PonyatnoHow it's calculated
We use the race-free CKD-EPI 2021 creatinine equation (Inker et al., 2021). Creatinine in µmol/L is first converted to mg/dL by dividing by 88.4.
eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^age × 1.012 (if female), where Scr is serum creatinine in mg/dL; κ = 0.7 and α = −0.241 for women, κ = 0.9 and α = −0.302 for men.
The result is in mL/min per 1.73 m² of body surface area, rounded to a whole number. Categories follow KDIGO 2024: G1 90+, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 below 15.
What to know
What eGFR tells you
Your kidneys filter blood through tiny units called glomeruli, and the filtration rate is the main measure of how well they work. It is rarely measured directly; instead it is estimated from creatinine, a waste product from muscle that the kidneys clear. The poorer the filtration, the higher the creatinine and the lower the eGFR.
Chronic kidney disease is not diagnosed from a single number. It requires eGFR below 60 for more than three months, or signs of kidney damage — most often albumin in the urine. That is why G1 and G2 without such signs are not considered kidney disease.
When the estimate is less accurate
Creatinine depends on muscle mass. In very muscular people (athletes, bodybuilders) eGFR comes out too low; with very low muscle mass, frailty, amputations or a vegetarian diet it may come out too high. Creatine supplements and a large meat meal before the test also raise creatinine.
The equation is not meant for children or pregnancy, and it does not work when kidney function is changing quickly — in acute kidney injury, creatinine lags behind the real filtration. In these cases doctors may use cystatin C or a measured GFR.
Why your lab report may show a different number
Some labs still use older equations such as CKD-EPI 2009 or MDRD. A difference of a few units is expected, not an error. What matters more is how your result changes over time.
This calculator is a reference tool, not a diagnosis. Laboratory ranges differ, and the result depends on your health, medicines and other tests. Discuss it with your doctor.
FAQ
What is a normal eGFR?
90 mL/min/1.73 m² or higher is normal filtration (G1). eGFR slowly declines with age, and values of 60–89 are common in older adults. Without protein in the urine, this is not kidney disease.
Do I need to fast for a creatinine test?
Usually not, but a morning test without a large meat meal beforehand is best. Heavy meat intake, intense exercise and creatine supplements the day before can temporarily raise creatinine and lower eGFR.
What happens if my eGFR is below 60?
The test is usually repeated to rule out a one-off dip, along with a urine albumin test. If the decrease is confirmed for more than three months, your doctor will investigate and monitor your kidneys over time.
Why doesn't the equation use race?
Older equations multiplied the result for Black patients. In 2021 the equation was refitted without that coefficient: race is a social category, not a biological measure, and the adjustment caused misclassification.
Can eGFR go up?
eGFR moves with creatinine: after dehydration or hard exercise it can return to your usual level. What you can do for your kidneys depends on the cause — that is a conversation for your doctor.
Sources
Formulas and cut-offs follow clinical guidelines — see sources below.
- Inker LA et al. New creatinine- and cystatin C-based equations to estimate GFR without race. N Engl J Med. 2021;385:1737–1749.
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117–S314.