GFR Calculator

This calculator estimates your eGFR (estimated glomerular filtration rate), which is a common way to describe how well your kidneys filter waste from your blood. It's useful if you have a recent creatinine blood test and want a clearer idea of what the number means. The tool can help adults who are tracking kidney health, managing conditions like diabetes or high blood pressure, or simply reviewing lab results. You enter details like age, sex, and serum creatinine. The calculator then provides an estimated GFR result in mL/min/1.73 m², a standard unit used on many lab reports.

How to Use This Calculator

1. Find your serum creatinine value on your lab report.
2. Select the correct unit (mg/dL or µmol/L).
3. Enter your age in years.
4. Choose your sex (as listed on your lab report).
5. Click Calculate to get your estimated GFR (eGFR).
6. Compare results carefully and try to use tests from the same lab when possible.

What This Calculator Measures

This calculator estimates kidney filtration, usually reported as eGFR.

• GFR (Glomerular Filtration Rate): The speed at which your kidneys filter blood.
• eGFR: An estimate of GFR calculated from creatinine and personal details. It's commonly used because directly measuring true GFR is more complex.
• Serum creatinine: A waste product from normal muscle activity. Healthy kidneys remove it from the blood.
• mL/min/1.73 m²: A standardized unit that helps compare results across different body sizes.

Formula or Logic

This tool uses a widely accepted medical equation to estimate kidney filtration using:

• your creatinine level,
• your age,
• and your sex.

In simple terms:

• Higher creatinine often leads to a lower eGFR.
• Older age often lowers the estimate even if creatinine is similar.
• The result is an estimate, not a perfect measurement, but it is very useful for tracking and clinical discussions.

Example Calculations

These examples show how inputs can change the estimate. Exact values may vary depending on the equation used.

Example 1

• Age: 35; Sex: Female; Creatinine: 0.8 mg/dL
• Output: eGFR is typically high/normal for many healthy adults.

Example 2

• Age: 60; Sex: Male; Creatinine: 1.2 mg/dL
• Output: eGFR is typically lower than Example 1, mainly due to higher creatinine and age.

Example 3

• Age: 75; Sex: Female; Creatinine: 1.3 mg/dL
• Output: eGFR is often moderately reduced, and trend tracking becomes especially important.

Understanding Your Results

Your eGFR is a helpful guide, but it is not the full picture.

• A higher eGFR usually suggests better kidney filtration.
• A lower eGFR can suggest reduced kidney function, but short-term factors can affect results too.

Common GFR categories often used in practice:

• G1: ≥90 (normal or high)
• G2: 60–89 (mildly decreased)
• G3a: 45–59 (mildly to moderately decreased)
• G3b: 30–44 (moderately to severely decreased)
• G4: 15–29 (severely decreased)
• G5: <15 (kidney failure)

Important notes:

• A normal eGFR does not always rule out kidney problems. Urine tests can show early kidney damage even when eGFR looks fine.
• One result is not a diagnosis. Repeated results over time usually matter more.
• Clinicians often review eGFR together with urine albumin, blood pressure, and medical history.

Common Mistakes to Avoid

• Entering creatinine in the wrong unit (mg/dL vs µmol/L).
• Using an old lab value that doesn't reflect your current health.
• Comparing results from different labs without noting method differences.
• Treating one low result as a final diagnosis.
• Ignoring urine test findings like albumin or protein.
• Not mentioning medicines or supplements that may affect creatinine.
• Using adult equations for children (pediatric methods are different).
• Interpreting results during illness or dehydration without medical context.

This GFR Calculator estimates eGFR, a common way to describe kidney filtration using creatinine and a few personal details. Use it to better understand your lab report and track trends over time. Remember that one number rarely tells the full story, especially without urine testing and medical context. Try the calculator above to see your results.

Frequently Asked Questions

Common questions about the GFR Calculator are answered below.