GFR Calculator
Estimate your glomerular filtration rate with CKD-EPI 2021, MDRD, and Cockcroft-Gault formulas
Enter your serum creatinine from a blood test. Switch units using the toggle above.
Age in years (18-120). GFR naturally declines with age.
Biological sex affects the sex-specific constants in GFR equations.
Enter Your Results Above
Input your serum creatinine, age, and biological sex to calculate your eGFR and CKD stage across multiple formulas.
How to Use the GFR Calculator
Enter Your Serum Creatinine
Find your serum creatinine value on a blood test report (a standard metabolic panel or kidney function panel includes this). Toggle between mg/dL (used in the US) and µmol/L (used in most other countries) to match your lab report. Typical adult values range from 0.5 to 1.2 mg/dL (44 to 106 µmol/L). Higher values generally indicate reduced kidney function.
Enter Age and Biological Sex
Type your age in years and select your biological sex (Male or Female). These are required for all GFR equations. The sex selection affects the sex-specific constants (kappa and alpha) in the CKD-EPI formulas. Age directly appears in the exponent of both CKD-EPI and MDRD equations — GFR naturally declines with age, so the formulas account for this.
Add Optional Inputs for More Results
Expand the Advanced Options section to enter additional values. Weight (kg or lbs) enables the Cockcroft-Gault creatinine clearance calculation — useful for checking medication dose thresholds. Height (cm or inches) combined with weight enables BSA-adjusted absolute GFR. Serum Cystatin C (mg/L) unlocks two additional equations. ACR (albumin-to-creatinine ratio) category enables the KDIGO risk matrix, which shows your combined kidney disease and cardiovascular risk.
Review the Side-by-Side Formula Comparison
Click Calculate eGFR to see all results simultaneously. The primary CKD-EPI 2021 result appears prominently with your CKD stage. The formula comparison table shows CKD-EPI 2021, CKD-EPI 2009, MDRD, and Cockcroft-Gault side by side — making it easy to compare how different equations interpret the same values. The kidney function spectrum gauge shows your position within the G1-to-G5 range visually.
Frequently Asked Questions
What is a normal eGFR, and does it change with age?
A normal eGFR is typically 90 mL/min/1.73 m² or above for adults. GFR naturally declines with age at approximately 1 mL/min per year after age 40, which is why an eGFR of 75 in a 70-year-old may not indicate disease, while the same value in a 30-year-old would be concerning. The population reference chart in this calculator shows typical eGFR values by decade: roughly 116 for ages 20-29, dropping to 85 for ages 60-69, and 75 for ages 70 and over. Whether a given eGFR represents CKD depends on whether kidney damage markers (like protein in urine) co-exist and whether the finding persists for at least three months. Always review your result in the context of your age and medical history with your doctor.
Why does the CKD-EPI 2021 formula no longer use race?
The original CKD-EPI 2009 equation included a multiplier of 1.159 for patients identified as Black, based on population studies showing higher average muscle mass and creatinine production in Black individuals. However, this approach was criticized for assigning a biological characteristic to a socially defined category, and its application led to Black patients being assigned systematically higher eGFR values — and consequently later referrals to nephrology. An NKF-ASN Task Force reviewed the evidence in 2021 and concluded that race should not be a variable in kidney function equations. The new 2021 CKD-EPI formula uses only creatinine, age, and sex. The change may lower the eGFR for some patients who were previously using the Black race coefficient, which could lead to earlier identification and treatment of CKD.
What is the difference between eGFR and creatinine clearance (Cockcroft-Gault)?
eGFR from CKD-EPI or MDRD is expressed in mL/min/1.73 m² — it is normalized to a standard body surface area of 1.73 m², making it comparable across patients of different body sizes. Creatinine clearance (CrCl) from the Cockcroft-Gault formula is expressed in mL/min without body surface area normalization. CrCl tends to slightly overestimate true GFR because creatinine is not only filtered but also secreted by renal tubules. Despite this, Cockcroft-Gault remains the standard reference in drug prescribing information because it was the equation used in most pharmacokinetic studies. When checking medication dose thresholds — for example, whether to use metformin or how to dose a direct oral anticoagulant — always use Cockcroft-Gault CrCl, not eGFR.
When is the MDRD equation used instead of CKD-EPI?
The MDRD (Modification of Diet in Renal Disease) Study Equation was the standard eGFR formula from 1999 until CKD-EPI was introduced in 2009. MDRD is less accurate than CKD-EPI when eGFR is above 60 mL/min/1.73 m² — it tends to underestimate eGFR in this range, which can lead to overdiagnosis of CKD. CKD-EPI 2021 is now recommended for all adults in clinical practice. However, MDRD may still appear in some older laboratory systems that have not yet updated their reporting, and it remains useful for reference and comparison purposes. This calculator shows MDRD alongside CKD-EPI so you can see how the two equations differ for your specific inputs.
What does the KDIGO risk matrix mean, and when is referral to a nephrologist needed?
KDIGO (Kidney Disease: Improving Global Outcomes) risk stratification combines your GFR category (G1-G5) with your albuminuria category (A1, A2, or A3 based on urine albumin-to-creatinine ratio). Together, these two dimensions create a heat map of risk from Low to Very High. Low risk means annual monitoring in primary care is sufficient. Moderately Increased risk generally means monitoring every 6 months. High risk warrants every 3-month checks. Very High risk requires monthly to 3-monthly monitoring and specialist nephrology care. Referral to a nephrologist is typically recommended when eGFR is below 30 mL/min/1.73 m² (G4-G5), when eGFR is declining rapidly (more than 5 mL/min/1.73 m² per year), when ACR is in the severely increased category (A3), or when the cause of kidney disease is uncertain.
Can medications or other factors falsely alter my creatinine and eGFR?
Yes, several factors can affect serum creatinine independent of actual kidney function, which leads to either falsely high or falsely low eGFR. Medications that reduce creatinine secretion without harming the kidney include trimethoprim, cimetidine, and certain diabetes drugs — these raise creatinine and lower apparent eGFR. High dietary meat intake can transiently raise creatinine. Strenuous exercise increases creatinine for 24-48 hours. Conversely, very low muscle mass (elderly, amputees, malnutrition) produces less creatinine, artificially lowering it and inflating eGFR. Dehydration concentrates creatinine, lowering apparent eGFR. Pregnancy lowers creatinine and inflates eGFR. For these reasons, eGFR from creatinine alone is considered less reliable in these special populations, and Cystatin C-based or combined equations may be more accurate.