eGFR Calculator (CKD-EPI 2021)
Use this tool to estimate kidney function from serum creatinine, age, and sex.
What is eGFR?
eGFR stands for estimated glomerular filtration rate. It’s a commonly used measure of how well your kidneys are filtering blood. Instead of directly measuring kidney filtration in a specialized test, clinicians estimate it using routine lab values, especially serum creatinine, plus age and sex.
eGFR is reported in mL/min/1.73 m², which standardizes kidney function to a typical body surface area. Doctors use eGFR to screen for chronic kidney disease (CKD), monitor trends over time, guide medication dosing, and decide when further evaluation is needed.
How this eGFR calculator works
This page uses the 2021 CKD-EPI creatinine equation, a widely accepted method for adult kidney function estimation that does not include race. The formula uses:
- Age in years
- Sex assigned at birth
- Serum creatinine (mg/dL or µmol/L)
The calculator first converts creatinine to mg/dL if needed, then computes eGFR and provides a kidney function category.
Interpreting your result
Common GFR categories
- G1: 90 or higher (normal/high)
- 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: below 15 (kidney failure range)
A single low eGFR does not always mean chronic kidney disease. CKD usually requires persistent abnormalities for at least 3 months or evidence of kidney damage (such as elevated urine albumin).
Why eGFR can change
eGFR can fluctuate for many reasons, including both kidney and non-kidney factors:
- Hydration status (dehydration can lower estimated function)
- Recent illness, infection, or hospitalization
- Medication effects (e.g., NSAIDs, ACE inhibitors, diuretics)
- Muscle mass and diet (creatinine production varies by person)
- Lab variation and timing of blood draw
This is why clinicians often focus on trends and repeat testing rather than one isolated number.
When to follow up with a clinician
You should discuss your results with a healthcare professional, especially if:
- Your eGFR is below 60
- Your eGFR is dropping over time
- You have diabetes, hypertension, cardiovascular disease, or a family history of kidney disease
- You notice swelling, foamy urine, blood in urine, fatigue, or changes in urination
Frequently asked questions
Is this calculator for children?
No. This equation is intended for adults. Pediatric kidney function is estimated with different formulas.
Can I use this for medication dosing?
Not by itself. Some drugs use eGFR; others use creatinine clearance or specific clinical criteria. Medication decisions should always be clinician-guided.
What if my result seems unexpectedly low or high?
Recheck units, repeat the test if advised, and review medications and hydration. A clinician can determine whether further tests (e.g., cystatin C, urine albumin, renal imaging) are needed.
Bottom line
An eGFR calculator is a practical first step for understanding kidney function, but it works best as part of a complete clinical picture. Use the number to start informed conversations with your healthcare team—not to self-diagnose.