GFR Calculator (CKD-EPI 2021)
Estimate your glomerular filtration rate — the standard measure of kidney function — from a blood creatinine result. This tool uses the modern race-free CKD-EPI 2021 equation for adults, accepts creatinine in mg/dL or µmol/L, optionally refines the estimate with cystatin C, and maps the result to the KDIGO G1–G5 categories.
How you compare
What eGFR means
Your kidneys filter blood through millions of tiny units called glomeruli; GFR is the volume filtered per minute, normalized to a standard 1.73 m² body surface. Measuring it directly is impractical, so labs estimate it from creatinine — a muscle waste product the kidneys clear. Because creatinine also depends on muscle mass, age, and sex, the CKD-EPI equation adjusts for those factors. Higher is better: healthy young adults sit around 90–120, and values drift down naturally with age. What matters clinically is the level and the trend and whether urine tests show kidney damage.
How it’s calculated
CKD-EPI 2021 creatinine: eGFR = 142 × min(SCr/κ,1)α × max(SCr/κ,1)−1.200 × 0.9938age × 1.012 (if female), with κ = 0.7 (F) / 0.9 (M) and α = −0.241 (F) / −0.302 (M). With cystatin C, the combined 2021 equation is eGFR = 135 × min(SCr/κ,1)α × max(SCr/κ,1)−0.544 × min(Scys/0.8,1)−0.323 × max(Scys/0.8,1)−0.778 × 0.9961age × 0.963 (if female). µmol/L inputs are divided by 88.42. Stages follow the KDIGO CKD guideline; age-typical means are National Kidney Foundation population values.
This is an educational estimate, not a diagnosis, and it cannot replace your lab report or clinician. It is not valid for children, pregnancy, acute kidney injury, dialysis, amputation, or extreme muscle mass, and a single value cannot establish CKD (that requires ≥3 months plus damage markers). If your eGFR is below 60, is falling, or you have diabetes or high blood pressure, discuss results with your doctor — do not change medications on your own.
KDIGO GFR categories (G1–G5)
Source: KDIGO CKD guideline GFR categories; CKD also requires kidney-damage markers or eGFR <60 for ≥3 months.
Worked example
A 55-year-old woman with serum creatinine of 0.9 mg/dL (≈ 80 µmol/L): eGFR = 75.5 mL/min/1.73 m², category G2 — unremarkable for her age (population mean in the 50s is about 93, and G2 alone is not kidney disease without damage markers). Adding a cystatin C of 1.0 mg/L refines the estimate to 76.9. A 65-year-old man at 1.2 mg/dL lands at 67.1, also G2.
Common mistakes
- Entering µmol/L values with the mg/dL unit selected — an 80× error. Check your lab report’s unit first.
- Panicking over one mildly low result; hydration, creatine supplements, recent heavy exercise, and some drugs all move creatinine.
- Reading G1–G2 as “disease” — without albuminuria or other damage markers, eGFR ≥60 is generally adequate.
- Using an adult equation for anyone under 18.
Where it is used
- Understanding the eGFR line on routine blood-panel results.
- Tracking kidney function over time with diabetes or hypertension.
- Medication dose adjustments (clinicians use eGFR or creatinine clearance).
- Screening conversations before contrast imaging or nephrotoxic drugs.
Frequently asked questions
What is a normal eGFR?
Healthy young adults typically run 90–120 mL/min/1.73 m², and eGFR declines gradually with age — population means are roughly 116 in the 20s, 99 in the 40s, and 85 in the 60s. An eGFR of 60 or higher without signs of kidney damage is generally considered adequate.
Does a low eGFR mean I have chronic kidney disease?
Not from one number. CKD is defined by an eGFR below 60, or markers of kidney damage such as albumin in the urine, persisting for more than 3 months. A single low reading can follow dehydration, medications, or a heavy-protein meal — clinicians repeat the test and check urine albumin before diagnosing anything.
Why doesn’t this calculator ask about race?
It uses the CKD-EPI 2021 refit, which removed the race coefficient from the older 2009 equation after a national task force review. The 2021 race-free equations are now the standard recommended by the National Kidney Foundation and American Society of Nephrology and are what most U.S. labs report.
When does adding cystatin C help?
Creatinine tracks muscle mass, so eGFR can read low in very muscular people and high in people with low muscle mass, amputations, or malnutrition. Cystatin C is largely independent of muscle, and the combined creatinine–cystatin equation (eGFRcr-cys) is more accurate than either marker alone — KDIGO suggests it whenever eGFR accuracy matters for decisions.
How do I convert µmol/L to mg/dL?
Divide micromoles per liter by 88.42. For example, 80 µmol/L equals about 0.90 mg/dL. The calculator’s unit toggle does this conversion for you.
Can I use this for a child?
No — CKD-EPI equations are validated for adults 18 and older. Pediatric eGFR uses height-based equations such as the bedside Schwartz formula (0.413 × height in cm ÷ serum creatinine), which a pediatric clinician should interpret.