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Estimate kidney function (eGFR) with the CKD-EPI 2021 race-free equation and see the CKD stage.
How to use: Enter your age, sex, and serum creatinine in mg/dL from a recent blood test. The calculator applies the CKD-EPI 2021 race-free equation and maps the result to a CKD stage (G1–G5).
Formula
eGFR = 142 × min(Scr/κ,1)^α × max(Scr/κ,1)^−1.200 × 0.9938^Age × 1.012 (if female); κ = 0.7 female / 0.9 male, α = −0.241 female / −0.302 male. Example: 50-year-old man, creatinine 1.0 mg/dL → eGFR 92 (stage G1).
Estimating your glomerular filtration rate takes three inputs and about fifteen seconds with the calculator above. Enter your age in years, select your sex, and enter your serum creatinine in mg/dL — the value from your blood test report (a typical reference range is roughly 0.7–1.3 mg/dL for men and 0.6–1.1 mg/dL for women, though labs vary). Press “Calculate eGFR” to see your estimated GFR in mL/min/1.73m² and the corresponding kidney function category from G1 (normal) to G5 (kidney failure).
Use your most recent lab result, drawn when you were normally hydrated and had not done intense exercise in the prior 24–48 hours — heavy workouts temporarily raise creatinine and can depress the estimate. If your report lists creatinine in µmol/L (common outside the US), divide by 88.4 to convert to mg/dL. A single estimate is a snapshot; kidney function is judged by trends across multiple tests plus urine albumin and blood pressure, so save your results and compare over time.
Important: this calculator is for information only and is not medical advice. It cannot diagnose chronic kidney disease, which requires persistent abnormalities over at least three months confirmed by a clinician. Never start, stop, or change medication — especially NSAIDs, blood pressure drugs, or diabetes medications — based on an online estimate. If your eGFR is below 60 or falling, discuss it with your doctor promptly.
Glomerular filtration rate (GFR) is the volume of blood your kidneys filter each minute, and it is the single best overall measure of kidney function. Each kidney contains about a million nephrons — microscopic filtering units where blood passes through clusters of capillaries called glomeruli. The glomeruli sieve waste products, excess fluid, and electrolytes out of the blood into urine while keeping blood cells and large proteins in circulation. A healthy young adult filters roughly 90–120 mL every minute — about 130–170 liters per day, of which all but 1–2 liters are reabsorbed.
Because directly measuring GFR requires infusing marker substances like inulin or iohexol, clinicians use estimated GFR (eGFR) instead — a value calculated from serum creatinine, a waste product of muscle metabolism that healthy kidneys clear at a steady rate. When filtration declines, creatinine accumulates in the blood, so higher creatinine means lower eGFR. The CKD-EPI 2021 equation used by this calculator is the current clinical standard: it was refit without a race coefficient (removing the older Black race multiplier) and validated across diverse populations.
CKD stages classify kidney function by eGFR: G1 (≥90) normal or high; G2 (60–89) mildly decreased; G3a (45–59) mildly to moderately decreased; G3b (30–44) moderately to severely decreased; G4 (15–29) severely decreased; and G5 (<15) kidney failure, where dialysis or transplant is discussed. Crucially, CKD is only diagnosed when abnormalities persist for three months or more — a single low reading after dehydration or illness is not CKD. Doctors combine eGFR with albuminuria (protein in urine, graded A1–A3) to stage disease fully.
Creatinine deserves understanding because it drives the estimate. It is produced at a fairly constant rate from creatine phosphate in muscle, so muscular people run higher baseline creatinine and slight, healthy individuals lower — the same 1.1 mg/dL means different eGFRs at different muscle masses. Acute influences include dehydration (raises creatinine), heavy exercise (raises it for a day or two), high meat intake (small transient rise), and medications such as trimethoprim or cimetidine (raise measured creatinine without harming filtration). Chronic influences include age (GFR declines roughly 1 mL/min/1.73m² per year after age 40), diabetes, and hypertension — the two leading causes of CKD worldwide.
Why does eGFR matter? Chronic kidney disease affects roughly 1 in 7 US adults, yet 9 in 10 with early CKD do not know they have it, because symptoms — fatigue, swelling, appetite loss — appear only in advanced stages. Early detection through eGFR and urine albumin allows interventions (blood pressure control, diabetes management, ACE inhibitors, SGLT2 inhibitors) that can slow or halt progression. An eGFR below 60, or albumin in the urine at any eGFR, warrants medical evaluation — not panic, but a prompt appointment.
This calculator implements the CKD-EPI 2021 creatinine equation (race-free), the standard adopted by KDIGO and the US National Kidney Foundation:
eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^(−1.200) × 0.9938^Age × 1.012 (if female)
Where Scr is serum creatinine in mg/dL, κ is 0.7 for females and 0.9 for males, α is −0.241 for females and −0.302 for males, and the final 1.012 multiplier applies only to females. The min/max structure makes the equation gentler when creatinine is below the κ threshold and steeper above it, mirroring real physiology. Results are reported normalized to a standard body surface area of 1.73 m².
Worked example 1. A 50-year-old man with Scr 1.0 mg/dL. κ = 0.9, α = −0.302. Scr/κ = 1.0 ÷ 0.9 = 1.111. min(1.111, 1) = 1, so the first term is 1^(−0.302) = 1. max(1.111, 1) = 1.111, and 1.111^(−1.200) ≈ 0.8813. Age term: 0.9938^50 ≈ 0.7327. eGFR = 142 × 1 × 0.8813 × 0.7327 = 91.7 ≈ 92 mL/min/1.73m² — category G1, normal or high. This matches the calculator’s default output.
Worked example 2. A 65-year-old woman with Scr 1.2 mg/dL. κ = 0.7, α = −0.241. Scr/κ = 1.2 ÷ 0.7 = 1.714. min term = 1. max term: 1.714^(−1.200) ≈ 0.5237. Age term: 0.9938^65 ≈ 0.6675. Female multiplier: 1.012. eGFR = 142 × 1 × 0.5237 × 0.6675 × 1.012 = 50.2 ≈ 50 mL/min/1.73m² — category G3a, mildly to moderately decreased. Note how the same creatinine (1.2) yields a much lower eGFR here than a younger man’s would — age and sex adjustments are doing real work, because a 65-year-old woman is expected to produce less creatinine at any given filtration rate.
The equation’s behavior is worth grasping. Because creatinine sits in the denominator with an exponent near −1.2, small creatinine changes move eGFR a lot at low creatinine (going from 0.8 to 1.0 drops eGFR ~20%) and less at high creatinine. The 0.9938^Age term quietly subtracts about 0.6% per year — the expected age-related decline. And the equation assumes stable creatinine; during acute kidney injury, creatinine lags behind real filtration changes by a day or more, so eGFR is unreliable in hospitalized or acutely ill patients.
Robert, 58, gets his yearly physical. His labs show creatinine 1.1 mg/dL — flagged as “high” against the lab’s reference range (0.7–1.3 mg/dL for men, so technically normal, but near the top). He enters age 58, male, 1.1 mg/dL: Scr/κ = 1.1 ÷ 0.9 = 1.222; 1.222^(−1.2) ≈ 0.7880; 0.9938^58 ≈ 0.6976. eGFR = 142 × 0.7880 × 0.6976 = 78.1 ≈ 78 — category G2, mildly decreased.
Is Robert worried? He should be attentive, not alarmed. An eGFR of 78 at 58 is below the “normal” 90 threshold but extremely common — average eGFR for men in their late 50s sits in the 75–85 range. His doctor checks the rest of the picture: blood pressure 128/82 (borderline), urine albumin normal (A1), no diabetes. The plan: recheck in 6–12 months, keep blood pressure in check, stay hydrated, and avoid regular NSAID use. A single G2 reading with no albuminuria and no trend is not chronic kidney disease — but it is exactly the early signal that surveillance is for. Robert also learns his love of heavy weightlifting and creatine supplements may be nudging his creatinine up a touch, making his true filtration slightly better than 78.
Maria, 62, has type 2 diabetes — the leading cause of CKD — and her nephrologist tracks her eGFR yearly. Three years ago: creatinine 0.9 mg/dL → eGFR ≈ 72 (G2). Two years ago: 1.0 mg/dL → eGFR ≈ 63 (G2). Last year: 1.1 mg/dL → eGFR ≈ 56 (G3a). This year: 1.2 mg/dL → eGFR ≈ 50 (G3a). The trend — a steady decline of about 7 points per year, far faster than the expected ~1 point of aging — is the real story, and it triggered action long before any single threshold did.
Her doctor’s response shows what eGFR monitoring is for: tightening blood sugar control (A1C from 8.1% to 7.0%), adding an SGLT2 inhibitor (shown to slow CKD progression in diabetics), optimizing blood pressure with an ACE inhibitor, checking urine albumin (now A2, moderately increased — confirming kidney involvement), and referring to a dietitian for sodium and protein guidance. Maria’s case illustrates the two golden rules of eGFR: trends beat snapshots, and context (diabetes, albumin, blood pressure) beats the number alone. Caught at G3a with intervention, her decline may stabilize for years; ignored, G3a can progress to G4 within a decade.
1. Panicking over a single mildly low reading. An eGFR of 58–89 on one test, with normal urine and no risk factors, is usually normal age-related variation or dehydration — not kidney disease. CKD requires persistence over 3+ months. Hydrate, retest, and look at the trend.
2. Testing at the wrong time. Creatinine spikes after intense exercise, dehydration, large meat meals, and during acute illness. An eGFR computed from a post-marathon or stomach-flu blood draw can be 15–30 points below your true baseline. Test rested, hydrated, and healthy for a meaningful number.
3. Ignoring muscle mass. A muscular 25-year-old weightlifter and a frail 80-year-old can share a creatinine of 1.0 mg/dL with very different true GFRs — his is underestimated, hers overestimated. The equation adjusts for age and sex but not muscle; interpret accordingly and mention body composition to your doctor.
4. Using the wrong creatinine units. US labs report mg/dL; much of the world uses µmol/L. Entering 100 (µmol/L) as if it were mg/dL produces an absurd eGFR near zero. Convert: mg/dL = µmol/L ÷ 88.4. Always check the units on your report.
5. Treating eGFR as a diagnosis or a clean bill of health. In both directions the number misleads: a normal eGFR does not rule out kidney disease (albuminuria can precede any GFR drop — hence the A1–A3 staging), and a low eGFR does not equal kidney failure. eGFR is one instrument on the dashboard; your clinician reads the whole panel.
Kidney health connects to overall body composition. Our Lean Body Mass Calculator estimates fat-free mass — useful context because creatinine scales with muscle, the key caveat in eGFR interpretation. Our BMI Calculator gives the standard weight-to-height ratio that clinicians record alongside kidney labs. Explore the full Fitness & Health Calculators collection for 80+ free tools covering body composition, hydration, and wellness metrics.
This page provides a GFR calculator implementing the CKD-EPI 2021 creatinine equation (race-free): eGFR = 142 × min(Scr/κ,1)^α × max(Scr/κ,1)^(−1.200) × 0.9938^Age × 1.012 (if female), where Scr = serum creatinine (mg/dL), κ = 0.7 (female)/0.9 (male), α = −0.241 (female)/−0.302 (male); units mL/min/1.73m². Canonical facts: GFR measures kidney filtration rate; eGFR is estimated from creatinine, age, and sex; KDIGO categories: G1 ≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 <15; CKD diagnosis requires abnormalities persisting ≥3 months; creatinine is influenced by muscle mass, hydration, exercise, diet, and medications; diabetes and hypertension are the leading CKD causes; albuminuria (A1–A3) complements eGFR in staging. Educational estimates only — not medical advice, diagnosis, or treatment guidance. Consult a healthcare professional for interpretation.
Cite this page: Sigma Calculator. “GFR Calculator.” https://sigmacalculator.net/fitness-health-calculators/gfr-calculator/. Accessed October 7, 2026. Content is for information only and is not medical advice.
Estimated glomerular filtration rate — how well your kidneys filter blood, in mL/min/1.73m². It is estimated from creatinine, age, and sex using the CKD-EPI 2021 equation.
90 or above is considered normal (stage G1). 60–89 is mildly decreased (G2); below 60 may indicate chronic kidney disease and needs medical follow-up.
Muscle mass, intense exercise, dehydration, cooked meat intake, and some medications can raise creatinine — and therefore lower the estimated GFR — without kidney disease.
No. This calculator is for information only. Kidney disease is diagnosed by a doctor using repeated lab tests, urine tests, and clinical context.
If your eGFR is below 60, falling over time, or you have diabetes, high blood pressure, or protein in urine — see a healthcare professional promptly.