eGFR Calculator (CKD-EPI 2021)
Estimate kidney function using age, sex, and serum creatinine. Output is in mL/min/1.73 m².
Educational tool only. This calculator does not diagnose chronic kidney disease. Always interpret results with your clinician and laboratory context.
What is glomerular filtration rate (GFR)?
Glomerular filtration rate is the best overall index of kidney filtering function. It estimates how much blood your kidneys filter each minute. In clinical practice, most reports show an estimated GFR (eGFR) rather than a directly measured GFR, because direct measurement is expensive and time-consuming.
eGFR is typically calculated from a blood test called serum creatinine, together with age and sex. The number helps clinicians detect kidney disease, monitor progression, and guide medication dosing decisions.
How this calculator works
This page uses the CKD-EPI 2021 creatinine equation (race-free). It reports eGFR in mL/min/1.73 m², which is normalized to a standard body surface area.
If you enter height and weight, the tool also estimates body surface area (Du Bois formula) and provides an absolute GFR adjusted to your body size.
How to use the calculator correctly
- Enter your age in years (adults only).
- Select biological sex as used in the CKD-EPI equation.
- Enter serum creatinine from your lab report.
- Pick the correct creatinine unit: mg/dL or µmol/L.
- Optionally add height and weight for absolute GFR.
A unit mistake can significantly change your result, so double-check your laboratory units before calculating.
Interpreting eGFR values
Common GFR categories
- G1: ≥ 90 (normal or high, if no other kidney abnormalities)
- 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: chronic kidney disease (CKD) is diagnosed using more than one number. Doctors combine eGFR trends with urine albumin, imaging, blood pressure, diabetes status, and duration (usually at least 3 months of persistent findings).
Why one reading is not the whole story
Kidney function can fluctuate. Hydration status, recent high-protein meals, intense exercise, acute illness, and some medications may transiently affect creatinine. Because of that, clinicians focus on trends over time and clinical context.
If your eGFR looks unexpectedly low, your clinician may repeat labs, check urine albumin-to-creatinine ratio (uACR), and review medicines that may affect renal function or creatinine secretion.
When eGFR may be less accurate
- Very high or very low muscle mass
- Amputation, neuromuscular disease, or severe malnutrition
- Pregnancy
- Acute kidney injury (rapidly changing creatinine)
- Children and adolescents (different equations required)
In these situations, clinicians may use cystatin C-based equations, combined equations, or direct GFR measurement.
Related kidney function terms
- Serum Creatinine: Blood marker used in most eGFR calculators.
- BUN: Blood urea nitrogen, another kidney-related marker.
- uACR: Urine albumin-to-creatinine ratio; key for CKD risk staging.
- CKD stages: Classification using GFR category and albuminuria category.
- Renal function test: Broad term for blood/urine tests assessing kidney health.
Frequently asked questions
Is a low eGFR always chronic kidney disease?
No. CKD requires persistent abnormality over time and/or additional evidence of kidney damage.
Can eGFR improve?
It can stabilize or improve depending on cause, blood pressure control, glucose management, medication review, and hydration status. Some declines are reversible, others are progressive.
Should I panic if my result is below 60?
Don’t panic—follow up. A single value is not a diagnosis. Repeat testing and urine markers are essential for proper interpretation.
Bottom line
A glomerular filtration rate calculator is a useful way to estimate kidney function quickly. Use it as a screening and educational tool, not as a stand-alone diagnosis. The most meaningful interpretation combines eGFR, urine albumin, symptoms, medical history, and repeat measurements with your healthcare professional.