Estimated GFR (eGFR) Calculator
Use this adult kidney function calculator to estimate glomerular filtration rate with the CKD-EPI 2021 creatinine equation (race-free).
Medical disclaimer: This tool is educational and not a diagnosis. Always confirm results with your clinician, especially if values are abnormal or symptoms are present.
What is GFR and why does it matter?
GFR stands for glomerular filtration rate. It reflects how much blood your kidneys filter each minute. Because measuring true GFR directly is time-consuming and expensive, clinicians usually use an estimated GFR (eGFR) based on lab markers such as creatinine.
In everyday care, eGFR helps with:
- Screening for chronic kidney disease (CKD)
- Tracking kidney function over time
- Dosing medications that are cleared by the kidneys
- Assessing risk for complications and progression
Which formula does this GFR calculator use?
This calculator uses the CKD-EPI 2021 creatinine equation, the race-free equation adopted by many health systems. It estimates kidney function normalized to a body surface area of 1.73 m2.
The equation incorporates:
- Age
- Sex assigned at birth
- Serum creatinine
While highly useful, creatinine-based eGFR is still an estimate. Muscle mass, diet, acute illness, and lab variation can all influence results.
How to use this eGFR calculator
Step-by-step
- Enter your age (adults 18+ only).
- Select sex assigned at birth.
- Enter serum creatinine and choose the correct unit (mg/dL or µmol/L).
- Optionally enter urine ACR (mg/g) for added CKD risk context.
- Click Calculate eGFR.
The calculator returns your eGFR value, kidney function stage (G category), and—if provided—albuminuria category (A category).
How to interpret your result
eGFR is commonly grouped into CKD G stages:
- G1: ≥ 90 (normal/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)
Important: CKD is usually diagnosed when abnormal kidney findings persist for at least 3 months. A single low eGFR does not always mean chronic kidney disease.
ACR categories (if entered)
- A1: < 30 mg/g (normal to mildly increased)
- A2: 30–300 mg/g (moderately increased)
- A3: > 300 mg/g (severely increased)
Combining G stage and ACR category gives a more complete risk picture than eGFR alone.
Why your calculated GFR may differ from your clinical report
If your clinic’s number differs from this calculator, common reasons include:
- Different equation used (CKD-EPI 2009 vs 2021)
- Different creatinine assay calibration
- Rounding differences in lab software
- Non-steady-state kidney function (rapidly changing labs)
During acute kidney injury, creatinine may lag behind real-time kidney function. In that setting, trend data and clinical judgment are essential.
When to speak with a healthcare professional
Contact a clinician if you have:
- eGFR repeatedly below 60
- Persistent ACR elevation
- Blood in urine, swelling, uncontrolled blood pressure, or fatigue
- Diabetes, hypertension, or family history of kidney disease
Early management can slow progression and reduce cardiovascular risk.
Frequently asked questions
Is eGFR the same as creatinine clearance?
Not exactly. eGFR is an estimate from equations; creatinine clearance may be measured from timed urine collections or estimated with other formulas.
Can hydration change creatinine and eGFR?
Mildly, yes. Severe dehydration can increase creatinine and lower eGFR estimate. Persistent trends are more informative than one isolated result.
Is this calculator for children?
No. Pediatric kidney function is usually estimated with equations such as the bedside Schwartz formula.
Bottom line
A good GFR calculator is useful for quick kidney function screening, but interpretation should always include symptoms, urine findings, blood pressure, and longitudinal trends. Use this tool to support informed conversations with your healthcare team—not to replace them.