What GFR measures
Your kidneys filter your entire blood volume dozens of times a day through roughly a million microscopic filters per kidney. GFR — glomerular filtration rate — is the speed of that filtration, in millilitres per minute. It's the single most-used number for describing how well kidneys work, and the backbone of chronic kidney disease staging.
Measuring true GFR directly is laborious, so medicine estimates it — hence 'eGFR' — from a routine blood value: creatinine, a waste product your muscles release at a steady rate. Healthy kidneys clear it efficiently; struggling kidneys let it accumulate. Feed your creatinine, age, and sex into a validated equation and you get a solid estimate of filtration rate. That's precisely what this calculator does, using the CKD-EPI equation with the older MDRD shown for comparison.
GFR ranges and CKD stages
| Stage | GFR (mL/min/1.73m²) | Meaning |
|---|---|---|
| G1 | ≥ 90 | Normal function |
| G2 | 60–89 | Mildly reduced |
| G3a | 45–59 | Mild to moderate reduction |
| G3b | 30–44 | Moderate to severe reduction |
| G4 | 15–29 | Severely reduced |
| G5 | < 15 | Kidney failure |
Two readings matter more than one: chronic kidney disease is defined by reduced GFR (or other kidney damage markers) persisting for at least three months. GFR also declines gently with normal aging — a 75-year-old at 70 is a very different picture from a 30-year-old at 70.
What an online eGFR can and cannot tell you
The equations are genuinely good, but creatinine-based estimates inherit creatinine's quirks. Muscle mass drives creatinine production, so a bodybuilder's eGFR reads low and a frail elderly person's reads deceptively high. Recent heavy meat meals, creatine supplements, dehydration, and some medications all nudge the number. Clinicians handle borderline cases by repeating the test, checking urine protein, or using cystatin C — none of which a web page can do.
One more piece of honest context: nephrology retired race-based adjustment in 2021, when the CKD-EPI equation was refitted without it. If a result here differs slightly from your lab report, equation versions are the usual reason — your lab's number, interpreted by your doctor, is the one that counts.
Who should actually get tested rather than calculated: anyone with diabetes, high blood pressure, heart disease, or a family history of kidney disease — the conditions responsible for most kidney damage, all of them silent in early stages. A basic metabolic panel at a routine checkup covers it.
Frequently asked questions about GFR
What is GFR?
GFR (glomerular filtration rate) estimates how well your kidneys filter waste from blood. It is a key number in chronic kidney disease staging.
What is a normal GFR?
A GFR of 90 or above is generally normal for healthy adults. Values between 60–89 may need monitoring depending on other factors. Below 60 for three months suggests chronic kidney disease.
Can one GFR reading diagnose kidney disease?
No. Diagnosis requires repeated tests, urine checks, and clinical evaluation. A single online estimate is not enough.
When should I see a doctor about kidney function?
See a provider if you have diabetes, high blood pressure, family history of kidney disease, swelling, or abnormal prior lab results.
Is this medical advice?
No. For kidney function concerns, speak to your doctor or nephrologist.
Sources and further reading
- National Kidney Foundation — About eGFR
- Inker LA et al. — New race-free CKD-EPI equations (NEJM, 2021)
- NIH NIDDK — Kidney disease information
This page is for general information only and is not medical advice or a diagnosis. Kidney function must be assessed by a healthcare professional using laboratory testing.