How to use the GFR calculator
- Enter your serum creatinine from your blood test report and choose its unit. US labs usually report mg/dL; labs in the UK, Europe, Canada and Australia usually use µmol/L.
- Enter your age. The equation is for adults aged 18 and over.
- Choose your sex, as used for lab reference ranges.
- Read your estimated GFR (eGFR) and its category in the table.
How eGFR is calculated
The calculator uses the 2021 CKD-EPI creatinine equation. The National Kidney Foundation (NKF) and the American Society of Nephrology recommend it for adults in the United States. Unlike the 2009 version, it does not include race.
Creatinine is a waste product from muscle that healthy kidneys filter out of the blood. When filtering slows, creatinine builds up, so a higher creatinine gives a lower eGFR. The equation then allows for age and sex, which affect how much creatinine the body makes. The result is in mL per minute per 1.73 m², the volume of blood filtered each minute, scaled to an average adult body size.
Worked example
The calculator's defaults are a creatinine of 1.0 mg/dL, age 50 and male:
- Scr ÷ κ = 1.0 ÷ 0.9 = 1.111
- min(1.111, 1)^−0.302 = 1, because the value is capped at 1
- max(1.111, 1)−1.200 = 1.111−1.2 = 0.8812
- 0.9938^50 = 0.7327
- eGFR = 142 × 1 × 0.8812 × 0.7327 = 91.7, so 92 mL/min/1.73 m², category G1
For a 50-year-old woman with the same creatinine, κ is 0.7. That gives 142 × 1.429^−1.2 × 0.7327 × 1.012 = 69, category G2.
GFR categories
| Category | eGFR | Description |
|---|---|---|
| G1 | 90 or above | 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 | below 15 | Kidney failure |
These categories come from the international KDIGO guidelines. Chronic kidney disease (CKD) is diagnosed when eGFR stays below 60 for at least three months, or when there are other signs of kidney damage such as albumin (protein) in the urine, even with a normal eGFR. A single result is never enough: doctors repeat the test and check urine before making a diagnosis. GFR also falls gradually with age, so a value in the 60s can be normal for an older adult.
When the estimate is less reliable
Because creatinine comes from muscle, eGFR can be misleading for people with much more or less muscle than average. That includes bodybuilders, people taking creatine supplements, amputees, and people who are frail or have muscle-wasting conditions. It is also less accurate during pregnancy, in acute kidney injury when kidney function is changing quickly, in children (who need a different equation), and after a large meat meal. In these cases doctors may use a cystatin C blood test or a measured GFR instead.
This calculator is for general information and is not a diagnosis. Your doctor will read your eGFR together with your urine tests, blood pressure, medicines and history, so talk to them about what your result means for you.
Frequently asked questions
Why doesn't the equation use race anymore?
In 2021, a joint NKF and American Society of Nephrology task force recommended removing race from kidney function equations. The race term could overestimate kidney function in Black patients and delay care. The 2021 CKD-EPI equation was refitted without it.
My lab report already shows an eGFR. Why is it different?
Some labs still use an older equation, round differently, or use a different creatinine conversion factor. Small differences of a few points are normal. If the gap is large, check that you entered the right unit, and ask your doctor which equation the lab uses.
What is a normal GFR?
For young adults, GFR is usually above 90 mL/min/1.73 m², and it declines slowly with age. Results of 60 or more with no other signs of kidney damage are not considered kidney disease. Your doctor can tell you what is expected for you.
Can I improve my eGFR?
A single high creatinine can come from dehydration, intense exercise or a large meat meal, so a repeat test may be higher. For long-term kidney health, the main steps are controlling blood pressure and blood sugar and avoiding medicines that strain the kidneys. Talk to your doctor before changing any medicine or supplement.
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Results are estimates for general information and are not medical advice. Talk to a doctor or other qualified professional about your health. See our disclaimer.