GFR Calculator - Estimated Glomerular Filtration Rate
Estimate glomerular filtration rate (GFR) from key health inputs to help assess kidney function.
What Is the Estimated Glomerular Filtration Rate (eGFR)?
The estimated glomerular filtration rate (eGFR) is a calculated value that reflects how well your kidneys are filtering waste from your blood. It is derived from the level of creatinine in your blood, along with other factors like age, sex, and body size. This tool uses established formulas to provide an eGFR result, which is a standard clinical measure used to assess kidney function and stage chronic kidney disease (CKD).
How the GFR Calculation Works
This calculator uses the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation, which is the most widely recommended formula for estimating GFR in adults. The equation accounts for:
- Serum Creatinine: A waste product from muscle metabolism that healthy kidneys filter out.
- Age: Kidney function naturally declines with age, so the formula adjusts accordingly.
- Sex: Muscle mass differences between males and females affect creatinine production.
- Race (optional): Some older equations included a race coefficient, but many modern clinical guidelines now recommend using a race-free calculation.
The formula outputs a value in milliliters per minute per 1.73 m² (mL/min/1.73 m²), which normalizes the result for body surface area.
How to Use This GFR Calculator
- Enter your serum creatinine level in the provided unit (mg/dL or µmol/L).
- Input your age.
- Select your sex.
- Choose whether to include the race factor based on your clinical context.
- Click the calculate button to receive your estimated GFR.
The result will display your eGFR value and the corresponding kidney function stage.
Understanding Your GFR Results
Your eGFR result is reported as a number. In general:
- ≥ 90 mL/min/1.73 m²: Normal or high kidney function (Stage 1).
- 60–89 mL/min/1.73 m²: Mildly decreased kidney function (Stage 2).
- 30–59 mL/min/1.73 m²: Moderately decreased kidney function (Stage 3).
- 15–29 mL/min/1.73 m²: Severely decreased kidney function (Stage 4).
- < 15 mL/min/1.73 m²: Kidney failure (Stage 5).
These stages are a clinical guideline. A single eGFR result is not a definitive diagnosis. Your healthcare provider will interpret this value in the context of your overall health, medical history, and other tests.
Common Misconceptions About GFR
- eGFR is not the same as actual GFR. It is an estimate, not a direct measurement. The true GFR can only be measured with a more complex procedure using a tracer substance.
- A single low result does not mean kidney failure. eGFR can fluctuate due to hydration, diet, medication, or acute illness. Persistent low readings over three months are more clinically significant.
- The formula has limitations. It is less accurate in people with very high or very low muscle mass, in pregnant women, and in certain ethnic groups when using older equations.
Practical Use Cases for This Tool
- Routine health screening: To get a baseline assessment of kidney function during a general check-up.
- Monitoring chronic conditions: For individuals with diabetes, hypertension, or a family history of kidney disease to track changes over time.
- Medication dosing guidance: Many drugs are cleared by the kidneys, and knowing your eGFR helps healthcare providers adjust dosages safely.
- Pre-operative assessment: To evaluate kidney function before surgery or procedures that may affect the kidneys.
Limitations of the GFR Calculator
This calculator is a screening and educational tool. It is not a substitute for professional medical advice, diagnosis, or treatment. The following factors can affect the accuracy of the eGFR result:
- Dietary creatinine intake (e.g., high meat consumption or creatine supplements).
- Acute kidney injury or temporary dehydration.
- Certain medications that affect creatinine secretion.
- Pregnancy or conditions that alter body composition.
Always discuss your results with a qualified healthcare professional.
Frequently Asked Questions
What is a normal GFR for my age?
A GFR of 90 mL/min/1.73 m² or higher is generally considered normal. However, GFR naturally decreases with age. For example, a healthy 70-year-old may have a GFR around 60–70 mL/min/1.73 m² without having kidney disease. Your doctor will interpret your result based on your age and overall health.
Is eGFR the same as creatinine clearance?
No. Creatinine clearance is a different test that requires a 24-hour urine collection. eGFR is a calculated estimate based on a single blood test. Both are used to assess kidney function, but eGFR is more commonly used in clinical practice because it is simpler and does not require a urine collection.
Why is the race factor sometimes excluded?
Older GFR equations included a race coefficient because studies showed that Black individuals tended to have higher muscle mass and thus higher creatinine levels. However, this adjustment has been criticized for potentially delaying diagnosis and treatment in Black patients. Many major medical organizations now recommend using a race-free equation to reduce health disparities.
Can I use this calculator if I am pregnant?
The standard eGFR equations are not validated for use during pregnancy. Pregnancy causes significant changes in kidney function and blood volume, making the standard formulas inaccurate. Pregnant individuals should rely on their obstetric provider for kidney function assessment.
How often should I check my GFR?
If you have no known kidney issues and no risk factors, routine screening is not typically needed. If you have diabetes, high blood pressure, or other risk factors, your doctor may recommend checking your eGFR once or twice a year. Follow your healthcare provider's guidance for your specific situation.