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GFR Calculator: eGFR with the CKD-EPI 2021 Equation
Estimate your glomerular filtration rate from age, sex and serum creatinine with the 2021 race-free CKD-EPI equation, and see which GFR category the number falls in. This is an adult estimate for learning, not a diagnosis.
The CKD-EPI 2021 equation
Glomerular filtration rate (GFR) is the volume of blood the kidney filters each minute. Measuring it directly needs a special test, so laboratories report an estimated GFR (eGFR) from blood creatinine, age and sex. The 2021 refit of the CKD-EPI creatinine equation, published by the CKD-EPI group and endorsed by the National Kidney Foundation and the American Society of Nephrology, removed the race coefficient used in the 2009 version:
eGFR = 142 × min(Scr/k, 1)a × max(Scr/k, 1)−1.200 × 0.9938age × 1.012 [if female]
Here Scr is serum creatinine in mg/dL, k is 0.7 for women and 0.9 for men, and a is −0.241 for women and −0.302 for men. The min and max terms mean the formula behaves differently below and above the k threshold. Micromoles per litre are converted by dividing by 88.4.
A worked calculation
Take a man aged 50 with creatinine 1.0 mg/dL. Dividing by k = 0.9 gives 1.111. Because this is above 1, only the max term matters: 1.111 raised to the power −1.2 is about 0.881. The age term is 0.9938 raised to the power 50, which is about 0.733. Multiplying 142 × 0.881 × 0.733 gives roughly 91.7 mL/min/1.73 m², which sits at the border of categories G1 and G2.
The units of the result are millilitres per minute per 1.73 square metres of body surface, a standard adult body size. The calculator therefore does not need your weight or height, which is a strength for routine use and a weakness for people whose body size is far from average.
GFR categories and what they mean
| Category | eGFR | Description |
|---|---|---|
| G1 | 90 or more | Normal or high |
| G2 | 60 to 89 | Mildly decreased |
| G3a | 45 to 59 | Mild to moderate decrease |
| G3b | 30 to 44 | Moderate to severe decrease |
| G4 | 15 to 29 | Severe decrease |
| G5 | under 15 | Kidney failure range |
These bands follow the KDIGO chronic kidney disease guideline. A diagnosis of chronic kidney disease needs abnormal results lasting at least three months, usually with a urine albumin test, so a single number from this page cannot say whether you have it.
When the estimate misleads
Creatinine comes from muscle, so very muscular people may show a low eGFR despite healthy kidneys, while people with low muscle mass, amputations, frailty or a vegetarian diet may look better than they are. Eating a large cooked-meat meal, intense exercise, some drugs and dehydration can shift a single creatinine value. In these situations clinicians may use cystatin C or a measured GFR.
The equation is validated for adults with stable kidney function. It should not be used for children, in pregnancy, during acute kidney injury, in dialysis, or after a transplant without guidance. Drug doses that depend on kidney function may use a different method, so never change a medicine from this estimate. This page is educational and not medical advice.
Worked example
A 60-year-old woman has a serum creatinine of 0.8 mg/dL on a routine blood test.
Inputs
| Sex used in the equation | Female |
|---|---|
| Age | 60 years |
| Serum creatinine | 0.8 |
| Creatinine unit | mg/dL |
Result
GFR category G2: Mildly decreased.
| Creatinine used | 0.80 mg/dL (71 umol/L) |
|---|---|
| Constants for this sex | k = 0.7, exponent = -0.241 |
| Creatinine divided by k | 1.143 |
| Category | G2 (Mildly decreased) |
- Categories G1 and G2 count as chronic kidney disease only when other signs of kidney damage, such as protein in the urine, are present for three months or more.
Medical disclaimer: This tool is for education and general planning. It is not medical advice and does not diagnose any condition. If you are pregnant, under 18, have an eating-disorder history or a medical condition, speak to a doctor or registered dietitian before changing your diet or exercise.
Frequently asked questions
What is a normal GFR?
An eGFR of 90 or above is usually called normal or high, but kidney function slowly declines with age, and the numbers need context from your doctor. Values from 60 to 89 are common in older adults without other signs of kidney damage.
Why was the race coefficient removed from the equation?
The 2021 CKD-EPI refit was developed without a race term after a US task force recommended dropping it, because race is a social construct and not a biological measure of kidney function. The new equation is used by many laboratories.
How do I convert creatinine from umol/L to mg/dL?
Divide the micromole per litre value by 88.4. For example, 88.4 umol/L equals 1.0 mg/dL. The calculator does this automatically when you select the micromole unit.
Can I use this for a child?
No. This equation is for adults. Children usually need a different, bedside Schwartz-type equation interpreted by a paediatric specialist.
Does a low eGFR mean I have kidney disease?
Not necessarily. A single low value can come from dehydration, illness, medicines or muscle mass. Kidney disease is confirmed by repeated results over at least three months along with urine tests and a clinical review.
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References and sources
- Inker LA, et al. (2021). New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. New England Journal of Medicine 385:1737-1749.
- KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease (GFR and albuminuria categories).
- National Kidney Foundation, information on eGFR and kidney disease. Link