Enter serum creatinine, age, and sex to estimate glomerular filtration rate (eGFR) and see the corresponding CKD stage.
How to Use the GFR Calculator
Enter serum creatinine in mg/dL, your age, and select Male or Female — the eGFR value and CKD stage below update immediately with every change, no separate submit step.
Kidneys filter roughly 180 liters of blood plasma a day in a healthy adult, and glomerular filtration rate is the number describing how fast. Nobody measures it directly in routine care — the gold-standard method involves injecting and tracking a filtration marker through the bloodstream, impractical for an ordinary checkup. Labs estimate it instead from a blood test you likely already have: serum creatinine.
The 2021 CKD-EPI Creatinine Equation
κ = 0.7 (female) or 0.9 (male)
α = −0.241 (female) or −0.302 (male)
eGFR = 142 × min(Scr÷κ, 1)^α × max(Scr÷κ, 1)^−1.2 × 0.9938^Age × 1.012 (if female)Scr is serum creatinine in mg/dL. This is the 2021 CKD-EPI Creatinine equation, published by Lesley Inker and colleagues in the New England Journal of Medicine in 2021 — the version the National Kidney Foundation and the American Society of Nephrology now recommend labs use.
The equation it replaced included a coefficient that multiplied results upward for patients recorded as Black, built on the assumption that Black patients have, on average, higher creatinine at the same true GFR due to differences in muscle mass. That population-level assumption, applied to individuals, had a real consequence: it could make a Black patient's kidney function look better than it actually was, delaying referrals, transplant workups, and other care a lower reported number would have triggered sooner. The 2021 NEJM effort refit the equation from scratch on new data and removed the race coefficient entirely rather than adjusting it — the same formula now applies to everyone.
Sex and age are the only two variables the equation looks at besides creatinine itself. That's a deliberate simplification, and also its biggest limitation — nothing here accounts for muscle mass, diet, hydration, or whether the blood draw happened right after a hard workout, all of which move creatinine independent of actual kidney function.
What This Number Doesn't Tell You
An eGFR from one blood draw is a screening estimate, not a diagnosis. Chronic kidney disease is generally defined by reduced function, or other markers of kidney damage, persisting for three months or longer — a single low or high reading proves nothing by itself, since creatinine shifts with hydration, recent exertion, certain medications, and lab-to-lab variation. Real staging happens in a doctor's office alongside a repeat test, a urine albumin measurement, and clinical context — sometimes with a cystatin C-based or combined equation layered in, since cystatin C isn't affected by muscle mass the way creatinine is. This calculator also assumes an IDMS-traceable, standardized creatinine value from an accredited lab; it has no way to verify that, and a result from a non-standardized assay won't line up with what the equation expects.
This is a screening estimate, not a diagnosis. eGFR from a single creatinine value cannot diagnose kidney disease on its own. If your result concerns you, or you have known kidney risk factors, talk to a doctor — proper evaluation and staging require repeat testing and clinical judgment this calculator doesn't have access to.