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We determined the performance of estimated glomerular filtration rate equations (eGFR) including MDRD2-Isotope Dilution Mass Spectrometry (MDRD2-IDMS), Cockcroft-Gault (CG) and Virga to measure post-transplant chronic kidney disease (CKD) stages 1-4, using simultaneous isotope GFR (iGFR) measurement. The study was conducted in 97 patients. The eGFR results measured by CG and Virga were normalized to 1.73 m 2 . Analysis of relative and absolute bias, error, scatter, correlation coefficient of variance and accuracy within the 30% range from the reference iGFR result was performed using standard techniques. There were 135, 242, 314 and 82 scans, respectively, in CKD stages 1-4. Bias and accuracy of GFR estimators varied significantly across the CKD stages. In stages 1 and 2, CG had the best error of -12.7 and 0.2 mL/min/1.73 m 2 , respectively, while Virga had the highest accuracy of 74.3% and 85.5, respectively. In stages 3 and 4, MDRD2-IDMS had the best error of -0.52 and 5.8, respectively. Accuracy was the best at 75.1% for Virga in stage 3, while it was the highest of 70.7% for MDRD2-IDMS in stage 4. Virga had the highest accuracy of 75.2% in stage 4. The worst bias was for MDRD2-IDMS in stage 2 (-36.8 mL/min/1.73 m 2 ) and the best bias was for CG in stage 2 (-0.33 mL/min/1.73 m 2 ). The eGFR estimators have inconsistent performances in the various stages of CKD and, thus, another limitation is added to their validity to substitute for the gold standard methods.