About the GFR Calculator
The glomerular filtration rate, or GFR, is the best overall measure of how well your kidneys filter waste from your blood. Doctors estimate it from a blood test for creatinine, a waste product from muscle, together with your age and sex. This calculator uses the CKD-EPI 2021 equation, the current standard in many countries, which no longer includes a race term. Enter your creatinine in mg/dL or µmol/L, your age and sex, and it shows the estimated GFR in mL/min/1.73 m² and the corresponding stage, G1 to G5. The result is for information only and does not replace your doctor's interpretation.
Updated October 2026
How to use the GFR Calculator
- 1Choose your sex at birth and enter your age.
- 2Choose the unit your lab used for creatinine.
- 3Enter your serum creatinine value.
- 4Read the eGFR and the stage.
- 5Discuss the result with your doctor, who will look at repeated tests.
Worked example
A 50-year-old woman with a creatinine of 1.0 mg/dL has an eGFR of about 68.6, stage G2, which is mildly decreased but not necessarily abnormal for her age. A 40-year-old man with the same creatinine has an eGFR of about 97.6, stage G1. The same creatinine means different filtration for different people, which is why the equation uses age and sex.
If your result is lower than you expected, do not panic. A single low value can come from dehydration, a recent hard workout, a high-protein meal or a lab variation. Doctors usually repeat the test, check your urine for protein and sometimes look at an alternative marker called cystatin C before reaching any conclusion. Bring your list of medicines and supplements to your appointment, because some of them affect creatinine without harming your kidneys.
Converting units
- mg/dL to µmol/L: multiply by 88.4.
- µmol/L to mg/dL: divide by 88.4.
- A creatinine of 1.0 mg/dL is about 88 µmol/L.
- Normal adult creatinine is about 0.6 to 1.3 mg/dL.
- Always use the reference range on your own lab report.
Looking after your kidneys
Control of blood pressure and blood sugar protects the kidneys, as do not smoking, staying active and keeping to a healthy weight. Avoid regular use of anti-inflammatory painkillers if you have reduced function, and drink enough water. Ask your doctor about tests for urine protein, which give extra information beyond GFR.
Related tools
The Blood Pressure Category Checker, the A1C Calculator and the Cholesterol Ratio Calculator help you understand other common health numbers, the BMI Calculator looks at weight for height and the Water Intake Calculator suggests a daily fluid target.
Features
- CKD-EPI 2021 equation
- mg/dL and µmol/L
- Stage G1 to G5
- Adults aged 18 and over
- Checks for unrealistic values
- Private: nothing stored
Frequently asked questions
What is a normal GFR?
A GFR of 90 or higher is considered normal or high for a younger adult, and it declines slowly with age. Many healthy people over 60 have a value of 60 to 89 without kidney disease, so the age and other tests matter.
What do the stages mean?
G1: 90 or more; G2: 60 to 89; G3a: 45 to 59; G3b: 30 to 44; G4: 15 to 29; G5: below 15. Chronic kidney disease is diagnosed when GFR stays below 60 for three months, or when there are other signs of kidney damage such as protein in the urine.
Why use creatinine to estimate GFR?
Creatinine is easy to measure in a blood test and is cleared by the kidneys, so a high level suggests reduced filtering. The equation adjusts for age and sex, which affect creatinine through muscle mass.
Can anything make the result misleading?
Yes. Very high muscle mass, a vegetarian diet, a large meal of cooked meat before the test, some medicines, pregnancy and very low muscle mass can all alter creatinine. Your doctor may use a cystatin C test or a measured GFR instead.
Why was the race term removed?
In 2021 the CKD-EPI equation was refit without a race coefficient, because race is a social, not a biological, category and the old term could delay care for Black patients. Many labs now report the 2021 version.
Is this for children?
No. This equation is for adults. Children use different formulas, such as the bedside Schwartz equation, and should be assessed by a paediatric team.