An accurate estimate of glomerular filtration rate (eGFR) is essential for proper clinical management, especially in patients with kidney dysfunction. This prospective observational study evaluated the real-world performance of the nuclear magnetic resonance (NMR)-based GFRNMRequation, which combines creatinine, cystatin C, valine, and myo-inositol with age and sex. We compared GFRNMRperformance to that of the 2021 CKD-EPI creatinine and creatinine-cystatin C equations (CKD-EPI2021Crand CKD-EPI2021CrCys), using 115 fresh routine samples of patients scheduled for urinary iothalamate clearance measurement (mGFR). Median bias to mGFR of the three eGFR equations was comparably low, ranging from 0.4 to 2.0 mL/min/1.73 m2. GFRNMRoutperformed the 2021 CKD-EPI equations in terms of precision (interquartile range to mGFR of 10.5 vs. 17.9 mL/min/1.73 m2for GFRNMRvs. CKD-EPI2021CrCys;p= 0.01) and accuracy (P15, P20, and P30 of 66.1% vs. 48.7% [p= 0.007], 80.0% vs. 60.0% [p< 0.001] and 95.7% vs. 86.1% [p= 0.006], respectively, for GFRNMRvs. CKD-EPI2021CrCys). Clinical parameters such as etiology, comorbidities, or medications did not significantly alter the performance of the three eGFR equations. Altogether, this study confirmed the utility of GFRNMRfor accurate GFR estimation, and its potential value in routine clinical practice for improved medical care.