GFR Calculator - Kidney Function eGFR
Use this GFR (Glomerular Filtration Rate) calculator to estimate your kidney function using the CKD-EPI 2021 equation (race-free). Enter your serum creatinine, age, and gender to determine your eGFR and chronic kidney disease (CKD) stage.
How to Use
- Enter your serum creatinine level in mg/dL (from a recent blood test).
- Enter your age in years.
- Select your gender — Male or Female (the equation uses different coefficients).
- Check African American if applicable for the older adjustment factor.
- Click "Calculate eGFR" to see your estimated glomerular filtration rate and CKD stage.
Formula / Method
CKD-EPI 2021 Equation (Race-Free):
Female: eGFR = 142 × (Scr/0.7)α × 0.9938age
Male: eGFR = 142 × (Scr/0.9)α × 0.9938age
Where:
- If Scr ≤ 0.7 (female): α = -0.241; if Scr > 0.7: α = -0.241 × (Scr/0.7)-1.200
- If Scr ≤ 0.9 (male): α = -0.302; if Scr > 0.9: α = -0.302 × (Scr/0.9)-1.200
- Scr = Serum creatinine (mg/dL)
- Results are in mL/min/1.73 m2
The CKD-EPI 2021 equation removes the race coefficient, making it more equitable. It is the current standard for estimating GFR in clinical practice.
CKD Stages Reference
| eGFR (mL/min/1.73m2) | CKD Stage | Kidney Function | Management |
|---|---|---|---|
| ≥ 90 | Normal or Stage 1 | Normal function | Monitor; manage risk factors. |
| 60 - 89 | Stage 2 | Mildly reduced | Yearly monitoring; manage comorbidities. |
| 45 - 59 | Stage 3a | Moderately reduced | Monitor every 6 months; nephrology referral. |
| 30 - 44 | Stage 3b | Moderately to severely reduced | Nephrology follow-up every 3-6 months. |
| 15 - 29 | Stage 4 | Severely reduced | Prepare for dialysis or transplant. |
| < 15 | Stage 5 | Kidney failure | Dialysis or transplant evaluation. |
Examples
A 45-year-old female has serum creatinine of 1.0 mg/dL. Since 1.0 > 0.7: α = -0.241 × (1.0/0.7)-1.200 = -0.241 × 0.674 = -0.162. eGFR = 142 × (1.0/0.7)-0.162 × 0.993845 = 142 × 0.945 × 0.753 = 101 mL/min/1.73m2. This indicates normal kidney function (Stage 1).
Frequently Asked Questions
What is a normal GFR?
A normal GFR is typically 90 mL/min/1.73m2 or higher. However, GFR naturally decreases with age — a healthy 70-year-old may have a GFR of 75 without having kidney disease. GFR of 60 or above is generally considered normal if there is no other sign of kidney damage (like protein in urine). GFR below 60 for 3 months or more indicates chronic kidney disease. Only your doctor can interpret what is normal for you based on your overall health.
What does GFR 60 mean?
A GFR of 60 mL/min/1.73m2 indicates Stage 3a chronic kidney disease (CKD), meaning moderately reduced kidney function. At this level, about 60% of your kidney function remains. Many people with Stage 3a CKD feel fine and may not have obvious symptoms. However, it is important to monitor kidney function regularly, manage blood pressure, control blood sugar, and avoid medications that can further harm the kidneys (like NSAIDs). Your doctor will typically recommend follow-up testing every 6 months.
How is GFR calculated?
GFR cannot be measured directly in routine practice. Instead, it is estimated (eGFR) using equations based on serum creatinine levels, age, gender, and other factors. The CKD-EPI 2021 equation is the current standard. It uses the serum creatinine value, applies different coefficients for males and females, and adjusts for age (kidney function declines with age). The result is expressed in mL/min/1.73m2 (normalized to body surface area). The older MDRD equation is still used in some labs but is less accurate at higher GFR levels.
What factors can affect GFR results?
Several factors can influence eGFR results including: recent high-protein or large meat meals, intense exercise (increases creatinine), dehydration, certain medications (NSAIDs, ACE inhibitors, some antibiotics), pregnancy, and muscle mass. Very muscular individuals may have higher creatinine without kidney disease, while those with low muscle mass (elderly, malnourished) may have falsely low creatinine. Cystatin C-based eGFR can provide a more accurate assessment when creatinine-based results are uncertain.