Abstract Background and Aims Quantifying the kidney function is crucial for diagnosing and monitoring kidney disorders in clinical practice. Recently, the CKD-EPI 2021 formula was developed for estimating glomerular filtration rate (eGFR), excluding the ethnicity variable. In this study, we aimed to analyze the impact in a Dutch routine-care cohort of introducing the new serum creatinine-based CKD-EPI 2021 formula on glomerular kidney function estimation and the prevalence of chronic kidney disease (CKD), compared to the now used CKD-EPI 2012 formula. Method All patients of 18 years and older of whom serum creatinine was measured between January 2013 and December 2023 at the University Medical Center Utrecht in the Netherlands, were included. Differences in the eGFR measured with the CKD-EPI 2012 formula and the new CKD-EPI 2021 formula were defined as median difference, stratified by gender, age categories, and CKD stages. Results 251.960 patients with 2.312.313 serum creatinine measurements were included in our analysis. Our findings indicate that the CKD-EPI 2021 formula results in a higher eGFR compared to the CKD-EPI 2012 formula (median +3.6 (Inter quartile range (IQR) 2.4 to 4.5) ml/min/1.73 m2 in men, and median +3.1 (IQR 2.0 to 4.0) ml/min/1.73 m2 in women). In total, 21.1% of the patients with CKD stage 2-5 according to the CKD-EPI 2012 formula were classified as having a better CKD stage using the new CKD-EPI 2021 formula; 26.1%, 20.5%, and 15.1% of the patients classified as having CKD stage 3A, 3B, and 4 were classified as having CKD stage 2, 3A, and 3B, respectively (Table 1). Conclusion The introduction of the CKD-EPI 2021 formula would have significant implications for kidney function estimation in the Dutch clinical setting. It is crucial to consider these differences when interpreting kidney function data and making clinical decisions, especially given the potential impact on diagnosing CKD and dosing medication.