GFR Kidney Function Calculator
Estimate your eGFR filtration rate and CKD stage from a creatinine result.
Estimated GFR (CKD-EPI 2021)
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mL/min/1.73 m²
Educational estimate, not a diagnosis. Runs entirely in your browser; nothing is uploaded.
How to use this tool
- Enter your serum creatinine from a recent blood test and pick its unit (mg/dL is common in the US, umol/L elsewhere).
- Enter your age in years and select your sex.
- Click Calculate eGFR to see your estimated filtration rate and the matching chronic kidney disease (CKD) stage.
This GFR kidney function calculator uses the 2021 CKD-EPI creatinine equation, the race-free formula recommended by the National Kidney Foundation and ASN for estimating kidney function in adults.
The CKD-EPI creatinine formula
The result is reported in mL/min per 1.73 square meters of body surface area. If you entered creatinine in umol/L, the tool divides by 88.4 to convert to mg/dL before running the equation. The output is an estimate of the eGFR filtration rate, not a direct measurement of kidney function.
How to read the CKD stages
Kidney function stage is grouped by the estimated GFR value:
- Stage G1 (90 or higher): normal or high filtration.
- Stage G2 (60 to 89): mildly reduced.
- Stage G3a (45 to 59): mild to moderate reduction.
- Stage G3b (30 to 44): moderate to severe reduction.
- Stage G4 (15 to 29): severely reduced.
- Stage G5 (under 15): kidney failure.
A G1 or G2 reading is only considered chronic kidney disease when there is other evidence of kidney damage, such as protein in the urine, lasting three months or more.
A real example
Take a 55-year-old woman with a serum creatinine of 1.0 mg/dL. For females, k = 0.7 and a = -0.241, so Scr/k = 1.0 / 0.7 = 1.4286. Since that is above 1, the min term is 1 and the max term is 1.4286. The math becomes 142 x 1^-0.241 x 1.4286^-1.200 x 0.9938^55 x 1.012, which works out to roughly 60 mL/min/1.73 m². That places her at the boundary of stage G2, mildly reduced kidney function.
Common questions
What is the difference between GFR and eGFR?
GFR is the actual rate your kidneys filter blood, which is hard to measure directly. eGFR is an estimate calculated from a blood creatinine level plus age and sex using an equation like CKD-EPI 2021.
Why does this calculator not ask for race?
The 2021 CKD-EPI creatinine equation was deliberately built without a race coefficient. It is the current race-free standard, so this tool only needs creatinine, age, and sex.
Is a single eGFR reading enough to diagnose kidney disease?
No. Chronic kidney disease is defined by reduced function or kidney damage that lasts at least three months. One result can be affected by hydration, recent meals, or muscle mass, so doctors look at trends and other tests.
Can this tool be used for children?
No. The CKD-EPI equation is validated for adults aged 18 and older. Children use a different formula based on height, so this calculator is not appropriate for them.
My eGFR is below 60, what should I do?
Share the result with a healthcare professional. A value under 60 may simply need a repeat test, but only a clinician can interpret it alongside your full history and other lab work.