Free gfr calculator
Estimate your kidney function in two seconds. Enter your serum creatinine, age, and sex, and the calculator returns your eGFR using the race-free CKD-EPI 2021 equation, plus the CKD stage it falls in (G1 to G5) — updated live, as you type.
On this page14 sections
CKD-EPI 2021 (race-neutral) equation. For medical use only — results must be interpreted by a qualified healthcare provider.
Results are estimates. Consult a professional.
What is eGFR, and what does it measure?
Your eGFR — estimated glomerular filtration rate — is the single best number for how well your kidneys are filtering. Glomeruli are the millions of tiny filters in your kidneys; the glomerular filtration rate is the volume of blood they clean each minute, reported as millilitres per minute per 1.73 m² of body surface area (mL/min/1.73 m²). Healthy adult kidneys filter roughly 90–120 mL a minute. This GFR calculator estimates that rate from a single blood test result.
True GFR can only be measured directly with a complex tracer test that is rarely done in routine care. Instead, labs estimate it — the 'e' in eGFR — from your blood creatinine level together with your age and sex. The estimate is accurate enough to screen for kidney disease, stage it, and track it over time, which is why eGFR is reported on almost every standard blood panel.
How the CKD-EPI 2021 equation works
This calculator uses the CKD-EPI 2021 creatinine equation — the current US standard, published by Inker and colleagues and recommended by the National Kidney Foundation and the American Society of Nephrology. Its headline change from older formulas is that it is race-free: the 2021 equation removed the race coefficient that earlier CKD-EPI and MDRD equations applied to Black patients, so everyone is now estimated on one scale.
In plain terms, the equation takes your creatinine and compares it to a sex-specific breakpoint (κ), applies a steeper penalty once creatinine rises above that breakpoint (the −1.200 exponent), then nudges the result down a little for every year of age and up slightly for females. The calculator above runs the exact formula — you enter your serum creatinine, age, and sex, and it returns your eGFR and the CKD stage it falls in.
A worked example using the GFR calculator
Robert is a 55-year-old man. His routine blood test comes back with a serum creatinine of 1.3 mg/dL — slightly above the usual reference range — and he wants to know what that means for his kidneys. Here is exactly how the calculator works it out.
Step 1 — Set the male constants
For a male, κ = 0.9 and α = −0.302. His creatinine (1.3) divided by κ is 1.3 ÷ 0.9 = 1.444, which is above 1 — so the steeper max(…, 1)^−1.200 branch does the work and the min(…, 1) branch equals 1.
Step 2 — Apply the creatinine and age terms
The creatinine term is 1.444^−1.200 ≈ 0.643. The age term is 0.9938^55 ≈ 0.710. There is no female multiplier, so that factor is 1.
Step 3 — Multiply it out
142 × 0.643 × 0.711 ≈ 65 mL/min/1.73 m². That eGFR lands in the G2 band (60–89) — mildly reduced filtration.
CKD stages by eGFR: G1 to G5
Kidney function is staged by eGFR using the international KDIGO system, from G1 (normal) down to G5 (kidney failure). The table below is the exact set of bands this calculator uses. Note the crucial caveat on the first two rows: an eGFR at or above 60 is only classified as chronic kidney disease if there is a separate sign of kidney damage — without that, a result of 60+ is considered normal kidney function.
| Stage | eGFR (mL/min/1.73 m²) | What it means |
|---|---|---|
| G1 | 90 or higher | Normal filtration — CKD only if a damage marker is present |
| G2 | 60 – 89 | Mildly reduced — CKD only if a damage marker is present |
| G3a | 45 – 59 | Mild to moderate reduction |
| G3b | 30 – 44 | Moderate to severe reduction |
| G4 | 15 – 29 | Severely reduced filtration |
| G5 | Less than 15 | Kidney failure (end-stage); dialysis or transplant often needed |
Source: KDIGO CKD GFR (G) categories, as published by the National Kidney Foundation. G1/G2 require a marker of kidney damage (e.g. albuminuria) to be classed as CKD.
What affects your eGFR: creatinine, age, and sex
Only three things feed the CKD-EPI 2021 equation, and understanding each makes the result make sense.
Because creatinine comes from muscle, things unrelated to your kidneys can shift it — and therefore your eGFR. A large, very muscular person or someone who has just done heavy exercise or eaten a lot of cooked meat can read a higher creatinine (lower eGFR) than their kidneys warrant; someone with low muscle mass can read the opposite. Dehydration and certain medications can also temporarily move the number. This is why a single result is interpreted in context, not in isolation.
eGFR vs creatinine — what's the difference?
Both appear on the same blood report and move together, which causes confusion. They are two views of the same thing: creatinine is the raw measurement, and eGFR is what that measurement implies about your filtering rate once age and sex are accounted for.
The key difference is that they move in opposite directions. A high creatinine means waste is building up, which signals low filtration — so a high creatinine produces a low eGFR. eGFR is usually the more useful number for patients because it folds age and sex into one figure you can compare against the staging table, whereas a raw creatinine of, say, 1.3 mg/dL means very different things for a 30-year-old man and a 75-year-old woman.
What is a normal eGFR — and is 60 bad?
A normal eGFR is 90 or above in a healthy adult, and a result of 60 or higher is generally considered normal kidney function as long as there is no other sign of kidney damage. It is also normal for eGFR to drift down with age: filtration falls roughly 1 mL/min per year after about age 30–40, so a value in the 60s or 70s in an older adult often reflects ordinary aging rather than disease.
Is an eGFR of 60 'bad'? Not by itself — 60 sits right at the top of the G2 band and means your kidneys are filtering at roughly 60% of the young-adult benchmark. What matters is the trend and whether it stays there. A result that is consistently below 60 for three months or more is the definition of chronic kidney disease and warrants follow-up, while a one-off dip can be caused by something temporary like dehydration.
What does a low eGFR mean?
A low eGFR means your kidneys are filtering more slowly than expected for your age and sex. It is a signal to investigate, not an automatic diagnosis — and the most common explanations are not all serious.
- Chronic kidney disease. A persistently low eGFR (under 60 for three or more months) is the leading reason and the one staging is built around.
- A temporary dip. Dehydration, certain medications (including some painkillers), or a recent illness can lower eGFR briefly, and it recovers once the cause is fixed.
- Acute kidney injury. A sudden, sharp drop over hours or days — often during a serious illness — which is a medical situation distinct from slow, chronic decline.
- Normal aging. A modestly reduced eGFR in an older adult, with no other signs of damage, is frequently just the kidneys aging.
The two leading causes of lasting kidney damage are high blood pressure and diabetes, both of which harm the tiny filters over time. That is why a low eGFR is usually followed up with a urine test for protein (albuminuria) and a check of your blood pressure and blood sugar — the eGFR number alone does not tell the whole story.
When to see a doctor about your eGFR
This calculator helps you understand a result, but it cannot examine you or decide what your number means for your health. Share any eGFR result with a clinician, and treat the following as prompts to follow up rather than self-diagnose.
- An eGFR below 60. Especially if it is new or has dropped from a previous result — your doctor will usually repeat the test and check for protein in your urine.
- A falling trend. A steady decline across several tests matters more than any single value; a declining eGFR is the main sign that kidney disease is progressing.
- An eGFR under 30. This is moderate-to-severe reduction (G4 and below) and normally means referral to a kidney specialist (nephrologist).
- Warning symptoms. Swelling in the legs or face, foamy urine, marked changes in how much you urinate, persistent fatigue, or nausea alongside a low eGFR all warrant prompt medical attention.
Data sources and methodology
This calculator uses the 2021 CKD-EPI creatinine equation (Inker LA et al., New Approaches to the Estimation of GFR, N Engl J Med 2021), the race-free formula recommended by the National Kidney Foundation and the American Society of Nephrology. The CKD stage bands (G1–G5) follow the KDIGO clinical practice guideline as published by the National Kidney Foundation. eGFR is computed exactly from the published coefficients and rounded for display. Pair this with the blood pressure, A1c, and BMI calculators, since blood pressure and diabetes are the leading drivers of kidney damage.
National Kidney Foundation — eGFR calculator and CKD-EPI 2021 creatinine equation.Frequently asked questions about the free gfr calculator
About this GFR calculator
This GFR calculator runs entirely in your browser. The creatinine, age, and sex you enter never leave your device — nothing is sent to a server, logged, or shared. It applies the race-free CKD-EPI 2021 creatinine equation exactly as published by the National Kidney Foundation, then matches your eGFR to the KDIGO CKD stage bands (G1 to G5), updating instantly as you type.
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