GFR Calculator (eGFR, CKD-EPI)
Estimate kidney function (eGFR) from creatinine, age and sex, with the CKD stage.
Results update as you type.
About this calculator
A GFR calculator estimates the glomerular filtration rate — how well the kidneys filter blood — from a serum creatinine test, age and sex. It uses the race-free 2021 CKD-EPI creatinine equation, reporting eGFR in mL/min/1.73 m² and the matching chronic kidney disease (CKD) stage from G1 to G5. This is an estimate for education only and does not replace testing or advice from a clinician.
The equation weighs creatinine against a sex-specific constant, then adjusts for age. For a 50-year-old man with a serum creatinine of 1.0 mg/dL, CKD-EPI returns an eGFR of about 92 mL/min/1.73 m², which is stage G1 — normal function. A woman with the same creatinine reads slightly differently because the equation uses a lower constant (0.7 versus 0.9) and a 1.012 sex factor. Enter creatinine in mg/dL or µmol/L and the tool converts.
The result maps to a CKD stage: 90+ is G1, 60–89 G2, 45–59 and 30–44 are G3a and G3b, 15–29 is G4 and below 15 is kidney failure (G5). Stages G3 and worse usually prompt medical follow-up. Because eGFR rests on a single creatinine value and is affected by muscle mass and diet, it is a screening estimate, not a diagnosis — confirm any concern with a clinician.
Frequently asked questions
What is the CKD-EPI equation?
It is the standard formula for estimating GFR from creatinine: eGFR = 142 × min(Scr/κ,1)^α × max(Scr/κ,1)^−1.200 × 0.9938^age × 1.012 (if female), where κ and α depend on sex. The 2021 version removed the race coefficient.
What do the GFR numbers mean?
An eGFR of 90 or above with no other signs is normal; 60–89 is mildly reduced; 45–59 and 30–44 are stages G3a and G3b; 15–29 is severe (G4) and below 15 is kidney failure (G5). Stages G3–G5 usually need medical follow-up.
Is this a diagnosis of kidney disease?
No. eGFR is an estimate that can be affected by muscle mass, diet and a single creatinine reading. Chronic kidney disease is diagnosed by a clinician using repeat tests over time plus urine and other findings.
What is a normal eGFR?
An eGFR of 90 or above with no other signs of kidney damage is considered normal. A 50-year-old man with a creatinine of 1.0 mg/dL comes out at about 92, which is stage G1.
What eGFR counts as stage 3 kidney disease?
Stage G3a is an eGFR of 45–59 and G3b is 30–44, reflecting a moderate loss of filtering capacity. These stages usually prompt monitoring and management by a clinician.
Why does the equation lower eGFR as I age?
Filtration naturally declines over the years, so CKD-EPI includes an age term (0.9938 raised to your age). A modestly reduced eGFR in an older adult is not automatically kidney disease.
What makes serum creatinine go up or down?
Higher muscle mass, meat-heavy meals and dehydration raise creatinine and so lower the estimated GFR, while low muscle mass lowers it. Since eGFR hinges on that single value, repeat testing is needed to interpret it properly.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/gfr/curl
curl "https://calculator.free/api/v1/gfr/?age=50&sex=male&creatinine=1.0&units=mgdl"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/gfr/?" + new URLSearchParams({
"age": "50",
"sex": "male",
"creatinine": "1.0",
"units": "mgdl"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.