GFR Kidney Function Calculator

Your kidneys play a vital role in filtering waste products and excess fluid from your blood. The Glomerular Filtration Rate (GFR) is the best overall measure of how well your kidneys are performing this essential function. An estimated GFR (eGFR) is routinely calculated from a simple blood test that measures creatinine -- a waste product produced by your muscles -- along with your age and sex. Chronic kidney disease (CKD) affects approximately 1 in 10 people worldwide, and many are unaware they have it until the disease has progressed significantly. In the UK, the NHS uses eGFR as the primary tool for diagnosing and staging CKD. Early detection through routine blood tests allows for interventions that can slow or prevent further kidney damage. This calculator uses the CKD-EPI 2021 equation, the most recent and recommended formula for estimating GFR. The 2021 revision, published in the New England Journal of Medicine, removed the race coefficient that was present in earlier versions, providing a single, equitable equation for all patients. It is the formula recommended by NICE for use in UK clinical practice.

How to Use This Calculator

To estimate your kidney function: 1. Enter your serum creatinine level in micromoles per litre (umol/L). This value comes from a routine blood test. Normal ranges are approximately 59-104 umol/L for men and 45-84 umol/L for women, though this varies by laboratory. 2. Enter your age in years. GFR naturally declines with age, so older adults will generally have lower eGFR values. The calculator is designed for adults aged 18 and over. 3. Select your sex (male or female). The CKD-EPI equation uses different coefficients for males and females because of differences in average muscle mass and creatinine production. 4. Review your results. The calculator displays your estimated GFR in mL/min/1.73m2, your CKD stage (G1 to G5), a description of your kidney function level, and recommendations based on NICE guidelines.

How It Works

The CKD-EPI 2021 equation estimates GFR from serum creatinine, age, and sex. The formula first converts creatinine from umol/L to mg/dL by dividing by 88.42, then applies different equations depending on sex and creatinine level: For females with creatinine 62 umol/L (0.7 mg/dL) or below: eGFR = 142 x (creatinine/0.7)^-0.241 x 0.9938^age x 1.012 For females with creatinine above 62 umol/L: eGFR = 142 x (creatinine/0.7)^-1.200 x 0.9938^age x 1.012 For males with creatinine 80 umol/L (0.9 mg/dL) or below: eGFR = 142 x (creatinine/0.9)^-0.302 x 0.9938^age For males with creatinine above 80 umol/L: eGFR = 142 x (creatinine/0.9)^-1.200 x 0.9938^age CKD stages based on eGFR: G1 (90 or above, normal), G2 (60-89, mildly reduced), G3a (45-59, mildly to moderately reduced), G3b (30-44, moderately to severely reduced), G4 (15-29, severely reduced), G5 (below 15, kidney failure). A single eGFR reading does not confirm CKD -- the NICE guideline requires two results at least 90 days apart showing eGFR below 60 before diagnosing CKD.

The CKD-EPI 2021 equation replaced the older CKD-EPI 2009 and MDRD equations. The key change in the 2021 revision was the removal of the race coefficient, which had been criticised for potentially underestimating kidney disease severity in Black patients. The new equation uses the same formula for all ethnic groups. Creatinine-based eGFR has limitations. It can be affected by muscle mass, diet (particularly high-protein diets), certain medications, and acute illness. For a more accurate assessment, your doctor may also test for cystatin C, another marker of kidney function that is less affected by muscle mass. If your eGFR is below 60 or declining rapidly, your GP should refer you according to NICE CKD guideline NG203. Key referral criteria include eGFR below 30, rapid decline (more than 25% drop or more than 15 mL/min/1.73m2 drop within 12 months), and significant proteinuria. Reference: NICE CKD guideline NG203, Inker LA et al. New Creatinine- and Cystatin C-Based Equations (NEJM 2021), NHS Kidney disease information (nhs.uk/conditions/kidney-disease).