Use this free eGFR calculator to estimate kidney function using the CKD-EPI 2021 creatinine equation (adult use). Enter your lab values below and click Calculate.
Result is an estimate and should be interpreted by a qualified clinician with your full history, repeated labs, and urine testing.
What is GFR and why does it matter?
GFR stands for glomerular filtration rate. It describes how well your kidneys filter blood each minute. Because direct measurement is difficult, most clinics use an estimated value called eGFR based on blood creatinine, age, and sex.
A lower eGFR can indicate reduced kidney function, but one single number does not diagnose chronic kidney disease (CKD) by itself. Clinicians usually combine:
- Repeated eGFR values over at least 3 months
- Urine albumin-to-creatinine ratio (ACR)
- Blood pressure, diabetes status, medications, and symptoms
- Imaging and additional blood tests when appropriate
How this kidney function calculator works
This page uses the CKD-EPI 2021 creatinine equation for adults. It does not use a race coefficient. The estimate is normalized to a body surface area of 1.73 m² and reported as:
mL/min/1.73 m²
If you enter height and weight, the calculator also provides an approximate absolute GFR (mL/min) using Mosteller body surface area adjustment.
Quick interpretation of GFR categories
| Category | eGFR (mL/min/1.73 m²) | General Meaning |
|---|---|---|
| G1 | ≥ 90 | Normal or high (if no kidney damage markers) |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mild to moderate decrease |
| G3b | 30–44 | Moderate to severe decrease |
| G4 | 15–29 | Severely decreased |
| G5 | < 15 | Kidney failure range |
Understanding ACR with eGFR
The urine albumin-to-creatinine ratio (ACR) is a key companion test. A normal or near-normal eGFR can still hide early kidney damage if albumin is elevated.
- A1: < 30 mg/g (normal to mildly increased)
- A2: 30–300 mg/g (moderately increased)
- A3: > 300 mg/g (severely increased)
In clinical practice, eGFR category and ACR category are combined to estimate progression and cardiovascular risk.
When a GFR estimate can be less accurate
Creatinine-based formulas are useful, but not perfect. Results may be less accurate in people with:
- Very high or very low muscle mass
- Recent severe illness, dehydration, or acute kidney injury
- Unusual diet patterns (very high meat intake before test)
- Pregnancy
- Age under 18 (pediatric formulas are different)
If creatinine-based eGFR seems inconsistent with clinical findings, providers may order cystatin C or a combined creatinine-cystatin equation for a more precise estimate.
How to use this calculator correctly
Step-by-step
- Enter your age in years.
- Select sex at birth (required by current equation structure).
- Enter serum creatinine from your lab report.
- Choose the same unit shown on your report (mg/dL or µmol/L).
- Optionally add urine ACR, height, and weight for extended interpretation.
- Click Calculate eGFR.
For personal tracking, use the same lab and similar testing conditions when possible to reduce variation.
Frequently asked questions
Is one low eGFR result enough to diagnose CKD?
Usually no. CKD generally requires abnormalities present for at least 3 months. Your clinician will often repeat testing.
Can eGFR improve?
Sometimes, yes. Better blood pressure control, diabetes management, hydration balance, medication adjustments, and avoiding nephrotoxic exposures can stabilize or improve numbers in some people.
What should I do if my eGFR is below 60?
Schedule a follow-up with your clinician. Ask for repeat creatinine, urine ACR, blood pressure review, and medication review (including over-the-counter drugs like NSAIDs).
Bottom line
A GFR kidney function calculator is a useful starting point for understanding kidney health. The most meaningful interpretation comes from trends over time and full clinical context. Use this tool for education and discussion, not self-diagnosis.