This GFR calculator estimates glomerular filtration rate (eGFR) from serum creatinine using the current CKD-EPI 2021 equation — the race-free formula labs now use — with the CKD stage ranges doctors interpret it against. It is an educational estimate; kidney health decisions belong with your clinician and your actual lab report.

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The CKD-EPI 2021 Equation

eGFR = 142 × min(Scr/κ, 1)α × max(Scr/κ, 1)−1.200 × 0.9938Age (× 1.012 for women), where κ is 0.7 (women) or 0.9 (men) and α is −0.241 or −0.302. The 2021 refit removed the race coefficient from the 2009 version — one equation for everyone, which this calculator implements exactly. Creatinine comes from muscle metabolism, so the equation converts a waste-product concentration into an estimated filtration rate, normalized to a standard body surface (mL/min/1.73 m²). Part of our Health Calculators collection.

Worked Example (Verified)

  • Man, age 40, creatinine 1.0 mg/dL: ratio = 1.0/0.9 = 1.111 → 142 × 1 × 1.111−1.2 × 0.993840 = eGFR ≈ 98 — comfortably in the G1 band
  • Woman, age 65, creatinine 1.0: κ 0.7 changes everything — ratio 1.43, and age's 0.9938⁶⁵ ≈ 0.67 — eGFR lands at ≈ 63 (G2 band) at the same creatinine value that gave the 40-year-old man 98. Creatinine alone, without age and sex, is half a story — precisely why eGFR exists.

Reading eGFR Like a Clinician (Briefly)

  • Stages: G1 ≥90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 <15 — but CKD requires persistence (≥3 months) and staging also uses urine albumin (A1–A3). A single number is a screening signal, not a diagnosis.
  • Trends beat points: a stable 58 for years and a fall from 95 to 58 in a year are entirely different clinical stories with the same printout.
  • Creatinine is muscle-biased: bodybuilders read "worse," the frail or amputees read "better," independent of true kidney function; cystatin C-based eGFR exists for those cases.
  • eGFR declines naturally ~0.5–1 point/year after 40 — the equation's 0.9938^Age term is that biology, formalized.

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Frequently Asked Questions

What is a normal GFR?

Young healthy adults sit around 90–120 mL/min/1.73 m²; the range drifts down with age. Sustained values under 60 (for 3+ months) meet the filtration criterion for chronic kidney disease and warrant clinician follow-up.

How is eGFR calculated from creatinine?

With the CKD-EPI 2021 equation: 142 × min(Scr/κ,1)^α × max(Scr/κ,1)^−1.200 × 0.9938^age (×1.012 if female), κ and α set by sex. This calculator implements that formula directly.

Why does my lab's eGFR differ slightly from calculators?

Older labs used CKD-EPI 2009 or MDRD equations, and some report the combined creatinine–cystatin C 2021 estimate when both markers are measured. Small differences between equations are normal; trends within one method are what matter.

Can eGFR be wrong?

It is an estimate by design — extreme muscle mass, creatine supplements, certain medications (e.g., trimethoprim), pregnancy and acute illness all bend creatinine away from true filtration. That's why kidney assessment pairs eGFR with urine albumin and repeat testing.

What creatinine level is concerning?

There is no single number — 1.0 mg/dL yields eGFR ≈ 98 for a 40-year-old man but ≈ 63 for a 65-year-old woman (worked above), and higher creatinines diverge further. Interpretation always runs through age, sex, baseline and trend.

Is this GFR calculator free?

Yes — free and educational. It does not diagnose; bring real results to your clinician.