulas for GFR < 1.5 ml/s and > 1.5 ml/s. The best correlations were established between Ccr and MDRD4 for women (r = 0.7790) and men (r = 0.8009), and between Ccr and CKD-EPI for women (r = 0.7780) and men (r = 0.8002) in the 60-69 age range. High correlation was also established between Ccr and CG (r = 0.8655) and MDRD4 (r = 0.8713) for men in the 40-49 age range. With the exception of the 30-40 age range, a low prediction error was observed for each age range in both genders when GFR was < 1.5 ml/s. We recommend utilization of the MDRD4 and CG equations for men (40-49 years) and MDRD4 and CKD-EPI for women and men (60-69 years), as preferred substitutes for Ccr.