A GFR calculator estimates how well your kidneys filter blood, called the estimated glomerular filtration rate (eGFR), from a creatinine blood test, your age and sex. A 45-year-old man with creatinine of 1.0 mg/dL has an eGFR of about 95 mL/min/1.73 m² using the 2021 CKD-EPI equation.
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How to use the GFR calculator
- Enter your serum creatinine in mg/dL.
- Enter your age (adults only).
- Choose sex.
- Read your eGFR and compare it with the stages below.
What eGFR measures
Glomerular filtration rate (GFR) is how much blood the kidneys filter each minute, and it is the best overall measure of kidney function. Measuring it directly is complicated, so labs estimate it (eGFR) from a blood test for creatinine, a waste product made by muscles. The GFR calculator uses the 2021 CKD-EPI creatinine equation, which the National Kidney Foundation recommends for adults. It does not use race.
The 2021 CKD-EPI equation
- eGFR = 142 × min(Scr/κ, 1)α × max(Scr/κ, 1)−1.200 × 0.9938age × 1.012 (if female)
- Scr = serum creatinine in mg/dL
- κ = 0.7 for females, 0.9 for males
- α = −0.241 for females, −0.302 for males
The result is in mL/min/1.73 m², adjusted to an average body surface area.
GFR calculator worked example
For a 45-year-old man with a creatinine of 1.0 mg/dL: Scr/κ = 1.0 ÷ 0.9 = 1.11, so the min term is 1 and the max term is 1.11−1.2 = 0.88. Then 142 × 0.88 × 0.993845 (0.76) ≈ 95. For a 45-year-old woman with the same creatinine, eGFR is about 71, because women typically have less muscle mass and lower creatinine at the same kidney function.
| Creatinine | Age | Sex | eGFR |
|---|---|---|---|
| 0.8 mg/dL | 30 | Female | 102 |
| 1.0 mg/dL | 45 | Male | 95 |
| 1.0 mg/dL | 45 | Female | 71 |
| 1.2 mg/dL | 60 | Male | 69 |
| 1.5 mg/dL | 65 | Male | 51 |
| 2.5 mg/dL | 70 | Female | 20 |
What the numbers mean
Doctors commonly group eGFR into categories (KDIGO stages):
- G1: 90 or higher, normal or high
- G2: 60 to 89, mildly decreased
- G3a: 45 to 59, mildly to moderately decreased
- G3b: 30 to 44, moderately to severely decreased
- G4: 15 to 29, severely decreased
- G5: below 15, kidney failure
An eGFR below 60 for three months or more is a sign of chronic kidney disease. An eGFR of 60 or higher can also be CKD if there are other signs of kidney damage, such as protein in the urine, so an eGFR alone does not rule it in or out. eGFR naturally declines with age.
Limits of creatinine-based eGFR
Because creatinine comes from muscle, eGFR can be misleading for people with very high or very low muscle mass, amputations, extreme diets or recent intense exercise. NIDDK notes that using both creatinine and cystatin C, another blood marker, is more accurate than creatinine alone, and recommends the combined equation when a more precise estimate is needed. The equation is designed for adults with stable kidney function; it is not accurate during sudden kidney injury, in pregnancy or for children, who use different equations.
Creatinine units
The GFR calculator expects creatinine in mg/dL, the unit used in the United States. If your report shows µmol/L, divide by 88.4 before using the GFR calculator: 88 µmol/L is about 1.0 mg/dL.
Talking to your doctor
A single result is a snapshot. Ask your clinician how your eGFR has changed over time, whether a urine albumin test is needed, and how blood pressure, diabetes and medicines affect your kidneys. Use the GFR calculator to understand a lab result, not to diagnose or change treatment.
This tool is for education only and is not medical advice. Kidney function should be assessed by a qualified health professional using laboratory results.
Protecting kidney function
The leading causes of chronic kidney disease in the United States are diabetes and high blood pressure, so keeping blood sugar and blood pressure in their target ranges is one of the most effective ways to protect your kidneys. Other steps include not smoking, staying active, limiting salt and avoiding regular use of NSAID pain relievers unless your clinician approves. If you have diabetes, high blood pressure, heart disease or a family history of kidney failure, ask about yearly blood and urine tests. Recording each result from the GFR calculator alongside your lab dates makes trends easier to discuss at appointments.
Related converters and calculators
Related calculators:
- BMI calculator: body size
- BMR calculator: metabolism
- Protein calculator: protein
- Ideal weight calculator: weight
Sources
National Kidney Foundation: CKD-EPI creatinine equation (2021); NIDDK: Estimating glomerular filtration rate.
Formula and method
eGFR = 142 x min(Scr/k, 1)^a x max(Scr/k, 1)^(-1.200) x 0.9938^age x (1.012 if female). k=0.7 female / 0.9 male; a=-0.241 female / -0.302 male. Scr in mg/dL.
Race-free CKD-EPI creatinine style estimate matching the live expansion formula. Not a lab report or diagnosis.
Questions about this calculator
What is a normal eGFR?
90 or higher is normal or high; values fall with age.
What eGFR means kidney disease?
Below 60 for three months or more, or higher with other kidney damage signs.
Which equation does this use?
The race-free 2021 CKD-EPI creatinine equation.
Can I use µmol/L?
Divide by 88.4 to convert to mg/dL first.
Is it accurate for children?
No, children need pediatric equations.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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