AI Health Assistant
BetaAsk questions about your calculation results
3 free questions per session
AI provides general information, not medical advice. Always consult a healthcare professional.
About This Calculator
Glomerular filtration rate measures how effectively your kidneys filter waste from the blood and is the primary indicator of kidney function. This calculator estimates GFR using the CKD-EPI or MDRD equations with serum creatinine levels, age, sex, and race. Doctors use GFR results to stage chronic kidney disease, adjust medication dosages, and determine when dialysis or transplant evaluation may be necessary.
Quick Tips
- 1 GFR below 60 for three months indicates chronic kidney disease.
- 2 Stay hydrated before blood tests — dehydration temporarily lowers GFR readings.
- 3 High-protein diets can artificially elevate creatinine and lower GFR results.
Example Calculation
A 55-year-old male, serum creatinine 1.4 mg/dL (CKD-EPI 2021).
eGFR: 56 mL/min/1.73m2 | CKD Stage: 3a (mild-moderate) | Normal: >90
What is GFR?
Glomerular Filtration Rate (GFR) measures how well your kidneys filter waste from the blood. It is considered the best overall indicator of kidney function. A normal GFR is approximately 90-120 mL/min/1.73m². GFR naturally declines with age, decreasing about 1 mL/min per year after age 40.
How eGFR is Calculated
Estimated GFR (eGFR) is calculated using the MDRD (Modification of Diet in Renal Disease) equation: eGFR = 175 × (creatinine)^-1.154 × (age)^-0.203 × 0.742 (if female) × 1.212 (if African American). This formula uses serum creatinine from a simple blood test along with age, sex, and race.
Kidney Function Stages
Stage 1: GFR 90+ (normal function with other signs of kidney damage). Stage 2: GFR 60-89 (mild decrease). Stage 3a: GFR 45-59 (mild to moderate decrease). Stage 3b: GFR 30-44 (moderate to severe decrease). Stage 4: GFR 15-29 (severe decrease). Stage 5: GFR below 15 (kidney failure, dialysis may be needed).
Protecting Your Kidney Health
Maintain healthy blood pressure (below 130/80), control blood sugar if diabetic, stay hydrated, limit NSAID use, avoid excessive protein intake, do not smoke, and maintain a healthy weight. Regular screening is recommended if you have diabetes, high blood pressure, heart disease, or a family history of kidney disease.
Frequently Asked Questions
A normal GFR is 90-120 mL/min/1.73m² for healthy young adults. GFR naturally decreases about 1 mL/min per year after age 40. A GFR above 60 with no other signs of kidney damage is generally considered adequate function. Below 60 for 3 or more months indicates chronic kidney disease.
Creatinine is a waste product produced by muscles. Normal levels are 0.7-1.3 mg/dL for men and 0.6-1.1 mg/dL for women. Higher creatinine suggests reduced kidney function because the kidneys are not filtering it efficiently. However, muscular individuals naturally have higher creatinine levels.
A single low GFR reading does not necessarily indicate kidney disease — dehydration, certain medications, and recent high-protein meals can temporarily affect results. If your GFR is below 60, your doctor will likely repeat the test in 3 months. Persistent low GFR warrants further evaluation.
The race adjustment in the MDRD formula accounts for the observation that African Americans tend to have higher average muscle mass, which produces more creatinine. Some newer formulas (CKD-EPI 2021) have removed the race variable. Discuss the most appropriate formula with your healthcare provider.