Kidney Function (GFR) Calculator
Estimate your glomerular filtration rate (eGFR) with the race-free CKD-EPI 2021 creatinine equation to assess kidney function and chronic kidney disease (CKD) stage. Useful for patients and clinicians monitoring renal health.
Last updated: September 2026
Formula below · 3 sources (niddk.nih.gov, CDC, Wikipedia) · Updated Sep 2026
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About this calculator
This calculator uses the CKD-EPI 2021 creatinine equation, the race-free equation recommended by the National Kidney Foundation and American Society of Nephrology Task Force in 2021 and now reported by most US laboratories. It replaces the older four-variable MDRD equation (175 × Scr^−1.154 × age^−0.203 × 0.742 if female × 1.212 if African American), which underestimates GFR above 60 and used a race multiplier. The 2021 equation is eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^age × 1.012 (if female), with κ = 0.7 (female) or 0.9 (male) and α = −0.241 (female) or −0.302 (male). Serum creatinine in mg/dL is the primary input (divide µmol/L by 88.4), as creatinine is a waste product filtered by the kidneys — higher levels reflect lower filtration capacity. The 0.9938^age term captures the decline in GFR with aging, and the sex terms account for average differences in muscle mass and creatinine production. Results are reported in mL/min/1.73 m² and mapped to CKD stages G1 through G5, ranging from normal (≥90) to kidney failure (<15).
How to use
Example: A 55-year-old woman with serum creatinine of 1.2 mg/dL. Step 1: κ = 0.7 and α = −0.241 (female); Scr/κ = 1.2/0.7 = 1.714. Step 2: min(1.714, 1) = 1, so the α term is 1. Step 3: max(1.714, 1)^−1.200 = 1.714^−1.200 ≈ 0.524. Step 4: age term = 0.9938^55 ≈ 0.710. Step 5: multiply — 142 × 0.524 × 0.710 × 1.012 ≈ 53.5 mL/min/1.73 m². This places the patient in CKD Stage G3a (moderately decreased, 45–59) if it persists for 3 months. A 50-year-old man with the same creatinine gets 73.7 (Stage G2, mildly decreased).
Frequently asked questions
What is a normal eGFR and what do the different CKD stages mean?
An eGFR of 90 mL/min/1.73 m² or above is considered normal kidney function (CKD Stage G1, if other markers of kidney damage are present). Stage G2 (60–89) indicates mildly decreased function, often with no symptoms. Stages G3a (45–59) and G3b (30–44) represent moderate reduction, where complications like anemia and bone disease may emerge. Stage G4 (15–29) is severely decreased function requiring preparation for renal replacement therapy. Stage G5 (below 15) is kidney failure, typically requiring dialysis or transplantation. Regular monitoring is critical because many patients reach advanced stages before experiencing noticeable symptoms.
Why does this calculator use CKD-EPI 2021 instead of the MDRD equation?
The MDRD equation was widely used for detecting moderate-to-severe kidney impairment (eGFR below 60), but it tends to underestimate GFR in people with normal or near-normal kidney function and it includes a race coefficient. The CKD-EPI equations are more accurate above 60, and the 2021 refit removed race, so the NKF-ASN Task Force recommends CKD-EPI 2021 for routine reporting in the US. Results can still be affected by non-renal factors influencing creatinine levels, such as high dietary meat intake, muscle-wasting conditions, or certain medications. All eGFR formulas are estimates of true GFR, not direct measurements; adding cystatin C or measuring GFR with iohexol clearance gives a more precise answer when it matters.
Why does this calculator not ask for race?
The MDRD race multiplier of 1.212 for individuals classified as African American was derived from the original MDRD study population, which found systematic differences in measured versus predicted GFR between racial groups, attributed primarily to differences in average muscle mass and creatinine generation rates. However, this multiplier has been increasingly criticized because race is a social construct, not a biological variable, and using it can perpetuate health disparities by potentially delaying CKD diagnosis in Black patients. The CKD-EPI 2021 equation used here was refit without the race variable to improve equity and accuracy across populations, so the calculator does not ask for it. If you are using this result clinically, discuss with your physician which equation your laboratory reports.