GFR Calculator — estimate kidney function (CKD-EPI 2021)

This is an estimate, not a medical diagnosis. eGFR is one part of assessing kidney health, and a single value can be affected by muscle mass, diet, hydration and lab methods. It is for adults (18+) — children use a different equation (such as the CKiD "U25" or Schwartz formula). Do not start, stop or change any treatment based on it — discuss any result with your doctor.

How it works

GFR (glomerular filtration rate) is the volume of blood your kidneys filter per minute, the main measure of kidney function. It's hard to measure directly, so it is estimated (eGFR) from a blood creatinine level — a waste product kidneys clear — adjusted for age and sex. This calculator uses the 2021 CKD-EPI creatinine equation, the current race-free standard recommended by the National Kidney Foundation and the American Society of Nephrology:

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 (mg/dL), κ is 0.7 (female) or 0.9 (male), and α is −0.241 (female) or −0.302 (male). Higher creatinine or older age lowers eGFR. Results are in mL/min/1.73 m². (If your lab reports creatinine in µmol/L, divide by 88.4 to get mg/dL.)

An eGFR of 90 or above is generally normal; 60–89 is mildly reduced; below 60 for three months or more may indicate chronic kidney disease, and the lower the number, the more advanced the stage. Staging also considers other findings, which is why it's a clinician's call.

Worked example

A 50-year-old man, serum creatinine 1.0 mg/dL:

• κ = 0.9, α = −0.302; Scr/κ = 1.11
• eGFR = 142 × 1 × 1.11^−1.200 × 0.9938^50 ≈ 92 mL/min/1.73 m² — normal

Frequently asked questions

What is a normal eGFR?

Roughly **90 or higher** is normal for most adults; it declines gradually with age. **60–89** is mildly reduced and often still normal for older adults, while a value **under 60 that persists** for three months suggests chronic kidney disease.

What do the GFR stages (G1–G5) mean?

KDIGO groups eGFR into categories: **G1** ≥90 (normal or high), **G2** 60–89 (mildly decreased), **G3a** 45–59, **G3b** 30–44, **G4** 15–29 (severely decreased), and **G5** below 15 (kidney failure). G1 and G2 are only considered kidney disease when there are other signs of kidney damage, such as protein in the urine — which is why staging is a clinician's judgment, not a number alone.

Why does the 2021 equation remove race?

The older CKD-EPI equation included a race coefficient; in 2021 the NKF and ASN recommended a **race-free** equation to avoid race-based differences in care. This calculator uses that version.

What can affect the result?

Creatinine depends on muscle mass, so very muscular or very frail people can have eGFR estimates that are too high or too low. Diet (large meat intake), some medications, hydration and lab calibration can also shift the number.

Is eGFR the same as a kidney diagnosis?

No. It's one estimate. Diagnosing and staging kidney disease also uses urine tests (like albumin), repeat measurements over time, and your overall health — all interpreted by a clinician.

My creatinine is in µmol/L — what do I enter?

Divide the µmol/L value by **88.4** to convert to mg/dL. For example, 88.4 µmol/L = 1.0 mg/dL.