Estimated GFR Calculator (CKD-EPI 2021)
Use this tool to estimate kidney filtration rate (eGFR) from serum creatinine, age, and sex. This calculator is intended for adults (18+).
Medical disclaimer: This tool is for education only and does not replace professional diagnosis. Interpret eGFR with urine albumin, history, medications, and clinical context.
What is eGFR?
eGFR stands for estimated glomerular filtration rate. It is a blood test estimate of how well your kidneys filter waste and excess fluid from the bloodstream. The result is typically reported as mL/min/1.73 m² and is one of the most common kidney function markers in clinical practice.
In day-to-day care, clinicians use eGFR to screen for chronic kidney disease (CKD), monitor trends over time, and adjust doses for medications that are cleared through the kidneys. A single value is helpful, but the trend over months is often more important than one isolated number.
How this estimated GFR calculator works
This page uses the 2021 CKD-EPI creatinine equation (race-free). It calculates eGFR from:
- Age
- Sex
- Serum creatinine
If you enter creatinine in µmol/L, the tool converts it to mg/dL automatically before applying the equation.
CKD stage ranges based on eGFR
| GFR Category | eGFR (mL/min/1.73 m²) | General Interpretation |
|---|---|---|
| G1 | ≥ 90 | Normal or high (if other kidney damage markers are present) |
| 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 |
Important context when interpreting results
eGFR is an estimate, not a direct measured filtration value. It can be influenced by muscle mass, diet, hydration, and lab variability. For many people, this estimate is accurate enough for routine care, but interpretation should always include full clinical context.
Why one number is not the full story
- Persistent findings matter: CKD diagnosis typically requires abnormalities present for at least 3 months.
- Urine albumin is essential: Albumin-to-creatinine ratio (uACR) adds critical risk information.
- Medication effects: Some drugs can change creatinine without true kidney injury.
- Body composition: Very low or very high muscle mass can affect creatinine-based formulas.
Common reasons eGFR may decrease
A lower eGFR can occur with many conditions, including diabetes, hypertension, glomerular disease, inherited kidney conditions, dehydration, urinary obstruction, and acute illness. Sometimes a low value is temporary and improves after treatment of the underlying issue.
When to contact a healthcare professional
- Your eGFR is repeatedly below 60.
- Your eGFR drops quickly between tests.
- You have swelling, reduced urine output, blood in urine, or severe fatigue.
- You have diabetes or high blood pressure and have not had recent kidney monitoring.
Tips to support kidney health
- Keep blood pressure in target range.
- Manage blood glucose if you have diabetes.
- Avoid unnecessary NSAID overuse unless advised by your clinician.
- Stay hydrated and maintain regular follow-up labs.
- Discuss all supplements and medications with your care team.
Final note
This estimated GFR calculator is designed for quick educational use and routine awareness. For medical decisions, always use laboratory reports and professional interpretation from your clinician or nephrology team.