Estimate Kidney Function
Use this calculator to estimate GFR (glomerular filtration rate) or creatinine clearance from common clinical formulas.
Educational tool only. Not a diagnosis. Always confirm with a licensed clinician.
What is GFR?
GFR (glomerular filtration rate) is an estimate of how well your kidneys filter blood. Clinicians often use eGFR (estimated GFR) from blood creatinine, age, and sex to screen for chronic kidney disease (CKD), follow trends over time, and support medication decisions.
A single eGFR value is useful, but trends are even more important. A stable eGFR over months may mean something different than a rapid decline over weeks.
Formulas included in this calculator
1) CKD-EPI 2021 (Creatinine)
This is widely used for adult kidney function estimation and removes race from the equation. It reports eGFR in mL/min/1.73m².
- Good for routine adult eGFR reporting.
- Uses age, sex, and serum creatinine.
- Often preferred over older MDRD in many settings.
2) MDRD (4-variable)
MDRD is an older equation that still appears in historical charts and legacy systems. It can be useful for comparison with prior records, but many clinicians now favor CKD-EPI equations.
3) Cockcroft-Gault
Cockcroft-Gault estimates creatinine clearance (CrCl) in mL/min and includes body weight. It is still commonly referenced in medication dosing resources.
- Reports CrCl (not exactly the same as eGFR).
- If height is provided, this page also shows an indexed value to 1.73m².
How to use this formula GFR calculator
- Select the formula you want to use.
- Enter age, sex, and serum creatinine.
- Choose the correct creatinine unit (mg/dL or µmol/L).
- If using Cockcroft-Gault, add body weight (and optionally height).
- Click Calculate to view your result and CKD stage interpretation (when applicable).
CKD staging reference (by eGFR)
- G1: ≥ 90 (normal or high, with other evidence of kidney damage if CKD 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 limitations
No formula is perfect. Results may be less reliable in:
- Acute kidney injury (rapidly changing creatinine)
- Pregnancy
- Very high or very low muscle mass
- Amputation, cachexia, or extreme body composition
- Children (pediatric equations are different)
Use lab trends, urinalysis, albumin-to-creatinine ratio, blood pressure, imaging, and clinical context for full assessment.
FAQ
Is eGFR the same as creatinine clearance?
Not exactly. eGFR is normalized to body surface area (1.73m²), while Cockcroft-Gault estimates CrCl in mL/min. They are related but not interchangeable in every clinical scenario.
Which formula should I choose?
For most adults, CKD-EPI 2021 is commonly preferred for eGFR reporting. For some drug dosing references, Cockcroft-Gault may still be explicitly requested.
Can I diagnose CKD from one number?
Usually no. CKD diagnosis generally requires persistent findings over at least 3 months and/or other signs of kidney damage.
Bottom line
A formula GFR calculator is a practical way to estimate kidney function quickly. Use it as a screening and decision-support tool, then confirm interpretation with your healthcare professional—especially if results are low, rapidly changing, or clinically unexpected.