About the eGFR Calculator
Your kidneys filter your whole blood volume dozens of times a day, and the rate at which they do it — the glomerular filtration rate, or GFR — is the best single measure of how well they are working. Measuring it directly is fiddly, so in everyday practice it is estimated from a blood test for creatinine, together with age and sex. That estimate is the eGFR printed on most routine blood results.
This eGFR calculator uses the 2021 CKD-EPI creatinine equation, the current standard in US laboratories. It accepts creatinine in mg/dL or µmol/L, shows the working, and places the result in the KDIGO category used worldwide.
It also explains two things that often get lost: why the 2021 equation dropped the race coefficient its predecessor used, and why an eGFR figure on its own does not diagnose kidney disease.
How to Use the eGFR Calculator
Choose the units on your blood result. US labs usually report creatinine in mg/dL; labs in the UK, Europe, Canada and Australia usually use µmol/L.
Enter your serum creatinine, your age and your sex. The equation is designed for adults, so ages under 18 are not accepted — children's kidney function is estimated with different equations that use height.
How the eGFR Equation Works
eGFR = 142 × min(Scr/κ, 1)^α × max(Scr/κ, 1)^−1.200 × 0.9938^age × 1.012 [female]
κ = 0.7 (female), 0.9 (male)
α = −0.241 (female), −0.302 (male)The result is in mL/min per 1.73 m² — millilitres filtered per minute, scaled to an average adult body surface area so that results compare fairly between people of different sizes.
The min and max terms give the curve a deliberate bend at a knot, κ. Below the knot, creatinine is weighted by a shallow exponent; above it, by a steep one. At exactly the knot, both terms equal 1, so the two halves join smoothly without a jump.
Step-by-Step Example
Woman, 50, creatinine 1.0 mg/dL.
Scr / κ: 1.0 ÷ 0.7 = 1.429 (above 1, steep exponent)
Creatinine: 1.429^−1.200 = 0.652
Age: 0.9938^50 = 0.733
Sex: × 1.012
eGFR: 142 × 0.652 × 0.733 × 1.012 = about 69A man of the same age with the same creatinine would get about 92. The difference reflects the lower average muscle mass in women: the same creatinine means different kidney function.
Why the Race Coefficient Was Removed
The 2009 CKD-EPI equation multiplied the result by 1.159 for Black patients, on the reasoning that Black people had higher average creatinine for a given kidney function because of higher average muscle mass.
That assumption did not hold up well, and the multiplier had real consequences. Inflating eGFR by about 16% could hold a patient above a threshold for diagnosis, specialist referral or a kidney transplant waiting list. In 2021, a joint task force recommended a refit of the equation without race, and US laboratories have largely adopted it. Some other countries still use older equations, so results from different labs are not always calculated the same way.
What Creatinine Can and Cannot Tell You
Creatinine is a breakdown product of muscle. The kidneys clear it, so it rises as filtration falls — but it also rises and falls with muscle mass.
Very muscular people, including bodybuilders, can read falsely low.
People with little muscle — frail older adults, amputees, people with wasting illness — can read falsely high.
A large meat meal or creatine supplements can raise creatinine for a while.
Some medicines, such as trimethoprim and cimetidine, raise creatinine by blocking its secretion without harming the kidneys.
When accuracy matters, doctors can add cystatin C, a different marker less affected by muscle, and combine the two.
Because of all this, a single eGFR is best read as one point on a trend. A change of a few units between tests is often measurement and biology rather than a real change in the kidneys, and doctors look for a sustained direction over months before drawing conclusions.
eGFR Categories
| Category | eGFR | Description |
|---|---|---|
| G1 | 90 or above | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | under 15 | Kidney failure |
Chronic kidney disease means an eGFR under 60 for at least three months, or signs of kidney damage — most often protein (albumin) in the urine — at any eGFR. So G1 and G2 are only CKD when damage is also present, and a single result under 60 needs confirming.
Understanding Your Result
eGFR is the estimate in mL/min/1.73 m².
KDIGO category places it in the six-stage scale above.
Creatinine shows your value in both units.
Worth knowing explains what the category means in practice, and when a result needs confirming.
When Should You Use This Calculator?
When a blood result shows creatinine but not eGFR, or uses an older equation.
When comparing results from labs reporting in different units.
To understand how age and sex affect the same creatinine value.
Not for children, pregnancy or acute illness, where the equation does not apply well, and not for dosing decisions without a clinician.
Common Mistakes
Reading one low result as kidney disease. CKD needs three months, or signs of damage.
Ignoring muscle mass. It moves creatinine independently of the kidneys.
Comparing results made with different equations. 2009 and 2021 give different numbers.
Testing during a sudden illness. eGFR assumes stable creatinine; it is unreliable during acute kidney injury.
Forgetting the urine test. Protein in the urine matters as much as eGFR.
If your eGFR is low or falling, a doctor will look at the trend, a urine test, blood pressure and your medicines together. Nothing here is medical advice.